School of Molecular & Cell Biology (ETDs)

Permanent URI for this community

https://hdl.handle.net/10539/38016

Browse

Now showing 1 - 20 of 33

A Clot to Uncover: FOXP3 and SARS-CoV-2 Nucleocapsid Interactions and Their Effect on DNA Binding
(University of the Witwatersrand, Johannesburg, 2024) Mcinnes, Keiran; Fanucchi, Sylvia
During COVID-19, systemic coagulopathy, which can lead to strokes and embolisms, is often observed in COVID-19 patients and may also contribute to long COVID. This coagulopathy is the result of overactivated platelets in circulation that leads to inappropriate clot formation. FOXP3 is a transcription factor involved in platelet development and loss of FOXP3 function leads to platelets that resemble those seen during COVID-19. Thus, FOXP3 may be dysregulated in COVID-19. The SARS-CoV- 2 nucleocapsid (NC) is a multifunctional protein typically associated with viral genome packaging and virion assembly. However, it is also capable of binding DNA and is potentially able to alter regulation of host protein expression. Here, potential interactions between the DNA-binding forkhead domain (FHD) of FOXP3 and the SARS-CoV-2 NC were investigated. Identification of a novel interaction between FOXP3 and SARS CoV-2 NC may provide new clues as to the pathophysiology of COVID-19. To address this aim, both proteins were overexpressed in T7 E. coli, purified via immobilised metal affinity chromatography, and monitored for potential interactions in the absence and presence of DNA using pull-down assays and fluorescence anisotropy. A direct interaction was identified between the two proteins in the absence of DNA. Additionally, it was found that both proteins are capable of binding to DNA at the same time, but excess NC was found to cause FHD dissociation from the FHD- NC-DNA complex. This result implicates NC in FOXP3 dysfunction which may be associated with the coagulopathy and other symptoms seen during COVID-19. Additionally, NC DNA binding does not appear to be driven by the FOXP3 consensus sequence, indicating that FOXP3 may not be the only transcription factor potentially dysregulated by NC
A Phenotype Prediction Framework for Classifying Colorectal Cancer Patients’ Response to FOLFOX Treatment: An Integrated Approach
(University of the Witwatersrand, Johannesburg, 2024) Mashatola, Lebohang; Kaur, Mandeep
Colorectal cancer (CRC), characterised by its prevalence and heterogeneity, poses a significant challenge in understanding drug resistance, especially in the context of FOLFOX treatment. This study presents an innovative methodology that integrates diverse data analysis approaches to address the challenge of predicting the phenotype of CRC patients resistant or sensitive to FOLFOX. The initial analysis involved dierential and co-expression analyses, identifying pivotal hub genes crucial to drug resistance in CRC, regulating intricate molecular networks. Subsequent enrichment analysis revealed their significant roles in biological functions, particularly influencing DNA repair and nuclear division. To capture inherent topological characteristics within genetic expression data, a novel technique utilising topological data analysis (TDA) was employed. By applying persistence homology to generate persistence images, the Vietoris-Rips complex was constructed using the signed-topological overlap matrix, comprehensively capturing numerous topological features, including high-dimensional Betti-1 and Betti-2. This provided valuable insights into the structural patterns of gene expression between the hub genes. Furthermore, the integration of whole-slide images enhanced understanding of tissue anatomy, which is crucial for predicting cancer stages. Using a MobileNet architecture, a deep learning model classified cancer stages, contributing to a holistic understanding of colorectal tumor microenvironments. For predictive modelling of drug resistance, a multilayer perceptron applied topological summaries generated by TDA. The developed framework, GeTopology, exhibited remarkable performance metrics, achieving an overall 83% accuracy in predicting the FOLFOX response, demonstrating a 3% improvement over a previously published phenotype prediction framework (NSCLC ) that utilised similar data modes. Robust accuracies were consistently observed in independent datasets, classifying both cancer patients and healthy individuals. The results indicated an approximate 10% increase in model prediction accuracy compared to NSCLC, emphasising the potential clinical impact of this integrative approach. In conclusion, this study advances the understanding of drug resistance in CRC by proposing a novel approach that integrates topology with histopathological images, oering transformative insights into predictive modelling and precision medicine
Analysing RNA-sequence data for pancreatic ductal adenocarcinoma tissue samples to identify potential biomarkers
(University of the Witwatersrand, Johannesburg, 2023-09) Jamal, Khadija Sanober; Kaur, Mandeep
Pancreatic ductal adenocarcinoma (PDAC) accounts for approximately 90% of pancreatic cancer and is the fourth leading cause of death with a five-year survival rate of less than 10%. Patients are asymptomatic until detection is observed at a metastatic stage, hence contributing massively towards the high mortality rate. This study was conducted to explore PDAC and its two main subtypes, the classical and basal-like subtype, in an in-depth level via bioinformatic analysis. Bioinformatics is a computational approach to evaluate biological data by analysing omics data including genomic expression and proteomic sequences. A workflow consisting of programmes and web-tools was used to analyse PDAC RNA-sequence data. The sample sets were grouped according to tumour, stage, and subtype. The workflow began with quality control using FastQC and Trimmomatic. Alignment of sequencing files and counts were done through HISAT2 and HTSeq. The main component of this workflow was differential gene expression analysis to identify differentially expressed genes (DEGs), statistically significant genes, per compared conditions. WGCNA was used for co-expression analysis to identify the hub genes involved in regulating the biological network. Lastly, in-silico validation was done by using available web tools to support the findings of this workflow. The identified tumour genes included S100A11, PKM, GPRC5A, LAMC2 and ITGA2, which may represent as universal biomarkers as sample extraction was performed from data generated from individuals belonging to 8 different countries. KRT13 and IL6 were identified in the advanced stage and their role in cancer progression have been explored in this current study. The basal-like subtype had CAV1, DCVLD2 and TGFB2 genes that contribute to treatment resistance. The common dysregulated genes in the basal-like subtype and advanced stage were analysed to evaluate the link between subtype and stage which included WNT3A, TP63, KRT13 and IGF2BP. Coexpression analysis revealed hub genes for tumour (KIF4A, SPAG5, RRM2 and AURKA), basal-like subtype (BUB1, DEPDC1 and KIF14) and classical-subtype (PTPRN and CAMK2B). Through a machine learning model, recall, precision and accuracy scores per sample conditions for the DEGs were all above 94%. These potential biomarkers all have significant roles in promoting cancer progression, aggression and resistance. Hence, these may serve as a less invasive screening method for PDAC as DEGs were classified based on tissue or blood (extracellular vesicle) biomarkers. However, further wet laboratory validation is required for these biomarkers.
Antibacterial activity and susceptibility testing of bacterial isolates from nematodes (Cruznema spp.)
(University of the Witwatersrand, Johannesburg, 2023-09) Mothapo, Maletjema Magdeline; Lephoto, Tiisetso E.
Nematodes are unsegmented worms found in different niches associated with a diverse range of bacteria. Various types of nematodes exist including those that are parasitic to insects, known as entomopathogenic nematodes (EPNs). EPNS of genera Steinernema, Heterorhabditis and Oscheuis are symbiotically associated with Xenorhabdus, Photorhabdus and Serratia, respectively. The symbiotic bacteria of EPNs have been reported to produce a broad spectrum of antimicrobial compounds active against human pathogens. The aim of this study was to isolate and identify nematodes and their associated bacteria from soil samples collected from a vegetative farm in Lesotho and study their antimicrobial activity against four species of pathogenic bacteria (E. coli, S. aureus, E. faecalis and P. aeruginosa). An uncharacterized species of Cruznema was isolated and named Cruznema NTM-2021 (GenBank 18S rDNA accession number: OQ408141). Based on the BLASTN search incorporating the phylogenetic analysis of the 16S rDNA region, three genera of bacteria were identified as Alcaligenes sp., Enterobacter sp. and Elizabethkingia sp. The study revealed that all three bacterial isolates were pathogenic to Tenebrio molitor. Symbiosis tests, using lipid agar method demonstrated the ability of the host nematodes to develop and reproduce in the presence of their associated bacteria. Bacterial supernatants of Alcaligenes sp. and Enterobacter sp. showed some inhibitory activity against Escherichia coli and Enterococcus faecalis, by disk diffusion method. Staphylococcus aureus and Pseudomonas aeruginosa were the most resistant bacteria to supernatants of the three isolates. This study also showed that the Alcaligenes, Enterobacter, and Elizabethkingia species isolated from Cruznema NTM-2021 were resistant to ampicillin, amoxicillin, cefuroxime/sodium, vancomycin and cephalothin but susceptible to gentamicin.
Biochemical and biophysical analysis of a hinge region protease variant in HIV-1 subtype C
(University of the Witwatersrand, Johannesburg, 2023-10) Mokhantso, Tshele; Achilonu, Ikechukwu; Sayed, Yasien
HIV-1 protease plays a crucial role in the maturation of the virus by cleaving gag and gag-pol polyproteins. Understanding the structural and functional consequences of mutations in this enzyme is essential for developing effective anti-HIV drugs, especially in the face of emerging drug-resistant variants. This study focused on the N37T↑V+10•D25A mutant, a novel HIV-1 subtype C protease variant harbouring an insertion (↑V) and a substitution (N→T) at position 37, along with 10 naturally occurring polymorphisms. Mutations occurring distal to the active site have long been thought to contribute to drug resistance, with this in mind the study aimed to assess the impact these mutations have on the structure, stability, dynamics and drug binding of HIV-1 protease. The N37T↑V+10•D25A mutant and wild-type (WT•D25A) HIV-1 protease were overexpressed and purified from inclusion bodies formed in Escherichia coli cells using ion-exchange chromatography. Far-UV CD and SE-HPLC analysis showed that N37T↑V+10•D25A exhibited a predominantly β-sheet secondary structure (218 nm trough) and had a homodimeric size of ~23 kDa, respectively, both similar to WT•D25A. Assessment of the local tertiary structure by intrinsic tryptophan fluorescence indicated that the protease retained its tertiary structure in the presence of mutations, with partial exposure of Trp residues (Trp 6, Trp 6', Trp 42/43, and Trp 42'/43’). Overall, the insertion and substitution mutations did not significantly alter the overall structure of HIV-1 protease. However, the conformational stability of N37T↑V+10•D25A was found to be reduced compared to WT•D25A as determined by urea-induced equilibrium unfolding and thermal unfolding experiments. When denatured using urea and temperature, the mutant exhibited a two-state mechanism of unfolding without stable intermediates during the folding and unfolding process. Thermal unfolding experiment determined the melting temperature of N37T↑V+10•D25A as 58 ± 1.2 °C, which is lower than that of the wild type of 62 ± 0.9 °C. This suggests a potential decrease in dimer stability due to the mutations present in N37T↑V+10•D25A. Isothermal titration calorimetry with acetyl pepstatin as a model inhibitor was employed to examine the impact of mutations on drug binding. The enthalpy (ΔH) for WT•D25A and N37T↑V+10•D25A were 35.94 and 36.02 kJ/mol, respectively. The entropy (ΔS) for WT•D25A and N37T↑V+10•D25A was found to be 256.7 and 261.6 J.mol.K, respectively. These differences in thermodynamic parameters between the WT•D25A and N37T↑V+10•D25A proteases, may indicate altered drug-protease interactions. Induced fit molecular docking predicted the binding strengths of both WT•D25A and N37T↑V+10•D25A with nine protease inhibitors (atazanavir, darunavir, fosamprenavir, indinavir, lopinavir, nelfinavir, ritonavir, saquinavir and tipranavir), revealing that specific background mutations, such as P40S present in N37T↑V+10•D25A, significantly decreased the binding energy of the HIV-1 protease to these inhibitors. Molecular dynamics simulations provided insights into the structural dynamics of N37T↑V+10•D25A, showing reduced stability and increased dynamics, particularly in the flaps and hinges of the protease. An increase in flap tip curling and involvement of the cantilever tips were observed to be related to the flap opening mechanism of HIV-1 protease. Interactions between the HIV-1 protease and inhibitors were examined and the radius of gyration and solvent accessible surface area were calculated to evaluate protein compactness and solvent accessibility of the bound inhibitors, respectively. In general, the N37T↑V+10•D25A mutant exhibited decreased compactness when bound to inhibitors, which correlated with the increased solvent exposure of PIs when bound to N37T↑V+10•D25A. This may contribute to the drug resistance mechanisms of the protease, as inhibitors would have difficulty binding the active site and exhibit weaker binding. During the N37T↑V+10•D25A and PI interactions, there was a decrease in hydrogen interactions, which form the basis for protease inhibitor drug-design and these were replaced by water-bridge interactions, which are weaker and can be easily broken. In conclusion, this study provides a comprehensive characterisation of the N37T↑V+10•D25A mutant of HIV-1 protease, shedding light on its structural alterations, conformational stability, drug binding properties, and dynamic behaviour. These findings contribute to our understanding of drug resistance mechanisms in HIV-1 protease and offer valuable insights for the design of more effective inhibitors to combat HIV-1.
Comparison of Saccharomyces cerevisiae and the novel wild yeast used in beer fermentation and their future in industrial biotechnology
(University of the Witwatersrand, Johannesburg, 2024) Zviuya, Patience; Moodley, Sanchia; Rumbold, Karl
The alcohol industry has grown over centuries due to the increase in alcohol demand by customers. Beer consumers now understand the brewing process and they well understand the role of yeast in fermentation. The alcohol industry now has a lot of customers because of the growth that this sector has made, and this has resulted in an increased demand for new beer styles and high flavor profile beers. Due to this demand, research has been conducted on unconventional wild yeasts that can be employed in making beer, demonstrating the variety of fermentation yeasts that are available and capable of enhancing beer quality and producing a wide range of new beer varieties. The commercial S. cerevisiae yeast and eight wild yeasts (Samson’s Saison, Ragnarok, Dark knight, B. brusc, Neipa, The Proletariat, La Trappist and B. clauss) were used to ferment pale ale in different fermentation vessels. The commercial yeast was the control of this research because this yeast has been used for generations in the brewing industry. The wild yeast strains used were identified using sanger sequencing and seven of these yeasts were S. cerevisiae wild species with similarity index of more than 80% and one was B. bruxellensis strain similarity index more than 95% before and after fermentation. The research outcomes demonstrated that most of the wildyeast performed the same as the commercial yeast in terms of physical and chemical parameters however most of the wild yeast produced more volatiles and esters as compared to the commercial brewing yeast. Commercial S. cerevisiae produced the highest alcohol content 4.5% and the average alcohol content for wild yeast was 3.4% because they are challenging to regulate during fermentation and have low alcohol tolerance unlike the commercial yeast that has been harvested and used for generations. Overall, the utilization of unconventional wild yeast to make beer was identified as a promising alternative to produce beers with exotic flavours and alcohol-free beers. Future work identifying specific yeast that suit different fermentation processes and beer types are recommended.
Computational modeling approaches to validate the druggability of the 26- and 28-kDa Schistosoma glutathione transferase enzymes using bromosulfophthalein as a benchmark ligand
(University of the Witwatersrand, Johannesburg, 2024) Valli, Akeel
PHARMACOPHORE MODELS are 3-D representations of the chemical and spatial features required for interaction with a drug target. These. models offer advantages in early-phase drug design by expediting screening experiments and enabling the sampling of highly specific chemical. space subsets, such as those containing quality drug-like candidates. The glutathione transferase enzyme of Schistosoma spp. (SGST) has been identified as an attractive drug target for the novel treatment of human schistosomiasis. We observed selective inhibition of SGST by bromosulfophthalein. Bromosulfophthalein was found to complex with SGST at a drug binding site in the target dimer interface, providing a suitable benchmark for the design of discriminative SGST pharmacophores. The aim of this research is to construct, deploy and evaluate pharmacophore models of the SGST drug binding site. The objectives are: to characterise the SGST drug binding site, to develop the pharmacophore models and finally to evaluate the drug-resolving ability of the models. We observed significant differences in the drug-binding character of SGST, compared to human glutathione transferase (hGST) counterparts, particularly that SGST supports binding of phenol and sulfonate moieties. Five- and four feature pharmacophores were developed for the respective 26- and 28 kDa SGST variants. Finally, the models demonstrated remarkable ability to retrieve candidates displaying drug-like qualities. In conclusion, we characterised and developed pharmacophore models of the drug binding domains from two major SGST variants. Assessment of drug-resolving power validates the capability of the models to sample drug-like chemicals. Altogether, these accomplishments enable efficient and reliable screening toward novel drug treatment for human schistosomiasis
Control of serine dehydratase activity in rat liver
(University of the Witwatersrand, Johannesburg, 2015-02-24) Abed, Suliman; Manchester, K.L.
Gluconeogenesis from amino acids in the liver is enhanced when the utilisation of glucose is limited under various hormonal and dietary conditions, such as diabetes, starvation or administration of a carbohydrate free diet. Pyruvate is of great importance as a carbon source for gluconeogenesis, since the sequence of gluconeogenic reaction is initiated by carboxylation of pyruvate to oxaloacetate. From this point of view, an important physiological role is suggested for serine dehydratase, which catalyses the degradation of serine to pyruvate and ammonia. The relationship of serine dehydratase levels to gluconeogenic activities, however, is poorly understood, A study of the hormonal and dietary control of serine dehydratase activity was carried out in vivo and in vitro in rat liver. Serine dehydratase was assayed by the colorimetric method of Suda and Nakagawa (1971) and the enzymatic method of Wimhurst and Manchester (1973). Both these methods have been found to be suitable since they are in agreement with each other and also give results which compare favourably with other published values. Activities of serine dehydratase from fresh liver and in slices of liver cultured for various periods have been compared. Also a study of the activity of another soluble enzyme, lactic dehydrogenase, was undertaken and the in vivo and in vitro levels were compared.
Differential expression analysis of PMA and 1,25(OH)2D3-induced monocyte-to-macrophage differentiation in THP-1 cells
(University of the Witwatersrand, Johannesburg, 2023-09) Perumal, Kelda Chloe; Meyer, Vanessa; Gentle, Nikki
The process of monocyte-to-macrophage differentiation is studied in vitro through the use of promonocytic model cell lines, such as the THP-1 cell line, where commonly used differentiation inducing agents include phorbol-12-myristate-13-acetate (PMA) and the active metabolite of vitamin D3, (1,25(OH)2D3; VD3). While both induce differentiation, differences in their mechanisms of action, as well as how the end states of the differentiation process differ, are not well understood. Therefore, this study used computational approaches to compare the effects of PMA and VD3 on the differentiation of monocytes into macrophages, using the promonocytic THP-1 cell line. Through the use of RNA-sequencing, gene expression was quantified in differentiated and undifferentiated THP-1 cells, treated with both PMA and VD3. Differential gene expression analysis was performed to determine genes that were differentially expressed as a result of either treatment relative to the untreated cells. This was followed by over-representation analysis to determine the pathways and processes in which the differentially expressed genes (DEGs) were involved. PMA treatment (3 989 DEGs) resulted in more changes in expression relative to VD3 treatment, where only 384 genes were found to be differentially expressed in response to treatment with VD3. Only TFE3, KIT and TRIB1 were observed to be crucial to the process of differentiation, irrespective of treatment. Apart from this, the treatments were observed to largely involve different biological pathways, resulting in cells that were phenotypically distinct from each other at the transcriptional level. This included changes observed in the expression of genes encoding transcription factors known to be involved in the differentiation process, such as CEBPA, GATA2, IRF8 and PU.1, as well as those encoding surface markers representative of monocytes and macrophages, such as CD14, CD64 and CD11b. The expression patterns observed here indicate that, at least at the concentrations and time points included in this study, PMA and VD3 induce macrophage-like cells that are at different stages of differentiation and are not comparable to either each other or primary macrophages. Furthermore, key differences observed in the expression of genes encoding pathogen recognition receptors and cytokines suggest that which differentiation inducing agent is used may have important implications for these cells’ capacity to recognise pathogens and produce cytokines. The findings of this study therefore emphasise that it is crucial to carefully consider the choice of differentiation-inducing agent when using THP-1 cells as an experimental system for studying monocyte-to-macrophage differentiation.
Differential Gene Expression Analysis of PMA Treated Pro-monocytic Cell Lines
(University of the Witwatersrand, Johannesburg, 2023) Kama, Asavela Olona; Meyer, Vanessa; Gentle, Nikki
HL-60, THP-1, and U937 are model cell lines that can undergo myeloid differentiation in vitro, allowing the study of myeloid cell function in drug metabolism, cytotoxicity, and the aetiology of infections. However, the differentiated end-state of these cells is not well characterised. Moreover, cell line-specific differences in the level of gene expression may confound results obtained from such studies. The aim of this study was thus to compare changes in gene expression between HL-60, THP-1, and U937 cells in response to the differentiation agent, phorbol 12-myristate 13-acetate (PMA), 48 hours after treatment. Gene expression profiles were compared across all three cell lines prior to and post-PMA treatment. Differential gene expression analysis between treated and untreated cells was performed using DESeq2 (v 4.2). Gene over-representation analysis was performed using cluster Profiler (v 4.0). HL-60, THP-1, and U937 cells had similar expression profiles prior to PMA treatment, but different sets of genes were significantly differentially expressed in these cell lines 48 h after treatment with PMA. A total of 475 genes were consistently differentially expressed across all cell lines. These genes were found to be involved in phagosome formation and cell cycle transition. HL-60, THP-1, and U937 cells had 944, 1231, and 624 uniquely differentially expressed genes, respectively. These genes were predominantly involved in energy metabolism and pathogen recognition. Overall, THP-1 cells showed greater potential to detect viruses, while U937 cells showed greater potential to detect bacteria. From this, it can be concluded that while all three cell lines did indeed undergo myeloid differentiation, the macrophage-like cell state produced in each case differed between cell lines.
Effects of acidification on the survival of pathogens in reconstituted infant formula
(University of the Witwatersrand, Johannesburg, 2023-10) Nemakonde, Mufunwa; De Maayer, Pieter
Infants are at a high risk of developing food-borne illnesses due to the consumption of powdered infant formulas (PIFs) contaminated by pathogenic microorganisms. These pathogens may be introduced during PIF production, transportation or during preparation and storage due to poor hygiene practices. Therefore, it is important to improve the microbiological safety of PIFs to reduce illness. Manufacturers have added further measures to ensure continued control of pathogenic microorganisms during the reconstitution and consumption, including the addition of prebiotics and probiotics, as well as acidification of the PIFs, which negatively affect the growth of pathogens. Different organic acids have been biologically or chemically added to commercial PIFs, however, little is known about the efficacy of the different acids in controlling pathogen growth post-reconstitution. The present study aimed to evaluate and compare the effects of two acids, namely citrate and lactate, integrated in commercial PIFs from two manufacturers on pathogen growth within the products. In Chapter 1, we present a review of the current literature pertaining to PIF production and consumption, its microbiological safety and key problem pathogens, as well as measures to control these pathogens (with specific emphasis on PIF acidification). In Chapter 2, the methodology of the present study is discussed. The effects of lactate and citrate incorporated in commercial PIFs against eight key PIF pathogens was evaluated using plate-based assays. Furthermore, the efficacy of PIF acidification at different storage temperatures and over prolonged storage periods was determined. Finally, to validate the effect of acidity on controlling pathogen growth, a spectrophotometric approach was used. Chapter 3 presents and discusses the key findings of the study. PIF acidification was found to negatively affect the growth of pathogens in comparison to the non-acidified infant formula. Acidification and storage at suboptimal temperatures resulted in little to no microbial growth. Lactate acidification of PIFs demonstrated greater inhibitory effects against most pathogens compared to citrate acidification. Further, lactate was found to have a bactericidal effect on the growth of some pathogens. Similarly, Luria Broth acidification resulted in the reduction of microbial growth. This validated that the acids and not other constituents of the infant formula were responsible for the inhibitory effect. Finally, Chapter 4 provides a summary of the key findings as well as recommendations and guidance on future studies which could be undertaken to enhance the effective control of pathogens in powdered infant formulas, thereby ensuring a safe and nutritious food source for infants.
Effects of Mg2+, Ni2+ and Ca2+ on ATP binding kinetics of nicotinate nucleotide adenylyltransferase from Klebsiella pneumoniae and Enterococcus faecium: insights from empirical and computational studies
(University of the Witwatersrand, Johannesburg, 2023-07) Van Deventer, Ruan; Achilonu, Ikechukwu Anthony
NNAT is an attractive target for drug development due to its crucial role in NAD+ synthesis. However, its characterisation in ESKAPE species, such as Klebsiella pneumoniae and Enterococcus faecium, remains limited. This study aimed to elucidate the binding mechanism of ATP, a pivotal substrate, to these NNAT species, focusing on the role of divalent metal ion cofactors. KpNNAT and EfNNAT enzymes were overexpressed and purified, yielding approximately 2 mg/ml for both. Various techniques were employed to investigate their properties, including far-UV CD, extrinsic ANS fluorescence, stopped-flow kinetic analyses, and MD simulations. The results revealed that KpNNAT could bind ATP independently of divalent metal ions, but catalytic activity required the presence of Mg2+. The kinetic analysis showed ka values of 5.99 μM-1 .sec-1 without divalent metal ions and 5.72 μM-1 .sec-1 in the presence of Mg2+. The "pseudo"-specific activity values were 0.005 μmol/min/mg without divalent metal ions and 0.374 μmol/min/mg in the presence of Mg2+. Conversely, recombinant EfNNAT exhibited limited ATP association, and the reasons for this remain unclear. Overall, this study shed light on the structural dynamics and functional kinetics of ATP association in both NNAT species. The findings contribute to our understanding of this druggable target and provide insights into the inactivity of EfNNAT, which warrants further investigation.
Elucidating the Structure-Function Relationships of Enterococcus faecium Nicotinate-Nucleotide Adenylyltransferase through X-Ray Crystallography, Computational Modelling and Binding Studies
(University of the Witwatersrand, Johannesburg, 2024) Jeje, Olamide Adetomi; Pandian, Ramesh; Achilonu, Ikechukwu A.
Nicotinate nucleotide adenylyltransferase (NNAT) is a vital enzyme at the heart of NAD biosynthesis, catalysing a crucial reaction that leads to the formation of pyridine dinucleotides. NAD+ is an essential coenzyme in numerous metabolic processes, DNA repair, and cellular signalling. Given its pivotal role, NNAT has emerged as a compelling drug target, particularly for its potential to disrupt the survival mechanisms of bacterial pathogens. By inhibiting NNAT, it is possible to undermine the metabolic integrity of these pathogens, making NNAT a promising focal point in the fight against bacterial infections and antibiotic resistance. However, understanding the structure-function relationship of Enterococcus faecium NNAT (EfNNAT) has remained elusive. Hence, this study aimed to address this gap bycharacterising EfNNAT and validating its potential as a druggable target. EfNNAT was overexpressed and purified using the Escherichia coli system and IMAC purification technique. Subsequently, biophysical characterisation was performed, followed by the determination of the three-dimensional structure in both apo and liganded forms using X-ray crystallography. High-throughput virtual screening, along with SP and XP docking, was conducted using a library of synthesizable flavonoids. Molecular dynamic simulation and fluorescence studies were employed to establish and validate the binding of identified inhibitors to EfNNAT. Successful expression and purification of EfNNAT yielded approximately 101 mg per 7.8 g of wet E. coli cells, with a purity exceeding 98%. High-resolution crystal structures of EfNNAT in native, adenine-bound, and NMN-bound forms were determined at 1.90 Å, 1.82 Å, and 1.84 Å, respectively. These structures provided insights into EfNNAT's substrate preference and revealed a potential allosteric site at the dimer interface of the NMN-bound structure. Virtual screening identified quercetin 3-O-beta-D-glucose- 7-O-beta-D-gentiobioside as the only potential inhibitor from the flavonoid library used. A 500 ns atomistic molecular dynamics simulation showed the compound interacted through hydrogen bonding and water bridges, albeit unstable within the receptor. ANS and mant-ATP fluorescence spectroscopy confirmed quercetin binding, while thermal shift assay revealed minimal impact of the inhibitor on the protein stability and structure. This study establishes a pipeline from expression and purification to structure solution and potential inhibitor identification for EfNNAT, validating its druggability. The mechanistic insights offer a foundation for advancing drug discovery efforts targeting EfNNAT and other bacterial NNAT enzymes.
Establishing and characterizing organoid cultures from colon tissue of South African individuals
(University of the Witwatersrand, Johannesburg, 2024) Du Plessis, Thea-Leonie; Kaur, Mandeep
Colorectal cancer (CRC) has been poorly studied in South Africa, with limited studies on disease progression and development. Studies that have investigated CRC in South Africa have indicated that there is racial disparity between different racial groups that may be attributed to alternative developmental pathways, differences in genetic compositions or CRC initiators that result in these different clinical presentations. Furthermore, the lack of population-based studies substantiates the need for more intensive CRC research. A particular model used to study cancer in general is the use of two-dimensional (2D) cell cultures, which have provided novel insight into many cancers and their development processes. However, these models lack the complex biology observed in vivo. One such model that is gaining research interest is the use of three-dimensional (3D) organoid cultures. Organoids are derived from stem cells and are able to self-organize and mimic the corresponding organ from which they were derived. Research has indicated that organoids are able to maintain cell-type heterogeneity as well as gene expression levels that resemble the organ of origin. Therefore, this project aimed at standardizing a protocol to establish and characterise colorectal organoid cultures from South African patient-derived tissues. Patient samples were obtained from individual patients with informed consent and were processed to generate organoids. The morphology of the organoids was monitored across several days and across passages. Once the organoids had reached maturity and were at passage 2, characterization was performed using real-time quantitative polymerase chain reaction (RT-qPCR) and immunofluorescence which indicated that the genetic composition and spatial localization of cell types of interest in non-cancerous tissue was recapitulated in the organoids. Based on these observations, it is proposed that organoids could be a promising model to investigate CRC disease development and progression and potentially search for novel therapeutics. This project has established the protocols for growing and characterizing organoids from African samples and provides baseline data, and outlines the complexities and issues involved in growing organoid cultures for the future studies
Evaluating the in vitro anti-metastatic effects of silver(I) phosphine complexes on malignant breast cancer cell lines
(University of the Witwatersrand, Johannesburg, 2023-08) Ferreira, Mizan; Engelbrecht, Zelinda; Cronje, Marianne Jacqueline
Breast cancer is the most diagnosed cancer type among females worldwide. Metastasis, the spread of cancer cells from the primary tumour and establishment of macroscopic secondary tumours, is regarded as the most dangerous characteristic of cancer cells as it is responsible for over 90% of cancer-related deaths. Globally there is a lack of drugs available to specifically target or prevent either the dissemination of cells from the primary tumour or the establishment of distant metastases. The purpose of this study was to ascertain whether a series of silver(I) phosphine complexes, which have previously been shown to display anti-cancer properties in vitro, are also effective as anti-metastatic compounds. The migration, invasion and adhesive abilities of two malignant breast cancer cell lines, MCF-7 and MDA-MB-231, in response to silver(I) phosphine treatment were evaluated. In addition, the colony-forming abilities of cells under both anchorage-dependent and -independent conditions were investigated. Furthermore, the effects of silver(I) phosphine treatment on the expression and activities of key metastatic proteins, matrix metalloproteinases (MMPs), were studied. Of the nine complexes evaluated, all of them showed the ability to reduce one or more metastatic steps namely cell migration, invasion through collagen towards a chemoattractant or adhesion to collagen. In addition, a selected number of complexes reduced the colony-forming abilities of MCF-7 and/or MDA-MB-231 cells in culture plates as well as in soft agar. Moreover, three of these complexes increased the in vitro invasion and colony formation of breast cancer cells. Further investigation into complexes showing anti-metastatic abilities revealed that, apart from one complex on MDA-MB-231 cells, anti-metastatic effects were not achieved through a reduction in MMP levels or activities. The findings presented here show the potential for silver(I) phosphine complexes to reduce the in vitro metastatic abilities of breast cancer cells, warranting further investigations into these complexes for their use as anti-metastatic drugs.
Expression and Methylation of Peroxidasin in Breast Cancer Cell Lines
(University of the Witwatersrand, Johannesburg, 2023-07) Falkov, Jemma Lilian; Mavri-Damelin, Demetra
Peroxidasin (PXDN) is a haem-containing extracellular matrix peroxidase protein which forms hypohalous acids in the presence of hydrogen peroxide (H2O2). The predominant role of PXDN is that of a collagen IV crosslinker within the basement membrane. Increased collagen IV deposition has been linked to tissue invasion and metastasis in breast cancer and PXDN has also been shown to assist in the process of epithelial-mesenchymal transition (EMT) in cancer. Various cancer types display dysregulated levels of PXDN expression including breast cancer and this dysregulation has been associated with poor prognosis. This study aimed to investigate whether DNA methylation of the PXDN promoter may be a mechanism through which changes in PXDN expression observed in breast cancer are regulated. Non-invasive MCF-7 and invasive MDA-MB-231 cells were used as models for luminal A and triple negative breast cancer (TNBC) respectively. The HEK-293 cell line was used as a non-cancerous control cell line. DNA methylation levels of the PXDN promoter and PXDN protein expression was investigated in these cell lines through the methods of methylation sensitive PCR (MS PCR) and immunofluorescence microscopy. Relative levels of PXDN expression were determined through immunofluorescence microscopy. Corrected total cell fluorescence (CTCF) analysis of these images revealed the highest PXDN levels to be found within the invasive MDA-MB-231 cell line, which was double that of the MCF-7 cell line. All cell lines were treated with 10 nM β-Oestradiol, which caused an increase in PXDN expression within the MCF-7 and HEK-293 cell lines and a decrease in expression within the MDA-MB-231 cell line to half its untreated value. PXDN was found to be localised in the ECM in all three cell lines. To elucidate the role of DNA methylation, methylation sensitive PCR (MS PCR) was performed on all three cell lines, with four primer pairs spanning a region of 1305 base pairs (bp) within the PXDN promoter. A region of differential methylation was found between the MDA-MB-231 and HEK-293 cell lines between 524 bp and 53 bp upstream of the transcription start site (TSS). This region was unmethylated within the MDA-MB-231 cell line and methylated within the HEK-293 cell line, which correlates with expression differences between these two cell lines and suggests this region could be of regulatory significance. The four primer pairs designed to amplify the PXDN promoter were unable to amplify this region within the MCF-7 cell line. A heterochromatic DNA conformation or a point mutation increasing CpG content creating a thermodynamically ultra-fastened (TUF) region could be the explanation behind this phenomenon, however further research is required to elucidate the mechanism responsible. In conclusion, PXDN shows higher expression in TNBC cells than in luminal A subtype cells. The oestrogen receptor is involved in regulating PXDN expression, however, different mechanisms seem to be at play between the two cell lines. The contribution of CpG methylation to this change in PXDN expression remains unknown, as does the nature of the interaction between the oestrogen receptors and the gene. Further research is required to clarify the mechanisms involved.
HIV-1 subtype C protease: enzyme kinetics, thermodynamics, and X-ray crystal structure
(University of the Witwatersrand, Johannesburg, 2023-09) Dlamini, Nozinhle Precious; Sayed, Yasien
Human immunodeficiency virus (HIV), a precursor for AIDS is still one of the most devastating pandemics in history. In 2021 alone there were 650 000 deaths associated with the virus and the number of people living with the infection was recorded to be 38.4 million globally. Sub-Saharan Africa suffers the most burden of the virus with approximately 8.3 million people living with virus, HIV-1 subtype C is the main driver of the disease in South Africa and accounts for 46% of global infections. Even with these alarming statistics this subtype is not the main focus point for the majority of HIV-1 research which mainly focuses on subtype B though it only accounts for 12% of infections globally. There is no vaccine or cure against HIV; however, great strides have been made in suppressing the virus. Viral suppression drugs have been developed to target different stages of viral replication such as those targeting the three important enzymes (protease, reverse transcriptase and integrase). In this study the focus will be on HIV-1 subtype C protease. This is a homodimeric aspartyl protease with 99 amino acids in each monomer. It plays a crucial role in the replication cycle of HIV-1 by producing mature infectious virions through cleavage of the Gag and Gag-Pol polyproteins. The subtype C protease differs from subtype B protease in that it has eight naturally occurring polymorphisms which are substitution mutations, some occurring in different regions of the protease with some in the fulcrum (T12S, I15V and L19I), others in the hinge region (M36I and R41K), with H69K and L89M found in the loops and I93L in the α helix. In this study, structural and functional characterisation of HIV-1 subtype C protease was carried out. The secondary structure was characterised using far-UV CD, which is a technique that measures the difference in left and right circularly polarised light. The subtype C protease was estimated to be predominantly β-sheeted, with spectra showing a maximum at 195 nm and a minimum between 215-225 nm. Tertiary structure characterisation of protease was performed using fluorescence spectroscopy. The maximum emission at 347 nm close to that of water (350 nm), demonstrated that the tertiary conformation of the HIV-1 protease was conserved, and that the tryptophan residues within the protease are solvent exposed. SE-HPLC was used to characterise the quaternary structure of the protease and the homodimeric size was determined to be approximately 22 kDa. Steady-state enzyme kinetics to assess the catalytic activity of the subtype C protease was performed using a fluorogenic substrate. The activity of the enzyme was confirmed, with the specific activity of 24.22±1.72 µmol. min-1.mg-1 and the binding of the substrate to the HIV-1 protease was demonstrated by the KM value of 79.546±6.491 µM. This correlates to literature indicating that the substrate was weakly bound and that a high substrate concentration will be required to reach the maximum velocity (Vmax), and Vmax was determined to be 0.036±0.003 µmol. min-1. Enzyme kinetics was coupled with displacement isothermal titration calorimetry for determination of thermodynamics parameters using second generation PIs (atazanavir, darunavir and lopinavir). Thermodynamic studies indicated that the HIV-1 protease has a high affinity for LPV (Kd = 1 nM), compared to ATV (Kd = 18.57nM) and DRV (Kd = 42.26 nM) and binding reactions were all spontaneous with ΔG values(ATV = -43.39 kJ/mol, DRV = -41.39 kJ/mol and LPV = -50.51 kJ/mol). The values also indicated that LPV complexed with HIV-1 is more a stable complex. Also, all the binding reactions were exothermic as indicated by the negative ΔH values of ATV = -45.54 kJ/mol, DRV = -55.62 kJ/mol and LPV = -54.71 kJ/mol. The entropy of all the reactions were determined to be unfavourable with the -T∆S of DRV = 14.23 kJ/mol followed by LPV: 4.2 kJ/mol and ATV: 2.15 kJ/mol. Overall this suggested that all the binding reactions were enthalpically driven. Furthermore, the three-dimensional structure of the HIV-1 subtype C protease was elucidated using X-ray crystallography. The three-dimensional structure the HIV-1 CSA (PDB ID: 8CI7) was solved at a 2.4 Å resolution which is better than the 2.7 Å (PDB ID: 3U71) initially solved in our lab. The high-resolution three-dimensional structure of the protease will provide precise information about the arrangement of atoms within the protease molecule, thus enabling the design and development of protease inhibitors that will be specific for the subtype C protease. This study emphasised the significance of investigating subtype C protease in the context of enzyme kinetics, thermodynamics and detailed X-ray crystallography.
Identification and characterisation of the interaction between FOXP2 and the ligand binding domain of oestrogen receptor α
(University of the Witwatersrand, Johannesburg, 2023-10) Lakhi, Aasiya Yakub; Fanucchi, Sylvia
Forkhead box P2 (FOXP2) regulates the expression of various genes and is associated with language and speech, neural development and outgrowth, and cancer. As transcription factors rarely function in isolation, this study aims to investigate whether FOXP2 directly associates with oestrogen receptor α (ER1), a nuclear receptor responsible for sexual differentiation and cancer progression and outcome. The association between ER1 and FOXP2 was first identified in MCF-7 cells using co-immunoprecipitation. Thereafter, the interaction was characterised biophysically by overexpressing the FOXP2’s DNA-binding forkhead domain (FHD) and N-terminal region (NT), and ER1’s ligand-binding domain (LBD) in E. coli cells. Isothermal titration calorimetry and fluorescence anisotropy were used to investigate the thermodynamic parameters and regulation of interaction between FOXP2 FHD and ER1 LBD, respectively. Electrophoretic mobility shift assay was used to investigate the effect of the interaction on FOXP2’s DNA binding ability. Following the successful overexpression and purification of all three proteins, ER1 LBD was found to interact with FOXP2 FHD but not with FOXP2 NT. The affinity of the ER1 LBD for FOXP2 FHD increases with an increase in salt concentration. ITC shows a similar trend and reveals that the interaction is enthalpically favoured at lower salt concentrations but enthalpically opposed at higher salt concentrations. Additionally, the FOXP2-ER1 LBD interaction remains unaffected by the inclusion of oestrogen, but addition of FOXP2 cognate DNA results in inhibition of the formation of the complex. This research identifies a novel interaction between ER1 LBD and FOXP2 FHD and shows that the DNA simultaneously suggesting a probable role of this interaction in regulating the transcriptional pathway of FOXP2. This study serves as a foundation for further investigation into the interaction between FOXP2 and ER1 in different cell lines and its relevance in FOXP2-mediated outcomes in cancer and neurodevelopmental disorders.
Insights into silver(I) phosphine complexes in targeting cell death and metastatic mechanisms in malignant cell lines
(University of the Witwatersrand, Johannesburg, 2023-09) Roberts, Kim Elli; Engelbrecht, Zelinda; Cronjé, Marianne J.
Cancer is the leading cause of death worldwide, with 18.1 million new cases and 9.6 million deaths reported annually. Cisplatin, a popular chemotherapeutic drug, exhibits certain limitations in terms of selectivity and efficacy. This emphasizes the necessity for novel therapeutic approaches in addressing a variety of cancer types. Multiple studies have shown that silver-based compounds suppress cancer cell proliferation and induce apoptosis. Thirteen novel silver(I) mono-dentate phosphine complexes were investigated for their anticancer effects on seven different human malignant cell lines; A375 non-pigmented melanoma, A549 lung adenocarcinoma, HEP-G2 hepatocellular carcinoma, HT-29 colorectal adenocarcinoma, MCF-7 and MDA-MB-231 breast adenocarcinoma, and SNO oesophageal squamous cell carcinoma. Two non-malignant human cell lines, HEK-293 embryonic kidney cells and MRHF foreskin fibroblast cells, were used to assess the selectivity of the complexes. Cisplatin and the efficient silver(I) phosphine complexes were selected for dose-response experiments to determine IC50 concentrations for the respective cell lines. On the basis of these screening results (chapter two), five difficult-to-treat cancer cell lines, and their most efficient complexes were selected for further investigation. Various cellular characteristics were investigated in chapter three (A549, HEP-G2, HT-29); these included morphological changes, ATP levels, GAPDH levels, Ptd-L-Ser externalization, mitochondrial membrane potential, oxidative stress levels, and the activity of a metabolic enzyme, cytochrome P450 isoform CYP1B1. The antimetastatic activity of the selected complexes was assessed by evaluating their ability to impede the migration of A549 cells. The fourth chapter examines the anticancer effect of selected complexes on hormone-dependent (MCF-7) versus triple-negative (MDA-MB-231) breast cells. Changes in morphology, Ptd-L-Ser externalization, alterations in mitochondrial membrane potential, oxidative stress levels, cytochrome c release, and DNA damage were studied. Furthermore, in chapter five, molecular docking simulations were used to determine whether the most potent silver(I) phosphine complex across all cell lines bonds to estrogen receptor alpha (ER-α) and estrogen receptor beta (ER-β). Seven of the thirteen silver(I) phosphine complexes significantly reduced cell viability in malignant cell lines while being less toxic to non-malignant cells. Complex 4 best targeted all cancer types, with IC50 values ranging from 5.75 to 10.80 µM across malignant cell lines. In the malignant treated cells, morphological changes, reactive oxygen species production, mitochondrial membrane depolarization, and Ptd-L-Ser externalization were observed. Complexes 1 and 4 repressed cell migration in the A549 cells. The presence of damaged nuclei, metabolically inactive mitochondria and cytochrome c translocation from the mitochondria’ intermembrane to the cytosol in MCF-7 cells were observed. These findings suggest that complexes 2, 4 and 7 induced apoptotic cell death. Furthermore, in silico computational predictions suggested a promising interaction between complex 4, and ER-α and ER-β. Overall, this study demonstrates the potential of silver(I) phosphine complexes as anticancer agents, with promising effects on various cancer cell lines.
Insights into the Physiochemical Properties of the Interaction between the L38↑N↑L+4 HIV-1 Hinge Mutant Subtype C Protease and a Related Gag Cleavage Site
(University of the Witwatersrand, Johannesburg, 2023-09) Adams, Taryn Racheal; Sayed, Yasien
Frequent mutations in HIV protein drug targets such as the protease (PR), have led to a rise in resistance to clinically available treatments and inquiries into the associated biochemical mechanisms. In this study, the L38↑N↑L+4 PR (mutant) and related gag, were isolated from a PR inhibitor naïve child for further study. Wild-type and mutant PRs were successfully overexpressed and purified using ion exchange chromatography. Intrinsic fluorescence studies probing tryptophan residues located at the hinge revealed variations in tertiary structure. This coincided with significant differences in refolding efficiency (mutant PR recovery ~ 10% and wild-type PR recovery ~ 34%). Furthermore, differences in catalytic efficiency (mutant-specific activity ~ 7.4 µmol.min-1.mg-1, mutant kcat ~ 2.71 sec-1; wild-type specific activity ~ 31.6 µmol.min-1.mg-1, kcat ~ 11.60 sec-1). Thermal shift assays revealed reduced mutant PR structural stability (Tm ~ 67 ℃) compared to the wild-type PR (Tm ~ 64 ℃). Furthermore, reduced stability of inhibitor-mutant PR complexes (Tm ~ 73.5 ℃ Acetyl pepstatin (AP), 90 ℃ Darunavir (DRV), and 88 ℃ Saquinavir (SQV)) compared to complexes involving the wild-type PR (Tm ~ 70 ℃ (AP), 82 ℃ (DRV), and 82 ℃ (SQV)). Overall, the L38↑N↑L+4 PR mutations were found to influence the tertiary structure of the hinge, gag processing, and PI stability within the mutant PR active site. Computational docking studies highlighted the potential role of a gag single nucleotide polymorphism (SNP), located at the 4th amino acid (P4) position of the peptide-2-nucleocapsid (p2/NC) gag cleavage site, for future studies as a compensatory mutation aiding PR polymorphisms. Further studies should focus on the gag-PR functional pair to build a more accurate understanding of HIV drug resistance mechanisms.

Browse

Browsing School of Molecular & Cell Biology (ETDs) by Faculty "Faculty of Science"

Results Per Page

Sort Options