Electronic Theses and Dissertations (Masters)

Permanent URI for this collection

https://hdl.handle.net/10539/38003

Browse

Browsing Electronic Theses and Dissertations (Masters) by Keyword "Antimicrobial peptides"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Synthesis and characterization of novel short antimicrobial peptides with wound healing properties
    (University of the Witwatersrand, Johannesburg, 2019) Machumele, Khanani Peggy; Makatini, Maya Mellisa
    In recent years, there has been an increasing health crisis due to multidrug-resistant microbes. These pathogens are strains of bacteria that have become resistant to antibiotic drugs. In the year 2016, the World Health Organisation (WHO) had appealed to the members of states in the USA to create a priority list of other bacteria that are resistant to antibiotics in order to support research and development of effective drugs. According to literature, antimicrobial peptides have the potential to be potent agents against pathogens that have multidrug-resistant properties. Despite these studies, there are still substantial limitations (toxicity and susceptibility to proteases) that have affected their clinical and commercial development. In this study, the focus was on bacteria that infect wounds. The lack of potent chronic wound treatment has resulted in an enormous financial and physical burden on patients and the health care system. The stress of multi-resistant microbes heighten the challenges plagued on a patient due to untreatable infected wounds. Peptides which are able to kill bacteria and promote the wound healing process would greatly benefit patients. For example, patients with diabetic foot ulcers are prone to chronic wounds because of their condition, which may lead to amputation. Wound healing antimicrobial peptides are able to kill bacteria in the wound and induce the formation of collagen which will result in fewer amputations. The aim of this proposed research is to develop novel wound healing and antimicrobial compounds by derivatizing bioactive peptides into selective and protease-stable peptidomimetics. Tigerinin RC1 is an antimicrobial peptide with wound healing properties. It was chosen as a starting point for the design of analogues with drug-like properties and it was also conjugated to silver nanoparticle (AgNPs) to improve its bactericidal activity. In this study, 16 Tigerinin RC1 peptide analogues were successfully synthesized using the solid phase peptide synthesis strategy. Peptides were purified using the semi prep-HPLC however, the desired purity of > 90% was only achieved after two or more purification runs. Thus only 4 of the peptide analogues had a purity great than 90% which were KM-PEP-carb, KM-PEP-cyc-amide, KM-PEP-ada and KM-PEP-CT. These peptides were tested for antimicrobial activity and KM-PEP-cyc-amide peptide showed promising results with the minimum inhibitory concentration of 128 μg/ml against P. aeruginosa. Cytotoxicity studies also revealed that conjugation of KM-PEP-carb to AgNPs improved cytotoxicity because when 25 μg/ml of KM-PEP-carb was tested against human T cells the cell viability was -1.48% and when conjugated to AgNPs the cell viability increased to 35.17.
  • Thumbnail Image
    Item
    The Design and Synthesis of Anti-Tubercular Lariatin a Peptidomimetics
    (University of the Witwatersrand, Johannesburg, 2023-07) Nyembe, Priscilla Lebohang; Makatini, Maya Mellisa
    Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is one of the major causes of death and morbidity worldwide. Approximately 10 million people worldwide are infected with Mtb annually, with an estimated 1.5 million deaths. However, potent anti-TB drugs with a new mechanism of action have not been developed in the last thirty years, and only 5 anti-TB drugs are still clinically used. Currently, available drugs and vaccines have failed to control its spread. Furthermore, the emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mtb is a significant public health concern because most of the anti-TB drugs that have been in use for over 40 years are no longer effective for the treatment of these infections. Thus, there is an increased demand for novel anti-tubercular drugs with a different mode of action directed at new Mtb targets. Lariatin A, an anti-mycobacterial peptide, has received interest in the synthesis field due to its distinctive threaded structure which consist of a linear and cyclic portions and its unique bactericidal mechanism toward Mtb. This research focuses on designing and synthesizing derivatives of Lariatin A and investigating their binding properties to the mycobacterium caseinolytic protease (ClpP), a protein essential for the growth of Mtb. A simpler synthetic route for derivatizing Lariatin A peptides was achieved by incorporating two cysteine amino acid residues onto the sequence for cyclization of the peptide via the formation of a disulfide bond instead of a lactam bond. To further simplify the synthetic procedure, derivatives with shorter sequences as well as peptide-peptoids hybrids were also designed. Eight mimetics of Lariatin A were synthesized [Pep_PNL1 (1), Pep_PNL2 (2), Pep_HA (3), Pep_TA (4), Pep_TAA (5), Pep_HAP (6), Pep_PTA (7), Pep_PHA (8)]. The proposed derivatives were synthesized using the solid phase peptide synthesis technique and a sub-monomeric approach was followed to synthesize the peptide-peptoid hybrids. Purification of the peptides was achieved by utilizing semi-preparative High-Pressure Liquid Chromatography and they were characterized by Liquid Chromatography-Mass Spectrometry. The peptides were obtained in low to moderate yields, and the linear tail portion derivative (4) showed 70% ClpP inhibition, while the linear tail derivative coupled to the adamantane moiety (5) showed a 49% inhibition factor. NMR (nuclear magnetic resonance spectroscopy) and CD (circular dichroism) were utilized to determine the secondary structural features. The CD experiments indicated that peptide 1 adopts stable conformations while its separate tail (4) and cyclic (3) regions loss conformity. Pep_PTA (7) displayed the characteristics of both peptide and peptoid as seen from its formation of beta sheets. NMR and CD experiments confirmed that 4 exist in a helical conformation. Hence helical Lariatin A derivatives targeting the Mycobacterium tuberculosis caseinolytic protease can be synthesized using the solid phase peptide synthesis strategy.