Inhibition of Schistosoma japonicum glutathione transferase by Cibacron Blue: insights from structural, functional and molecular modelling studies

Hlabano, Babongiwe
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Schistosomiasis is a leading neglected tropical disease, caused by blood flukes of the genus Schistosoma. Around 200 million people worldwide are affected, with the majority in Sub-Sahara Africa. Currently, only praziquantel is used for the treatment of schistosomiasis and its exclusive use has led to concerns of rise of praziquantel resistant Schistosomes. There is therefore a need for the development of new anti-schistosomal drugs. Schistosoma species lack the cytochrome P-450 detoxification mechanism, an important mechanism in human detoxification cycle, thus making Schistosoma glutathione S-transferase (GST) one of the main enzyme for detoxification of electrophilic and hydrophobic compounds. Schistosoma japonicum GST (SjGST) is an attractive drug/vaccine target against schistosomiasis. In this study, the mechanism of inhibition of SjGST by Cibacron Blue 3G-A (CB3GA) was investigated. Soluble SjGST was recombinantly expressed and purified successfully to homogeneity. SjGST maintained dimeric structure in the presence of CB3GA. IC50 value of CB3GA was determined to be 100 nM. Michaelis-Manten kinetic studies where performed in the presence and absence of CB3GA and showed that SjGST has high affinity for glutathione compared with CDNB. Lineweaver–Burk plots indicated that CB3GA is an uncompetitive and mixed inhibitor to the G-site and H-site respectively. Induced fit docking predicted that CB3GA binds to the L-site consistent with kinetic inhibition studies. MM-GBSA predicted free binding energy of SjGST and CB3GA was ΔGPred = -310 kJ/mol compared with experimental free energy of binding of ΔGExp = -49 kJ/mol. CB3GA is an efficient inhibitor of SjGST that binds to the dimer interface of SjGST altering catalytic activity of both the G-site and H-site. The unique characteristic of the L-site provides an opportunity for highly specific rational drug design.
A dissertation submitted to the Faculty of Science, University of the Witwatersrand Johannesburg, in fulfilment of the requirements for the degree of Master of Science. July, 2018
Hlabano, Babongiwe (2018) Inhibition of Schistosoma japonicum glutathione transferase by Cibacron Blue : insights from structural, functional and molecular modelling studies, University of the Witwatersrand, Johannesburg, <>