Earlier reported crystal structure of CLasTcyA revealed unique features like relatively a larger substrate binding pocket, an extended C-terminal loop restricted by a disulfide bond and involvement of residues from hinge region in substrate binding. In present study, CLasTcyA mutants were created to evaluate the importance of these unique features through biophysical characterization. The Val58 in CLasTcyA was replaced by Trp, conserved in most cystine binding proteins, to reduce the size of the binding pocket. All other mutations were created in CLasTcyAV58W mutant as the presence of Trp could be used for intrinsic fluorescence studies. The CLasTcyAV58W showed a noticeable increase in binding affinity and thermal stability as compared to the native form. The mutation of two cysteines in triple mutant CLasTcyAV58W/C212S/C239S, removal of C-terminal extended loop in truncated CLasTcyAV58W/C212S and mutation of His95 from hinge region in the double mutant CLasTcyAV58W/H95A showed a marked decrease in stability-indicating the importance of the unique features in structure of CLasTcyA. The bioinformatics-based virtual screening was employed to screen the potential inhibitor molecules for detailed future studies. The results clearly establish the importance of unique features in structure-function relationship of CLasTcyA.
Keywords: ABC transporters; Candidatus Liberibacter asiaticus; Periplasmic amino acid binding protein; Surface plasmon resonance (SPR).
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