Thesis (Ph.D.) - Cairo University - Faculty of Pharmacy - Department of Microbiology and Immunology

Mycobacteriophages possess different sets of lytic enzymes for disruption of the complex cell envelope of the mycobacteria host cells and release of the viral progeny. Therefore, mycobacteriophage endolysins have emerged as a potential alternative to the current antimycobacterial agents. This study focuses on Lysin B (LysB) enzymes, mycolylarabinogalactan esterases, which cleave the ester bond between the arabinogalactan and mycolic acids in the mycolylarabinogalactan{u2013} peptidoglycan (mAGP) complex in the cell envelope of mycobacteria. A comparative bioinformatics study was performed using multiple in silico techniques e.g. Multiple sequence alignment and structural analysis studies and showed that LysB-D29, the only enzyme with solved three-dimensional structure, shares several common features with esterases (lacking lid domain) and lipases (acting on long chain lipids). Additionally, sequence and structural comparisons of 30 LysB homology models showed great variation in domain organizations and total protein length with major differences in the loop-5 motif harboring the catalytic histidine residue. Docking of different p-nitrophenyl ligands (C4-C18) to LysB-3D models revealed that the differences in length and residues of loop-5 contributed towards wide diversity of active site conformations (long tunnels, deep and superficial funnels, shallow bowls and narrow buried cave) resembling that of lipases, cutinases and esterases. Three LysB enzymes (LysB-D29, -SWU1 and - BabyRay) were recombinantly produced and characterized with respect to their enzymatic and antibacterial activities

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