Exploring the Enzymatic and Antibacterial Activities of Novel Mycobacteriophage Lysin B Enzymes.

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. Lysin B (LysB) enzymes are mycolylarabinogalactan esterases that cleave the ester bond between the arabinogalactan and mycolic acids in the mycolylarabinogalactan-peptidoglycan (mAGP) complex in the cell envelope of mycobacteria. In the present study, four LysB enzymes were produced recombinantly and characterized with respect to their enzymatic and antibacterial activities. Examination of the kinetic parameters for the hydrolysis of para-nitrophenyl ester substrates, shows LysB-His6 enzymes to be active against a range of substrates (C4-C16), with a catalytic preference towards p-nitrophenyl laurate (C12). With p-nitrophenyl butyrate as substrate, LysB-His6 enzymes showed highest activity at 37 °C. LysB-His6 enzymes also hydrolyzed different Tween substrates with highest activity against Tween 20 and 80. Metal ions like Ca2+ and Mn2+ enhanced the enzymatic activity of LysB-His6 enzymes, while transition metal ions like Zn2+ and Cu2+ inhibited the enzymatic activity. The mycolylarabinogalactan esterase activity of LysB-His6 enzymes against mAGP complex was confirmed by LC-MS. LysB-His6 enzymes showed marginal antibacterial activity when tested alone against Mycobacterium smegmatis, however a synergetic activity was noticed when combined with outer membrane permealizers. These results confirm that LysB enzymes are lipolytic enzymes with potential application as antimycobacterials.

Comparative Structural Analysis of Different Mycobacteriophage-Derived Mycolylarabinogalactan Esterases (Lysin B).

Mycobacteriophage endolysins have emerged as a potential alternative to the current antimycobacterial agents. This study focuses on mycolylarabinogalactan hydrolase (LysB) enzymes of the α/ß-hydrolase family, which disrupt the unique mycolic acid layer of mycobacterium cell wall. Multiple sequence alignment and structural analysis studies showed LysB-D29, the only enzyme with a solved three-dimensional structure, to share several common features with esterases (lacking lid domain) and lipases (acting on long chain lipids). 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 a narrow buried cave) resembling that of lipases, cutinases, and esterases. A set of seven LysB enzymes were recombinantly produced; their activity against p-nitrophenyl esters could be related to their active site conformation and acyl binding site. LysB-D29 (long tunnel) showed the highest activity with long chain p-nitrophenyl palmitate followed by LysB-Omega (shallow bowl) and LysB-Saal (deep funnel).

Immobilization to Positively Charged Cellulose Nanocrystals Enhances the Antibacterial Activity and Stability of Hen Egg White and T4 Lysozyme.

Antibacterial bionanostructures were produced from cellulose nanocrystals (CNC) with immobilized lysozyme from hen egg white (HEW) and T4 bacteriophage, respectively. The nanocrystals were prepared from microcrystalline cellulose by ammonium persulfate oxidation with a yield of 68% and having an average size of 250 nm and low polydispersity index. HEW lysozyme (HEWL) and T4 lysozyme (T4L) were immobilized to CNC by different mechanisms including adsorption and covalent coupling to carbodiimide-activated carboxylate groups and to glutaraldehyde-activated aminated CNC (Am-CNC), respectively. The effect of immobilization on the enzymatic activity (both lytic and hydrolytic) and antibacterial activity of the lysozymes was studied using different methods. Am-CNC-lysozyme conjugates retained the highest lytic activity, 86.3% and 78.3% for HEWL and T4L, respectively. They also showed enhanced bactericidal activity with high potency against Gram-positive as well as Gram-negative bacteria in a relatively shorter time as compared to the free enzymes and resulted in extensive cellular damage, as shown by transmission electron microscopy. The enhanced antibacterial activity was correlated with the increase in zeta potential of Am-CNC-lysozyme conjugates. The immobilized lysozyme preparations further exhibited enhanced storage stability at 4 and 22 °C.