Understanding the Structure–Function Relationship of Lysozyme Resistance in Staphylococcus aureus by Peptidoglycan O‑Acetylation Using Molecular Docking, Dynamics, and Lysis Assay

Lysozyme is an important component of the host innate defense system. It cleaves the β-1,4 glycosidic bonds between <i>N</i>-acetylmuramic acid and <i>N</i>-acetylglucosamine of bacterial peptidoglycan and induce bacterial lysis. Staphylococcus aureus (S. aureus), an opportunistic commensal pathogen, is highly resistant to lysozyme, because of the O-acetylation of peptidoglycan by <i>O</i>-acetyl transferase (<i>oatA</i>). To understand the structure–function relationship of lysozyme resistance in S. aureus by peptidoglycan O-acetylation, we adapted an integrated approach to (i) understand the effect of lysozyme on the growth of S. aureus parental and the <i>oatA</i> mutant strain, (ii) study the lysozyme induced lysis of exponentially grown and stationary phase of both the S. aureus parental and <i>oatA</i> mutant strain, (iii) investigate the dynamic interaction mechanism between normal (de-O-acetylated) and O-acetylated peptidoglycan substrate in complex with lysozyme using molecular docking and molecular dynamics simulations, and (iv) quantify lysozyme resistance of S. aureus parental and the <i>oatA</i> mutant in different human biological fluids. The results indicated for the first time that the active site cleft of lysozyme binding with O-acetylated peptidoglycan in S. aureus was sterically hindered and the structural stability was higher for the lysozyme in complex with normal peptidoglycan. This could have conferred reduced survival of the S. aureus <i>oatA</i> mutant in different human biological fluids. Consistent with this computational analysis, the experimental data confirmed decrease in the growth, lysozyme induced lysis, and lysozyme resistance, due to peptidoglycan O<i>-</i>acetylation in S. aureus