NlpC/P60 domain-containing proteins of Mycobacterium avium subspecies paratuberculosis that differentially bind and hydrolyze peptidoglycan

Abstract

A subset of proteins containing NlpC/P60 domains are bacterial peptidoglycan hydrolases that cleave noncanonical peptide linkages and contribute to cell wall remodeling as well as cell separation during late stages of division. Some of these proteins have been shown to cleave peptidoglycan in Mycobacterium tuberculosis and play a role in Mycobacterium marinum virulence of zebra fish; however, there are still significant knowledge gaps concerning the molecular function of these proteins in Mycobacterium avium subspecies paratuberculosis (MAP). The MAP genome sequence encodes five NlpC/P60 domain-containing proteins. We describe atomic resolution crystal structures of two such MAP proteins, MAP-1272c and MAP-1204. These crystal structures, combined with functional assays to measure peptidoglycan cleavage activity, led to the observation that MAP-1272c does not have a functional catalytic core for peptidoglycan hydrolysis. Furthermore, the structure and sequence of MAP-1272c demonstrate that the catalytic residues normally required for hydrolysis are absent, and the protein does not bind peptidoglycan as efficiently as MAP-1204. While the NlpC/P60 catalytic triad is present in MAP-1204, changing the catalytic cysteine-155 residue to a serine significantly diminished catalytic activity, but did not affect binding to peptidoglycan. Collectively, these findings suggest a broader functional repertoire for NlpC/P60 domain-containing proteins than simply hydrolases.