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Location: Infectious Bacterial Diseases Research

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

item Bannantine, John
item Lingle, Cari - University Of Missouri
item Adam, Philip - Oklahoma State University
item Ramyar, Kasra - University Of Missouri
item Mcwhorter, William - University Of Missouri
item Stabel, Judith
item Picking, William - Oklahoma State University
item Geisbrecht, Brian - Kansas State University

Submitted to: Protein Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2016
Publication Date: 1/22/2016
Citation: Bannantine, J.P., Lingle, C.K., Adam, P.R., Ramyar, K.X., McWhorter, W.J., Stabel, J.R., Picking, W.D., Geisbrecht, B.V. 2016. NlpC/P60 domain-containing proteins of Mycobacterium avium subspecies paratuberculosis that differentially bind and hydrolyze peptidoglycan. Protein Science. 25:840-851. doi: 10.1002/pro.2884.

Interpretive Summary: Johne’s disease in livestock such as dairy cattle and sheep is caused by the bacterium Mycobacterium avium subspecies paratuberculosis (MAP). Over 50% of the proteins encoded by the bacterium’s genome are unknown. Therefore, this research takes a step back and describes some fundamental aspects of two proteins we have been studying for years. These proteins are being studied primarily because they are strong antigens and thus could be used to develop a diagnostic test for Johne’s disease. However, in this study we focused on the function of these proteins. Through crystal structure determination and modification of a single amino acid in the proteins, we could determine that both proteins have a similar structure, but one of the proteins lacked enzyme activity. We developed a novel assay to demonstrate this lack of activity and propose reasons why this may occur. This work is of primary interest to other researchers working in the field.

Technical Abstract: While intense research is being conducted to develop faster and more reliable methods for diagnosis of Johne’s disease, there are still significant knowledge gaps concerning the molecular function of Mycobacterium avium subspecies paratuberculosis proteins. Therefore, we describe atomic resolution crystal structures of two proteins, MAP1272c and MAP1204, which are part of the NlpC/P60 superfamily. A subset of proteins containing NlpC/P60 domains are bacterial peptidoglycan hydrolases that cleave non-canonical peptide linkages and contribute to cell wall remodeling as well as separation in cell division. These crystal structures, combined with a functional assay to indirectly measure peptidoglycan cleavage activity, led to the observation that MAP1272c does not have a functional catalytic core for cell wall hydrolysis. Furthermore, the structure and sequence of MAP1272c suggest that the catalytic residues normally required for hydrolysis are absent, perhaps suggesting a role as a binding protein or receptor for the peptide moiety of peptidoglycan. While the NlpC/P60 catalytic triad is present in MAP1204, changing the catalytic cysteine-155 residue to a serine significantly diminished catalytic activity. This is the first example of a catalytically inactive triad for an NlpC/P60 protein in M. avium subspecies paratuberculosis and only the second example in mycobacteria. In sum, these findings suggest a broader functional repertoire for NlpC/P60 domain-containing proteins than simply hydrolases.