Abstract
Bacterial peptidoglycan hydrolases play an essential role in cell wall metabolism during bacterial growth, division, and elongation (autolysins) or in the elimination of closely related species from the same ecological niche (bacteriocins). Most studies concerning the peptidoglycan hydrolases present in Gram-positive bacteria have focused on clinically relevant Staphylococcus aureus or the model organism Bacillus subtilis, while knowledge relating to other species remains limited. Here, we report two new peptidoglycan hydrolases from the M23 family of metallopeptidases derived from the same staphylococcal species, Staphylococcus pettenkoferi. They share modular architecture, significant sequence identity (60%), catalytic and binding residue conservation, and similar modes of activation, but differ in gene distribution, putative biological role, and, strikingly, in their isoelectric points (pIs). One of the peptides has a high pI, similar to that reported for all M23 peptidases evaluated to date, whereas the other displays a low pI, a unique feature among M23 peptidases. Consequently, we named them SpM23_B (Staphylococcus pettenkoferi M23 “Basic”) and SpM23_A (Staphylococcus pettenkoferi M23 “Acidic”). Using genetic and biochemical approaches, we have characterized these two novel lytic enzymes, both in vitro and in their physiological context. Our study presents a detailed characterization of two novel and clearly distinct peptidoglycan hydrolases to understand their role in bacterial physiology.
Highlights
The bacterial cell wall constitutes a very complex environment, within which multiple life processes critical for bacterial survival, such as growth, division, and resistance to antibiotics, are regulated (Kuhn, 2019)
SpM23_A and SpM23_B Are LysostaphinType Peptidoglycan Hydrolases. Both enzymes have a multidomain architecture characteristic of many peptidoglycan hydrolases (Nelson et al, 2012; Vermassen et al, 2019). Their catalytic domains belong to the M23 family of metallopeptidases that are found in lysostaphin, Ale-1, and zoocine A, and they are both linked to a cell wall-binding domain belonging to the SH3b family and present in Lss and Ale-1 (Lu et al, 2006; Becker et al, 2009b)
Despite being identified in the same bacterial host and sharing the same modular architecture and a high degree of amino acid sequence similarity, they display distinct pIs as well as genetic and biochemical features. We concluded that they play different roles in bacterial physiology
Summary
The bacterial cell wall constitutes a very complex environment, within which multiple life processes critical for bacterial survival, such as growth, division, and resistance to antibiotics, are regulated (Kuhn, 2019). Peptidoglycan, which serves as a scaffold for other components of the cell wall, comprises a highly cross-linked heteropolymer consisting of glycan and short peptides (Vollmer et al, 2008a). The precise and tightly controlled cleavage of the peptidoglycan network, which is necessary for the maintenance of its proper function, is delivered by peptidoglycan hydrolases (Vollmer et al, 2008b; Reith and Mayer, 2011; Uehara and Bernhardt, 2011). These comprise a diverse group of enzymes, including muropeptidases, amidases, carboxypeptidases, and endopeptidases. The N-terminal region plays an inhibitory role and has to be processed during enzyme
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