The cell wall hydrolase Pmp23 is important for assembly and stability of the division ring in Streptococcus pneumoniae

Maxime Jacq,Anne Marie Di Guilmi,Katharina Peters,Thierry Doan,Chryslène Mercy,Thierry Vernet,Laure Bellard,Benoit Gallet,Waldemar Vollmer,Christopher Arthaud,Jennifer Galindo,Christophe Grangeasse,Yves V Brun,Michael S Vannieuwenhze,Cecile Morlot,Sylvie Manuse

doi:10.1038/s41598-018-25882-y

Abstract

Bacterial division is intimately linked to synthesis and remodeling of the peptidoglycan, a cage-like polymer that surrounds the bacterial cell, providing shape and mechanical resistance. The bacterial division machinery, which is scaffolded by the cytoskeleton protein FtsZ, includes proteins with enzymatic, structural or regulatory functions. These proteins establish a complex network of transient functional and/or physical interactions which preserve cell shape and cell integrity. Cell wall hydrolases required for peptidoglycan remodeling are major contributors to this mechanism. Consistent with this, their deletion or depletion often results in morphological and/or division defects. However, the exact function of most of them remains elusive. In this work, we show that the putative lysozyme activity of the cell wall hydrolase Pmp23 is important for proper morphology and cell division in the opportunistic human pathogen Streptococcus pneumoniae. Our data indicate that active Pmp23 is required for proper localization of the Z-ring and the FtsZ-positioning protein MapZ. In addition, Pmp23 localizes to the division site and interacts directly with the essential peptidoglycan synthase PBP2x. Altogether, our data reveal a new regulatory function for peptidoglycan hydrolases.

Highlights

During the bacterial division cycle, cell wall synthesis and remodeling are coordinated with membrane constriction, led by the tubulin homologue FtsZ
Among the cell wall hydrolases (CWHs) involved in pneumococcal growth and division, the N-acetylmuramoyl-L-alanine amidase/ endopeptidase PcsB is required for septum splitting[17,21], the putative lytic transglycosylase MltG is required for peripheral cell wall synthesis[20], the D,D-carboxypeptidase PBP3 (DacA) and the L,D-carboxypeptidase DacB limit the amount of crosslinking by trimming the pentapeptide substrates of the penicillin-binding proteins (PBPs) synthases[16,19,22,23,24], and the endo-β-N-acetylglucosaminidase LytB is responsible for the physical and final separation of daughter cells[25]
The enzymatic activity of G-type lysozymes and lytic transglycosylases (LTs) all require a Glu residue that is conserved in Pmp[23] (E61) but near this catalytic position, G-type lysozymes carry an Asn and a second negatively charged catalytic residue that are not conserved in LTs28,29 and are present in Pmp[23] (N119 and E74), suggesting that Pmp[23] might be a G-type lysozyme (Fig. S1)

Summary

Introduction

During the bacterial division cycle, cell wall synthesis and remodeling are coordinated with membrane constriction, led by the tubulin homologue FtsZ This coordination relies on a complex network of transient functional and physical interactions, yet to be fully identified and characterized, between SEDS proteins, PBPs, CWHs, FtsZ and other proteins of the divisome with structural or regulatory functions. Other pneumococcal proteins with a key regulatory function in cell division are CWHs since impairment of their activity or localization leads to severe shape and division defects[15,16,17,18,19,20] Their precise regulatory function in these processes remains unclear. Using 3D homology modeling, genetics, fluorescence microscopy and protein-protein interaction experiments, we provide data supporting the idea that Pmp[23] is a bacterial lysozyme involved in the stability of the division machinery, revealing a new connection between cell wall metabolism and cell division

Methods

Results

Conclusion