Diversification of LytM Protein Functions in Polar Elongation and Cell Division of Agrobacterium tumefaciens

Abstract

LytM-domain containing proteins are LAS peptidases (lysostaphin-type enzymes, D-Ala-D-Ala metallopeptidases, and sonic hedgehog) and are known to play diverse roles throughout the bacterial cell cycle through direct or indirect hydrolysis of the bacterial cell wall. A subset of the LytM factors are catalytically inactive but regulate the activity of other cell wall hydrolases and are classically described as cell separation factors NlpD and EnvC. Here, we explore the function of four LytM factors in the alphaproteobacterial plant pathogen Agrobacterium tumefaciens. An LmdC ortholog (Atu1832) and a MepM ortholog (Atu4178) are predicted to be catalytically active. While Atu1832 does not have an obvious function in cell growth or division, Atu4178 is essential for polar growth and likely functions as a space-making endopeptidase that cleaves amide bonds in the peptidoglycan cell wall during elongation. The remaining LytM factors are degenerate EnvC and NlpD orthologs. Absence of these proteins results in striking phenotypes indicative of misregulation of cell division and growth pole establishment. The deletion of an amidase, AmiC, closely phenocopies the deletion of envC suggesting that EnvC might regulate AmiC activity. The NlpD ortholog DipM is unprecedently essential for viability and depletion results in the misregulation of early stages of cell division, contrasting with the canonical view of DipM as a cell separation factor. Finally, we make the surprising observation that absence of AmiC relieves the toxicity induced by dipM overexpression. Together, these results suggest EnvC and DipM may function as regulatory hubs with multiple partners to promote proper cell division and establishment of polarity.

Activation of ChvG-ChvI regulon by cell wall stress confers resistance to β-lactam antibiotics and initiates surface spreading inAgrobacterium tumefaciens

“…Considering the possibility that depletion of PBP1a somehow signals for these phenomena, we decided to look at RgsM, another enzyme required for polar elongation. Previous work points to RgsM activity being required for incorporation of nascent PG by PBP1a [17]. However, depletion of RgsM did not cause surface spreading (Fig 1A) indicating that an imbalance of PG hydrolysis and synthesis triggers spreading and the inability pellet in A. tumefaciens .…”

BB0761, a MepM homolog, contributes to Borrelia burgdorferi cell division and mammalian infectivity

“…Originally identified in enzymes that degrade bacterial cell wall, LysM domain is involved in peptidoglycan binding (Buist et al, 2008; Mesnage et al, 2014). LytM domain‐containing proteins have been found in a wide variety of bacteria and have been implicated in an array of important cellular processes such as cell elongation, division, and sporulation (Figueroa‐Cuilan et al, 2021; Peters et al, 2013; Uehara et al, 2009). Searching in SignalP 5.0 (https://services.healthtech.dtu.dk/service.php?SignalP-5.0) further confirmed the putative signal sequence in the N‐terminus of BB0761.…”

“…The M23 peptidases family comprises primarily endopeptidases that degrade bacterial peptidoglycans (Figueroa‐Cuilan et al, 2021; Vermassen et al, 2019). This family is further divided into two subfamilies, M23A and M23B.…”

“…M23B family also contains other non-peptidase homologs such as NlpD, YgeR, and EnvC (Uehara et al, 2010). Consistent with their functions in lysing peptidoglycan, M23 peptidases play important roles in cell wall remodeling, cell morphology, cell growth, cell division, and daughter cell separation (Figueroa-Cuilan et al, 2021;Vermassen et al, 2019). Furthermore, M23 peptidases are also used by some bacteria to lyse other organisms for nutrition or as a defense mechanism (Rawlings et al, 2018).…”

Histidine auxotroph mutant is defective for cell separation and allows the identification of crucial factors for cell division in Brucella abortus

“…In distant organisms such as cyanobacteria, DipM was also found to be involved in cell separation, and is even conserved in chloroplasts of some algae, where it also allows division through PG digestion (Miyagishima et al, 2014). More recently, it has been shown that the homolog of DipM in Agrobacterium tumefaciens (DipM At ) is likely to have broader functions than just the direct hydrolysis of PG to promote cell separation (Figueroa‐Cuilan et al, 2021). Indeed, catalytic residues of the active site of DipM At are not conserved, similarly to their homologs in E. coli , EnvC and NlpD.…”