Molecular architecture of the PBP2–MreC core bacterial cell wall synthesis complex

Abstract

Bacterial cell wall biosynthesis is an essential process that requires the coordinated activity of peptidoglycan biosynthesis enzymes within multi-protein complexes involved in cell division (the “divisome”) and lateral wall growth (the “elongasome”). MreC is a structural protein that serves as a platform during wall elongation, scaffolding other essential peptidoglycan biosynthesis macromolecules, such as penicillin-binding proteins. Despite the importance of these multi-partite complexes, details of their architecture have remained elusive due to the transitory nature of their interactions. Here, we present the crystal structures of the soluble PBP2:MreC core elongasome complex from Helicobacter pylori, and of uncomplexed PBP2. PBP2 recognizes the two-winged MreC molecule upon opening of its N-terminal region, revealing a hydrophobic zipper that serves as binding platform. The PBP2:MreC interface is essential both for protein recognition in vitro and maintenance of bacterial shape and growth. This work allows visualization as to how peptidoglycan machinery proteins are scaffolded, revealing interaction regions that could be targeted by tailored inhibitors.

An activation pathway governs cell wall polymerization by a bacterial morphogenic machine

“…Biochemical and physiological results indicate that one of these altered PBP2 proteins, PBP2(L61R), not only suppresses MreC defects, it also stimulates Rod system activity in vivo and PG synthesis by RodA-PBP2 fusions in vitro. We infer from the combined set of results that the interaction between PBP2 and MreC is probably not just a scaffolding interaction as proposed previously (Contreras-Martel et al, 2017), but also likely serves a regulatory role in Rod system function by shifting the RodA-PBP2 PG synthase into an activated conformation (Figure 7). Although a direct role for MreC in promoting RodA-PBP2 synthase activity remains to be tested, such an activation mechanism would ensure that the PG synthase is only highly active in the context of the assembled Rod complex thereby providing spatiotemporal control over its function.…”

“…In the structure of the MreC-PBP2 complex, MreC was found to induce a significant conformational change in the membrane-proximal pedestal domain of PBP2, causing two of its subdomains to hinge open ( Figure 2C) (Contreras-Martel et al, 2017). The amino-acid changes in PBP2 that suppress MreC defects mapped to the same region of the protein, suggesting that they may promote a conformation of PBP2 that mimics that induced by MreC.…”

“…In the solved structures of bPBPs (Contreras-Martel, Dahout-Gonzalez, Martins, Kotnik, & Dessen, 2009;Han et al, 2010;Powell, Tomberg, Deacon, Nicholas, & Davies, 2009), this region consists of two interacting subdomains connected by a third subdomain forming a hinge that sits just underneath the catalytic TP domain. In a recently solved structure of an MreC-PBP2 complex from Helicobacter pylori, MreC interacts with the pedestal domain of PBP2 and in doing so causes its two interacting subdomains to swing open (Contreras-Martel et al, 2017) (Figure 2C). The alterations in PBP2 that suppress the MreC defects are not predicted to be at locations directly involved in the PBP2-MreC interface.…”

Essential role for FtsL in activation of septal PG synthesis

“…This allowed us to use FtsL D1-30 to assess the effects of the activation mutations in ftsL and ftsW. Although the ftsW activation mutation had little effect, the addition of two ftsL activation mutations resulted in a strong interaction between FtsL D1- 30 and FtsI and a weaker interaction between FtsL D1- 30 and FtsW (Fig. 7B).…”

FtsW activity and lipid II synthesis are required for recruitment of MurJ to midcell during cell division in Escherichia coli

“…The elongasome is organized by the actin homolog MreB, which localizes underneath the IM in patches in a helixlike distribution. MreB is bound to the membrane by its amphipathic helix, and interacts with the bitopic membrane protein RodZ, the integral membrane proteins MreD and MreC, and the PG synthesis essential proteins RodA  © 2018 John Wiley & Sons Ltd, Molecular Microbiology, 109, 865-884 and PBP2 (Den Blaauwen et al, 2008;van Teeffelen et al, 2011;Morgenstein et al, 2015;Fenton et al, 2016;Contreras-Martel et al, 2017). How the elongasome is regulated is not yet very clear whereas in contrast, cell division has been well investigated.…”