The bacteria cell wall is composed mostly of peptidoglycan (PG), a three-dimensional mesh which consists of polymerized chains of repeating disaccharide subunits cross-linked by stem pentapeptides. PG plays a key role in shape maintenance, resistance to osmotic pressure, and cell division, and has been a preferential target for antibiotic development for decades.
Peptidoglycan building blocks are synthesized in 3 different compartments in the cell : cytoplasm, membrane, & periplasm (Laddomada et al., 2019).
Proteins that are involved in PG biosynthesis associate into multi-membered complexes that regulate cell division and elongation, and their inhibition or deregulation can lead to defects in cell shape and often lysis and death.
Penicillin-binding proteins (PBPs) catalyze the two last reactions in PG biosynthesis, and interact with several members of the cell division and elongation complexes during the bacterial cell cycle. One of these partners is MreC, a membrane-associated protein that has been shown to form fibers or patches in certain bacteria and is thought to serve as a scaffold for macromolecules involved in cell wall elongation. We structurally & functionally characterized the PBP2:MreC complex and apo PBP2 from the human pathogen Helicobacter pylori (Contreras-Martel et al., 2017) as well as a fibrous, oligomeric form of MreC from Pseudomonas aeruginosa (Martins et al., 2021).
The structures of PBP2 in unbound form (left) as well as of PBP2:MreC (middle). The N-terminal region of PBP2, comprising the head and anchor regions (blue & red), must undergo a conformational change in order to bind its partner molecule MreC. When on its own, MreC self-associates into elongated fibers that form tubes (right).
MreC subunits associate head-to-head in the tube-like fibers, and we showed that three key interacting regions are essential for oligomerization in vitro and for MreC stability in vivo. (bottom) : In order to trace the electron density map, we crystallized the MreC core and its high-resolution structure was used as a model (Martins et al., 2021).
The similarity of MreC sequences in diverse Proteobacteria suggests that MreC from different pathogenic species can behave in a similar way to that from P. aeruginosa.
Flanders P, Contreras-Martel C, Brown NW, Shirley JD, Martins A, Nauta KN, Dessen A, Carlson EE, Ambrose EA (2022). Combined Structural Analysis and Molecular Dynamics Reveal Penicillin-Binding Protein Inhibition Mode with $\beta$-Lactones. ACS Chem. Biol.
Martins A, Contreras-Martel C, Janet-Maitre M, Miyachiro MM, Estrozi LF, Trindade DM, Malospirito CC, Rodrigues-Costa F, Imbert L, Job V, Schoehn G, Attrée I, Dessen A (2021). Self-association of MreC as a regulatory signal in bacterial cell wall elongation. Nature Commun. 12, 2987.
Contreras-Martel C, Martins A, Ecobichon C, Maragno Trindade D, Mattei PJ, Hicham S, Hardouin P, El Ghachi M, Boneca IG, Dessen A (2017). Molecular architecture of the PBP2:MreC core bacterial cell wall synthesis complex. Nature Commun. 8, 776.
Contreras-Martel C, Amoroso A, Woon E, Zervosen A, Inglis S, Martins A, Verlaine O, Rydzik A, Job V, Luxen A, Joris B, Schofield CJ, and Dessen A (2011). Structure-guided design of cell wall biosynthesis inhibitors that overcome $\beta$-lactam resistance in Staphylococcus aureus (MRSA). ACS Chem. Biol. 6, 943-951.