Facing antibiotic resistance

The cell wall of most Gram-negative and Gram-positive bacteria is composed of peptidoglycan (PG), a mesh-like structure of repeating glycan chains cross-linked by small peptides. Peptidoglycan is essential for growth, division and viability of the microorganism. Any disruption of its biosynthesis results in bacterial cell lysis or cessation of growth, making it a major target for antibiotics. It was suggested that many proteins involved in PG synthesis, from the cytoplasmic enzymes that synthesize the precursor Lipid II to the extracellular enzymes that are responsible for its polymerization, function in vivo as part of a multi- protein complex “machinery”. In particular, recent evidence suggests that the core of the PG biosynthetic complex consists of the class B penicillin binding proteins (PBPs) such as PBP2 and PBP3 that work together with membrane inserted shape, elongation, division and sporulation (SEDs) proteins, FtsW and RodA, respectively. These synthetic machines provide for cell division (FtsW-PBP3) and cell elongation (RodA-PBP2) and are also the key targets of most clinically used ß-lactam compounds. Though structures of both RodA (a SEDS protein involved in bacterial growth and elongation) and type b PBPs are available, the interaction between these proteins and their joint enzymatic activity is poorly characterized. Here, the preliminary structural characterization of a RodA-PBP2 protein complex by single-particle cryogenic electron microscopy (cryo-EM) is presented, aiming at a better understanding of these incredibly important enzymes that could enlighten the future of antibiotics research and development.