A Feedback Control Mechanism Governs the Synthesis of Lipid-Linked Precursors of the Bacterial Cell Wall
Dr. Lindsey Marmont
Thursday, August 10, 2023
10:30 a.m.
PHY-313
Abstract: The bacterial peptidoglycan (PG) cell wall is built from monomeric units linked to a polyprenyl lipid carrier. MraY catalyzes the formation of the first lipid-linked precursor called lipid I by attaching the first sugar of the PG repeat unit to the lipid carrier at the cytoplasmic face of the membrane. Additional enzymes then add the second sugar of the repeat to form the final PG precursor lipid II and flip its disaccharide headgroup across the membrane for polymerization and crosslinking into the mature wall by PG synthases. The polyprenyl carrier undecaprenylphosphate is used to produce many bacterial surface glycans, including the O-antigen (O-Ag) polymers that decorate the outer membrane of gram-negative bacteria. How this limiting lipid carrier is effectively distributed among competing pathways has remained unclear for some time. Here, we describe the isolation and characterization of hyperactive variants of MraY in Pseudomonas aeruginosa. These variants result in the elevated production of lipid II in cells and are hyperactive in a purified system. Amino acid substitutions resulting in this phenotype map to the extracellular side of the MraY dimer interface, which our structural evidence suggests is a binding site for flipped lipid II. Overall, our results are consistent with a model in which MraY is feedback inhibited by lipid II to coordinate precursor supply with PG synthase activity and prevent the sequestration of excess lipid carrier in the PG pathway.