Structures of the lipid II flippase from the monoderm pathogen Staphylococcus aureus.

Peptidoglycan biogenesis requires membrane flippases to translocate lipid-linked precursors across the cytoplasmic membrane for processing. This essential step is mediated by MurJ, the lipid II flippase conserved across all peptidoglycan-producing bacteria. While MurJ from diderm bacteria has been structurally resolved in multiple conformational states, its monoderm homolog remains uncharacterized. Monoderm MurJ homologs exhibit substantial sequence divergence yet retain the same lipid II flipping function and are promising antibiotic targets. Here we report structures of Staphylococcus aureus MurJ (SaMurJ) captured in both outward- and inward-facing conformations. These structures show that SaMurJ adopts the conserved MOP family fold and undergoes conformational transitions consistent with an alternating-access mechanism. Our findings reveal conserved and divergent features of MurJ between diderm and monoderm bacteria that are critical for lipid II flipping and provide a structural framework for probing substrate recognition and specific inhibition.