Conformational regulation of two essential activators of bacterial cell elongation

Rod-shaped bacteria rely on the Rod complex to synthesize and maintain their peptidoglycan (PG) cell wall during growth. While the enzymatic machinery at its core is well studied, the role of accessory proteins within the complex remains unclear. In this study, we use cryoelectron microscopy and single-molecule Förster resonance energy transfer (FRET) experiments to demonstrate that two such factors, MreC and MreD, interact through multiple membrane-proximal interfaces. This interaction results in a conformational change in MreC that likely facilitates its interaction with the core synthase components. Disrupting the MreC–MreD interaction in Escherichia coli impairs bacterial growth, highlighting a key regulatory step in cell wall construction and suggesting an alternative avenue for antibiotic development. The peptidoglycan (PG) cell wall is critical for bacterial growth and survival and is a primary antibiotic target. MreD is an essential accessory factor of the Rod complex, which carries out PG synthesis during elongation, yet little is known about how MreD facilitates this process. Here, we present the cryoelectron microscopy structure of Thermus thermophilus MreD in complex with another essential Rod complex component, MreC. The structure reveals that a periplasmic-facing pocket of MreD interacts with multiple membrane-proximal regions of MreC. We use single-molecule FRET to show that MreD controls the conformation of MreC through these contacts, inducing a state primed for Rod complex activation. Using Escherichia coli as a model, we demonstrate that disrupting these interactions abolishes Rod complex activity in vivo. Our findings reveal the role of MreD in bacterial cell shape determination and highlight its potential as an antibiotic target.