YhdP forms an envelope-spanning phospholipid-binding bridge in complex with DedD

The outer membrane of Gram-negative bacteria is built from phospholipids synthesised at the inner membrane, but how they cross the periplasm remains unresolved. YhdP is the leading candidate for anterograde phospholipid transfer and is predicted to form an envelope-spanning bridge. Here we purify YhdP at endogenous levels and show by cryo-electron microscopy that it contains a continuous cavity, alongside an additional density that proteomics identifies as the cell wall-binding protein DedD. Liposome co-sedimentation shows that the C-terminal helices of YhdP bind membranes directly, and single-molecule tracking reveals that endogenous YhdP is as immobile as an outer membrane protein, indicating an envelope-spanning architecture in vivo. Native mass spectrometry demonstrates that the YhdP groove accommodates all major classes of E. coli phospholipid without headgroup preference. DedD engages YhdP through its disordered region and increases lipid density at the groove entrance, suggesting a potential role in lipid loading.