Chaperone that functions as a gatekeeper on the extracellular side of the Sec translocon. Facilitates the translocation of precursor proteins across Sec by interacting with the translocating substrate. Also plays a role in the release of newly synthesized secreted proteins at the extracellular exit site of the Sec translocon. Interacts with the Sec translocon (By similarity). Binds to the lateral gate of SecY (By similarity). Forms a complex with YfgM (By similarity). Located at the lateral gate of SecY. Belongs to the PpiD chaperone family. Could be the product of a pseudogene. Contains an internal deletion relative to its orthologs.