SecDF

SecDF is a bacterial membrane protein complex that participates in protein secretion through the Sec pathway. It consists of two inner-membrane components, SecD and SecF, which form a heterodimer and associate with the SecYEG translocon and the ancillary protein YajC to constitute a functional holo-translocase in many bacteria.

SecD and SecF are integral membrane proteins with multiple transmembrane segments. The SecD subunit contributes large periplasmic regions, while SecF provides a smaller membrane-spanning scaffold. Together, they interact with SecYEG to form a translocation machinery that operates in concert with the cytosolic ATPase SecA.

The primary role of the SecDF-containing holo-translocase is to enhance and coordinate the movement of preproteins across the inner membrane and their proper insertion into the membrane. SecDF uses the proton motive force across the membrane to stimulate translocation and, in some cases, to assist late-stage translocation, reduce backsliding of polypeptide chains, and support folding of secreted or membrane-embedded proteins. Although SecA-driven ATP hydrolysis provides the energy for initial translocation, SecDF contributes energy coupling and quality control that improves efficiency under various growth conditions.

SecDF is widely distributed among bacteria that utilize the Sec pathway, and its presence can affect secretion efficiency and cell physiology. In organisms lacking SecDF, SecYEG and SecA must support translocation alone, often with reduced capacity under high-secretory demand. SecDF, SecYEG, SecA, and YajC together form a core apparatus for protein export in many Gram-negative and some Gram-positive bacteria.