Protein translocation by the SecA ATPase occurs by a power‐stroke mechanism

SecA belongs to the large class of ATPases that use the energy of ATP hydrolysis to perform mechanical work resulting in protein translocation across membranes, protein degradation, and unfolding. SecA translocates polypeptides through the SecY membrane channel during protein secretion in bacteria, but how it achieves directed peptide movement is unclear. Here, we use single‐molecule FRET to derive a model that couples ATP hydrolysis‐dependent conformational changes of SecA with protein translocation. Upon ATP binding, the two‐helix finger of SecA moves toward the SecY channel, pushing a segment of the polypeptide into the channel. The finger retracts during ATP hydrolysis, while the clamp domain of SecA tightens around the polypeptide, preserving progress of translocation. The clamp opens after phosphate release and allows passive sliding of the polypeptide chain through the SecA‐SecY complex until the next ATP binding event. This power‐stroke mechanism may be used by other ATPases that move polypeptides. Synopsis How AAA ATPases harness energy from ATP to promote directional translocation of polypeptides across membranes is poorly understood. Single‐molecule FRET reveals that bacterial SecA uses ATP hydrolysis to push a polypeptide segment into the SecY channel, and phosphate release to slide it through the SecA‐SecY complex. SecA two‐helix finger and clamp domains move upon ATP binding, hydrolysis and phosphate release. ATP binding moves the two‐helix finger towards the SecY channel, causing insertion of the first polypeptide segment into the channel. Upon ATP hydrolysis, finger retraction and clamp domain closure around the translocating polypeptide ensure the translocation progress. Clamp opening induced by phosphate release permits passive sliding of the polypeptide in either direction. Graphical Abstract Single‐molecule FRET reveals that the bacterial SecA translocase uses ATP hydrolysis to push a polypeptide segment into the SecY channel, and phosphate release to slide it through the SecA‐SecY complex.