A role for the two-helix finger of the SecA ATPase in protein translocation

Channel hopping: protein translocation through the SecA–SecY complex Newly synthesized proteins are translocated across the eukaryotic endoplasmic reticulum membrane or the prokaryotic plasma membrane through an evolutionarily conserved protein conducting channel or translocon known as Sec61 in eukaryotes and SecY in prokaryotes. In bacteria, the SecA ATPase is thought to be the motor for translocation through the SecY channel. Two papers by Tom Rapoport and colleagues report the long-awaited structure of the SecA–SecY complex from bacteria. The structure, reveals major conformational changes between both partners and suggests that SecA uses a two-helix finger to push translocating proteins into SecY's cytoplasmic funnel. Crosslinking studies provide further experimental support for this mechanism. In a third paper, Osamu Nureki and colleagues present a crystal structure of SecY bound to an anti-SecY Fab fragment revealing a pre-open state of the channel. Together these three papers provide novel insights into the path taken by a translocating protein. In News and Views, Anastassios Economou takes stock of where this work leaves current knowledge of this 'astonishing cellular nanomachine'.