Probing the Ion Permeability of the Bacterial Translocon with a Locked Translocation Intermediate at the Single Molecule Level

The bacterial translocon SecYEG is responsible for membrane insertion or the translocation of most of membrane and secretory proteins. The idle translocon is sealed to ions by a hydrophobic ring of six isoleucines in its middle and a short helix, the so-called plug (1). Insertion of a polypeptide chain dislocates the plug. By engulfing the chain in a gasket-like manner, the ring is thought to keep the barrier to ions (2). When testing this hypothesis, we found that the complex of SecYEG and a stalled translocation intermediate possesses ion channel activity (3).