Remote Coupled Drastic β-Barrel to β-Sheet Transition of the Protein Translocation Motor.

The membrane protein SecDF, belonging to the RND superfamily, enhances protein translocation at the extracytoplasmic side using a proton gradient. Here, we report the crystal structure of SecDF in a form we named Super-membrane-facing (Super F) form, demonstrating a β-barrel architecture instead of the previously reported β-sheet structure. Through this structural insight and supporting results of an in vivo crosslinking experiment, we propose a remote coupling model in which a structural change of the transmembrane region drives a functional, extracytoplasmic conformational transition.