Structure of a Proton-Powered Motor that Drives Protein Transport and Gliding Motility

Abstract

Ion-driven motors are amongst the most fascinating protein nanomachines known. The archetypes of the three classes identified to date are ATP synthase, the bacterial flagellar motor, and a proton-driven motor that powers gliding motility and protein secretion in Bacteroidetes bacteria. Here we present the structure of the Bacteroidetes gliding motility motor. The motor is an asymmetric inner membrane protein complex in which the single transmembrane helices of two periplasm-spanning GldM proteins are positioned within a ring of five GldL proteins. Combining mutagenesis and single-molecule tracking, we identify protonatable amino acid residues within the transmembrane domain of the complex that are important for motor function. Our data imply a mechanism in which proton flow leads the periplasm-spanning GldM dimer to rotate with respect to the intra-membrane GldL ring to drive processes at the bacterial outer membrane.