MEMBRANE TOPOLOGY OF THE MOTA PROTEIN OF ESCHERICHIA-COLI

The MotA protein of Escherichia coli is a component of the flagella th at functions together with the MotB protein in transmembrane proton co nduction. It is an integral membrane protein, with four hydrophobic se gments that might traverse the membrane and two short segments that ar e predicted to be in the periplasm. In a previous study of the accessi bility of MotA to various proteases, evidence for periplasmic segments was not obtained, probably because they are small. Here, we report si te-directed sulfhydryl labeling experiments which show that two segmen ts of MotA are exposed on the periplasmic side of the membrane, while the rest of the protein is in the cytoplasm. These experiments establi sh that the main features of the suggested model for MotA topology are correct, furnishing a basis for more detailed structure-function stud ies of the MotA/MotB proton channel. (C) 1995 Academic Press Limited