FEATURES OF MOTA PROTON CHANNEL STRUCTURE REVEALED BY TRYPTOPHAN-SCANNING MUTAGENESIS

The MotA protein of Escherichia coli is a component of the flagellar m otors that functions in transmembrane proton conduction. sere, we repo rt several features of MotA structure revealed by use of a mutagenesis -based approach. Single tryptophan residues were introduced at many po sitions within the four hydrophobic segments of MotA, and the effects on function mere measured. Function was disrupted according to a perio dic pattern that implies that the membrane-spanning segments are alpha -helices and that identifies the lipid-facing parts of each helix. The results support a hypothesis for MotA structure and mechanism in whic h mater molecules form most of the proton-conducting pathway. The succ ess of this approach in studying MotA suggests that it could be useful in structure-function studies of other integral membrane proteins.