The MotA protein of E. coli is a proton-conducting component of the flagellar motor

• Published in: Cell Vol. 60; no. 3; pp. 439 - 449
• Main Authors: Blair, David F., Berg, Howard C.
• Format: Journal Article
• Language: English
• Published: Cambridge, MA Elsevier Inc 09.02.1990; Cell Press
• Subjects: Alleles; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biological and medical sciences; Cell Membrane - physiology; Cell Movement; Escherichia coli; Escherichia coli - genetics; Escherichia coli - growth & development; Escherichia coli - physiology; flagella; Flagella - physiology; Fundamental and applied biological sciences. Psychology; Gene expression; Genes, Bacterial; Genes, Dominant; Genotype; Hydroxylamine; Hydroxylamines - pharmacology; Molecular and cellular biology; Molecular genetics; Mutation; Phenotype; Plasmids - drug effects; Protons; Performance evaluation; Motility; Mutagenesis; Cell permeability; Growth rate; Escherichia coli; Microorganism culture; Bacteria; Gene expression; Escherichieae; Enterobacteriaceae; Proton transport
• ISSN: 0092-8674; 1097-4172
• DOI: 10.1016/0092-8674(90)90595-6

A number of mutants of motA, a gene necessary for flagellar rotation in E. coli, were isolated and characterized. Many mutations were dominant, owing to competition between functional and nonfunctional MotA for a limited number of sites on the flagellar motor. A new class of mutant was discovered in which flagellar torque is normal at low speeds but reduced at high speeds. Hydrogen isotope effects on these mutants indicate that MotA catalyzes proton transfer. We confirmed an earlier observation that overproduction of MotA leads to accumulation of the protein in the cytoplasmic membrane and to significant decreases in growth rate. When nonfunctional mutant variants of MotA were overproduced instead, they accumulated in the cytoplasmic membrane, but growth was not impaired. These results also suggest that MotA conducts protons. This was confirmed by measuring the proton permeabilities of vesicles containing wild-type or mutant MotA proteins.