Nagoya University · Biochemistry, Genetics and Molecular Biology
Professor Michio Homma's research lab specializes in bacterial motility, with a primary focus on the structure, assembly, and function of the bacterial flagellum. The lab investigates the molecular mechanisms underlying flagellar rotation, ion-driven motor function, and the dynamic assembly of flagellar components such as the hook, filament, and stator complexes. Using a combination of genetic, biochemical, and imaging techniques—including immunoelectron microscopy and fluorescent protein tagging—the lab elucidates the roles of key proteins like HAPs, PomA/B, MotX/Y, and the T ring in flagellar biogenesis and motility. Their work provides fundamental insights into how bacterial cells achieve directed movement through complex environments.
Figures are computed from collected data and may differ slightly.
Within the bacterial flagellum the basal-body rod, the hook, the hook-associated proteins (HAPs), and the helical filament constitute an axial substructure whose elements share structural features and a common export pathway. We present here the amino acid sequences of the hook protein and the three HAPs of Salmonella typhimurium, as deduced from the DNA sequences of their structural genes (flgE, flgK, flgL and fliD, respectively). We compared these sequences with each other and with those for t
The bacterial flagellar motor is driven by the electrochemical potential of specific ions, H(+) or Na(+). The motor consists of a rotor and stator, and their interaction generates rotation. The stator, which is composed of PomA and PomB in the Na(+) motor of Vibrio alginolyticus, is thought to be a torque generator converting the energy of ion flux into mechanical power. We found that specific mutations in PomB, including D24N, F33C and S248F, which caused motility defects, affected the assembly
The four motor proteins PomA, PomB, MotX and MotY, which are believed to be stator proteins, are essential for motility by the Na(+)-driven flagella of Vibrio alginolyticus. When we purified the flagellar basal bodies, MotX and MotY were detected in the basal body, which is the supramolecular complex comprised of the rotor and the bushing, but PomA and PomB were not. By antibody labelling, MotX and MotY were detected around the LP ring. These results indicate that MotX and MotY associate with th
Of the flagellar filamentless mutants of Salmonella typhimurium, the flaV, flaU, and flaW mutants, which are defective in hook-associated proteins, synthesized flagellin molecules, but flagella did not polymerize at the tips of the mutant hooks and were excreted into the culture medium as intact monomers.
flaFIX, the structural gene for the periplasmic P ring of the flagellar basal body of Salmonella typhimurium, was cloned. Two gene products with apparent molecular weights of 38,000 and 40,000 were identified by minicell analysis. Data from pulse-chase and membrane fractionation experiments and data on the inhibitory effect of the proton ionophore carbonyl cyanide m-chlorophenylhydrazone all indicated that the 40-kilodalton protein was a precursor form which, after export across the cytoplasmic
Hooks of the flagella of Salmonella typhimurium were purified from an flaL mutant. Hook-associated proteins, namely HAP1, HAP2, and HAP3, were separated from them, and the antibody against each HAP was prepared. By immunoelectron microscopic observation, these three kinds of antiHAP antibodies were found to bind on the distal ends of hooks of filamentless mutants consistently with their composition of HAPs. The antiHAP2 antibody bound to the very tops of the claw-shaped ends of the hooks which c
The hooks of the flagella of Salmonella typhimurium were purified by a newly developed method, using a flaL mutant without a filament, and the hook components were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. As a result, we detected three protein species in addition to hook protein. We call these three proteins hook-associated proteins (HAPs). Their molecular weights were 59,000 for HAP1, 53,000 for HAP2, and 31,000 for HAP3. The HAP1/hook protein/HAP3/HAP2 molar ratio
Immunological methods were used to examine the flagellin production of Salmonella typhimurium strains that carried a mutation in one of the two possible genes for flagellin (H1 or H2) and also were incapable of expressing the other gene. Some mutants produced flagellin that was excreted into the culture medium; others accumulated flagellin intracellularly. These two phenotypes were detected in both H1 and H2 mutants. The mutation sites were mapped on the corresponding deletion map (consisting of
Vibrio species are Gram-negative, rod-shaped bacteria that live in aqueous environments. Several species, such as V. harveyi, V. alginotyticus, and V. splendidus, are associated with diseases in fish or shellfish. In addition, a few species, such as V. cholerae and V. parahaemolyticus, are risky for humans due to infections from eating raw shellfish infected with these bacteria or from exposure of wounds to the marine environment. Bacterial flagella are not essential to live in a culture medium.
The flaW, flaU, and flaV genes of Salmonella typhimurium LT2 were cloned into pBR322. These genes were mapped on the cloned DNA fragments by restriction endonuclease analysis and construction of the deletion derivatives. Their gene products were identified, by the minicell method, as proteins whose molecular weights were estimated to be 59,000 for the flaW product, 31,000 for the flaU product, and 48,000 for the flaV product. These values are identical to those of three species of hook-associate
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