Study of the structure and function of pathogenic bacterial virulence factors

The Project Leader's Profile

Yasuhiko Horiguchi

Professor, Dept. of Molecular Bacteriology, Research Institute for Microbial Diseases, Osaka University

In 1982, graduated from School of Agriculture, Osaka Prefecture University. and obtained VMD. In 1987, completed the doctoral course at the graduate school of Agriculture, Osaka Prefecture University and obtained Ph.D. After working in Research Center for Veterinary Science of The Kitasato Institute, was appointed an assistant professor at Research Institute for Microbial Diseases, Osaka University in 1992. In 1998, appointed as an Associate Professor. From 2001, he holds the current position. In 1996, received Kuroya-awards of Japanese Society for Bacteriology. Specialized in bacteriology, cellular biology, and molecular biology and biochemistry of bacterial protein toxin.

Project Leader
  • Yasuhiko Horiguchi, V.M.D., Ph.D., Professor , Dept. of Molecular Bacteriology
Research Members
  • Shigeki Kamitani, Ph.D., Assistant Professor, Dept. of Molecular Bacteriology
  • Hiroyuki Abe, Ph.D., Assistant Professor, Dept. of Molecular Bacteriology
  • Aya Fukui, Ph.D., Assistant Professor, Dept. of Molecular Bacteriology
  • Hirono Toshima, M.S., Research Fellow, Dept. of Molecular Bacteriology


Pathogenic bacteria establish infectious diseases by modifying the function of host cells. In other words, various lesions and symptoms of bacterial infections are a direct result of amplifications, reductions, or applications in host cellular functions. It is generally known that specific and drastic effects on host cells were caused by even a trace amount of bacterial protein toxins produced by pathogenic bacteria in virulence factors (Fig. 1), and that the bacterial protein toxins act as a causative agent of the major symptoms and precipitating factors of pathologies in bacterial infection. On the other hand, to understand the molecular mechanism by which bacterial protein toxins affect host cell functions is not only the research for pathology of bacterial infection but also the research for cellular biology, and the results of toxin study can bring about the widespread availability of bacterial protein toxins such as highly specific research tools/regents and clinical drugs.
We are studying the molecular mechanisms by which pathogenic bacterial virulence factors affect host cell functions. Our research demonstrated that the receptor of Clostridium perfringens enterotoxin was claudin family which is an essential component of tight junction for intercellular barrier,  Bordetella dermonecrotic toxin (DNT) irreversibly and constitutively activates Rho family proteins by deamidation/polyamination (Fig. 2), and that Pasteurella multocida toxin (PM) bears cysteine protease-like catalytic triad from the structural analysis of its intracellular active region (Fig. 3). In this projects, we aim to analyze their effects on the host at the systemic, tissue, cellular and molecular levels by investigation of the bacterial protein toxins including Bordetella DNT, PMT, CPE, and Escherichia coli cytotoxic necrotizing factor (CNF). We are also analyzing the steric structure and molecular localization of the functional domains of the toxins. In combination, these approaches will help to clarify the structure and function of these bacterial toxins.

horiguchi_e1.jpg Fig. 1: Bacterial protein toxins with various activities that influence particular cellular functions.
Many bacterial protein toxins exert their toxicity by modifying important functions of host cells. The relevant physiological functions of the cells can be determined by dissecting the actions of the bacterial toxins.

horiguchi_j2.jpg Fig. 2: The mechanisms by which Bordetella dermonecrotic toxin (DNT) enters cells and deamidates/polyaminates Rho.
After binding to a putative receptor, DNT is internalized by endocytosis. The toxin undergoes intramolecular cleavage by furin, probably while it is in the endocytotic vesicle, and then enters the cytoplasm by passing across the vesicular membrane. Once in the cytoplasm, DNT deamidates or polyaminates Rho GTPase.

horiguchi_j3.jpg Fig. 3: Overall structure of the intracellular active region of Pasteurella multocida toxin, which is composed of three domains and shows a Trojan horse-like shape.

Some of Recent Papers

  1. Matsuzawa, T., Fukui, A., Kashimoto, T., Nagao, K., Oka, K., Miyake, M., and Horiguchi, Y. (2004). Bordetella dermonecrotic toxin undergoes proteolytic processing to be translocated from a dynamin-related endosome into the cytoplasm in an acidification-independent manner. J. Biol. Chem. 279, 2866-2872.
  2. Miyake, M., Hanajima, M., Matsuzawa, T., Kobayashi, C., Minami, M., Abe, A. and Horiguchi, Y. (2005). Binding of intimin with Tir on the bacterial surface is prerequisite for the barrier disruption induced by enteropathogenic Escherichia coli. Biochem. Biophys. Res. Commun. 337, 922-927.
  3. Miyazawa, M., Kitadokoro, K., Kamitani, S., Shime, H. and Horiguchi, Y. (2006). Crystallization and preliminary crystallographic studies of the Pasteurella multocida toxin catalytic domain. Acta. Crystallograph. Sect. F Struct. Biol. Cryst. Commun., 62, 906-908.
  4. Hanajima-Ozawa, M., Matsuzawa, T., Fukui, A., Kamitani, S., Ohnishi, H., Abe, A., Horiguchi, Y. and Miyake, M. (2007). Enteropathogenic Escherichia coli, Shigella flexneri, and Listeria monocytogenes recruit a junctional protein, zonula occludens-1, to actin tails and pedestals. Infect. Immun., 75, 565-573.
  5. Kitadokoro, K., Kamitani, S., Miyazawa, M., Hanajima-Ozawa, M., Fukui, A., Miyake, M. and Horiguchi, Y. (2007). Crystal structures reveal a thiol protease-like catalytic triad in the C-terminal region of Pasteurella multocida toxin. Proc. Natl. Acad. Sci. U S A. 104, 5139-5144. 104, 5139-5144.
  6. Ohnishi, H., Miyake, M., Kamitani, S., Horiguchi, Y. (2008). The morphological changes in cultured cells caused by Bordetella pertussis adenylate cyclase toxin. FEMS Microbiol. Lett., 279, 174-179.