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Pore Formation of Thermostable Direct Hemolysin Secreted from Vibrio parahaemolyticus in Lipid Bilayers

Department of Nutrition and Metabolism, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima, Tokushima, Japan

Toshio Kodama

Department of Bacterial Infections, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan

Kanami Yamashita
Nagakatsu Harada
Masayuki Nakano

Department of Nutrition and Metabolism, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima, Tokushima, Japan

Takeshi Honda

Department of Bacterial Infections, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan

Yutaka Nakaya

Department of Nutrition and Metabolism, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima, Tokushima, Japan

Correspondence: Address correspondence to Akira Takahashi, MD, PhD, Department of Nutrition and Metabolism, Institute of Health Biosciences, The University of Tokushima Graduate School, 3-18-15 Kuramoto-cho, Tokushima City, Tokushima 770-8503, Japan. E-mail:akiratak{at}nutr.med.tokushima-u.ac.jp

Vibrio parahaemolyticus secretes thermostable direct hemolysin (TDH), a major virulence factor. Earlier studies report that TDH is a pore-forming toxin. However, the characteristics of pores formed by TDH in the lipid bilayer, which is permeable to small ions, remain to be elucidated. Ion channel-like activities were observed in lipid bilayers containing TDH. Three types of conductance were identified. All the channels displayed relatively low ion selectivity, and similar ion permeability. The Cl^– channel inhibitors, DIDS, glybenclamide, and NPPB, did not affect the channel activity of pores formed by TDH. R7, a mutant toxin of TDH, also forms pores with channel-like activity in lipid bilayers. The ion permeability of these channels is similar to that of TDH. R7 binds cultured cells and liposomes to a lower extent, compared to TDH. R7 does not display significant hemolytic activity and cell cytotoxicity, possibly owing to the difficulty of insertion into lipid membranes. Once R7 is assembled within lipid membranes, it may assume the same structure as TDH. The authors propose that the single glycine at position 62, substituted with serine in the R7 mutant toxin, plays an important role in TDH insertion into the lipid bilayer.

Key Words: Hemolysin • Ion Permeability • Lipid Bilayer • TDH • Vibrio parahaemolyticus

International Journal of Toxicology, Vol. 25, No. 5, 409-418 (2006)
DOI: 10.1080/10915810600868181


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