Pore formation of thermostable direct hemolysin secreted from Vibrio parahaemolyticus in lipid bilayers.
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.
Takahashi
Akira
A
Department of Nutrition and Metabolism, Institute of Health Biosciences, The University of Tokushima Graduate School, Tokushima, Tokushima, Japan. akiratak@nutr.med.tokushima-u.ac.jp
Yamamoto
Chiyo
C
Kodama
Toshio
T
Yamashita
Kanami
K
Harada
Nagakatsu
N
Nakano
Masayuki
M
Honda
Takeshi
T
Nakaya
Yutaka
Y
D001427:Bacterial Toxins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D018938:Caco-2 Cells; D002463:Cell Membrane Permeability / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D004847:Epithelial Cells / Q000187:drug effects / Q000502:physiology; D005998:Glycine / Q000737:chemistry; D006460:Hemolysin Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D008051:Lipid Bilayers / Q000378:metabolism; D008081:Liposomes / Q000737:chemistry; D014736:Vibrio parahaemolyticus
D001427:Bacterial Toxins; D006460:Hemolysin Proteins; D008051:Lipid Bilayers; D008081:Liposomes; C068489:thermostable direct hemolysin; D005998:Glycine