Oligomerization of Escherichia coli enterotoxin b through its C-terminal hydrophobic alpha-helix.
Using a chemical cross-linker and gel electrophoresis or a dot blot overlay assay, we studied protein-protein interaction of STb toxin, a 48-residue amphiphilic polypeptide causing intestinal disorders. For the first time, we report on the oligomerization property of STb. This enterotoxin forms hexamers and heptamers in a temperature-independent fashion in presence or absence of its receptor (sulfatide) anchored in a 50-nm liposome or as a free molecule. Full STb structure integrity is necessary for its oligomerization as this process is not observed under reducing conditions in the presence of beta-mercaptoethanol. STb treatment with tetramethylurea (TMU) and different detergents prevented oligomerization. Site-directed mutagenesis decreasing overall STb hydrophobicity in the hydrophobic alpha-helix resulted in the incapacity to form oligomers. Taken together, these data suggest that the C-terminal hydrophobic alpha-helix corresponds to the domain of STb-STb inter-binding where hydrophobic interaction is involved.
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Groupe de Recherche sur les Maladies Infectieuses du Porc, Département de Pathologie et Microbiologie, Faculté de Médecine Vétérinaire, Université de Montréal, 3200 Sicotte, C.P. 5000, Québec J2S 7C6, Saint-Hyacinthe, Canada.
Harel
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Dubreuil
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JD
D000595:Amino Acid Sequence; D001427:Bacterial Toxins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D003902:Detergents; D004591:Electrophoresis, Polyacrylamide Gel; D004768:Enterotoxins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D008782:Methylurea Compounds; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation
D001427:Bacterial Toxins; D003902:Detergents; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D008782:Methylurea Compounds; C034151:heat stable toxin (E coli); C004168:1,1,3,3-tetramethylurea