title: Sugar-binding sites of the HA1 subcomponent of Clostridium botulinum type C progenitor toxin.
abstract: Clostridium botulinum type C 16S progenitor toxin contains a hemagglutinin (HA) subcomponent, designated HA1, which appears to play an important role in the effective internalization of the toxin in gastrointestinal epithelial cells and in creating a broad specificity for the oligosaccharide structure that corresponds to various targets. In this study, using the recombinant protein fused to glutathione S-transferase, we investigated the binding specificity of the HA1 subcomponent to sugars and estimated the binding sites of HA1 based on X-ray crystallography and soaking experiments using various sugars. N-Acetylneuraminic acid, N-acetylgalactosamine, and galactose effectively inhibited the binding that occurs between glutathione S-transferase-HA1 and mucins, whereas N-acetylglucosamine and glucose did not inhibit it. The crystal structures of HA1 complex with N-acetylneuraminic acid, N-acetylgalactosamine, and galactose were also determined. There are two sugar-binding sites, sites I and II. Site I corresponds to the electron densities noted for all sugars and is located at the C-terminal beta-trefoil domain, while site II corresponds to the electron densities noted only for galactose. An aromatic amino acid residue, Trp176, at site I has a stacking interaction with the hexose ring of the sugars. On the other hand, there is no aromatic residue at site II; thus, the interaction with galactose seems to be poor. The double mutant W176A at site I and D271F at site II has no avidity for N-acetylneuraminic acid but has avidity for galactose. In this report, the binding specificity of botulinum C16S toxin HA1 to various sugars is demonstrated based on its structural features.
authors.affiliation: Department of Applied Biological Science, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan.
authors.forename: Toshio
authors.initials: T
authors.lastname: Nakamura
authors.forename: Takashi
authors.initials: T
authors.lastname: Tonozuka
authors.forename: Azusa
authors.initials: A
authors.lastname: Ide
authors.forename: Takayuki
authors.initials: T
authors.lastname: Yuzawa
authors.forename: Keiji
authors.initials: K
authors.lastname: Oguma
authors.forename: Atsushi
authors.initials: A
authors.lastname: Nishikawa
mesh_terms: D000595:Amino Acid Sequence; D003014:Clostridium botulinum / Q000737:chemistry / Q000378:metabolism; D047968:Clostridium botulinum type C / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D006388:Hemagglutinins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009077:Mucins / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D006388:Hemagglutinins; D009077:Mucins; D011993:Recombinant Fusion Proteins