title: Toxic and nontoxic components of botulinum neurotoxin complex are evolved from a common ancestral zinc protein.
abstract: Zinc atoms play an essential role in a number of enzymes. Botulinum neurotoxin (BoNT), the most potent toxin known in nature, is a zinc-dependent endopeptidase. Here we identify the nontoxic nonhemagglutinin (NTNHA), one of the BoNT-complex constituents, as a zinc-binding protein, along with BoNT. A protein structure classification database search indicated that BoNT and NTNHA share a similar domain architecture, comprising a zinc-dependent metalloproteinase-like, BoNT coiled-coil motif and concanavalin A-like domains. Inductively coupled plasma-mass spectrometry analysis demonstrated that every single NTNHA molecule contains a single zinc atom. This is the first demonstration of a zinc atom in this protein, as far as we know. However, the NTNHA molecule does not possess any known zinc-coordinating motif, whereas all BoNT serotypes possess the classical HEXXH motif. Homology modeling of the NTNHA structure implied that a consensus K-C-L-I-K-X(35)-D sequence common among all NTNHA serotype molecules appears to coordinate a single zinc atom. These findings lead us to propose that NTNHA and BoNT may have evolved distinct functional specializations following their branching out from a common ancestral zinc protein.
authors.affiliation: Department of Food and Cosmetic Science, Faculty of Bioindustry, Tokyo University of Agriculture, Abashiri, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Inui
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Sagane
authors.forename: Keita
authors.initials: K
authors.lastname: Miyata
authors.forename: Shin-Ichiro
authors.initials: S
authors.lastname: Miyashita
authors.forename: Tomonori
authors.initials: T
authors.lastname: Suzuki
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Shikamori
authors.forename: Tohru
authors.initials: T
authors.lastname: Ohyama
authors.forename: Koichi
authors.initials: K
authors.lastname: Niwa
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Watanabe
mesh_terms: D000595:Amino Acid Sequence; D001905:Botulinum Toxins / Q000737:chemistry* / Q000235:genetics / Q000633:toxicity*; D006388:Hemagglutinins / Q000737:chemistry / Q000235:genetics / Q000633:toxicity; D008969:Molecular Sequence Data; D005810:Multigene Family; D009498:Neurotoxins / Q000737:chemistry* / Q000235:genetics / Q000633:toxicity*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D015032:Zinc / Q000737:chemistry*
chemical_list: D006388:Hemagglutinins; D009498:Neurotoxins; D001905:Botulinum Toxins; D015032:Zinc