title: Vanadium-binding proteins (vanabins) from a vanadium-rich ascidian Ascidia sydneiensis samea.
abstract: Since the beginning of the last century, it has been known that ascidians accumulate high levels of a transition metal, vanadium, in their blood cells, although the mechanism for this curious biological function remains unknown. Recently, we identified three vanadium-binding proteins (vanabins), previously denoted as vanadium-associated proteins (VAPs) [Zool. Sci. 14 (1997) 37], from the cytoplasm fraction of vanadium-containing blood cells (vanadocytes) of the vanadium-rich ascidian Ascidia sydneiensis samea. Here, we describe the cloning, expression, and analysis of the metal-binding ability of vanabins. Recombinant proteins of two independent but related vanabins, vanabin1 and vanabin2, bound to 10 and 20 vanadium(IV) ions with dissociation constants of 2.1x10(-5) and 2.3x10(-5) M, respectively. The binding of vanadium(IV) to these vanabins was inhibited by the addition of copper(II) ions, but not by magnesium(II) or molybdate(VI) ions. Vanabins are the first proteins reported to show specific binding to vanadium ions; this should provide a clue to resolving the problem regarding the selective accumulation of vanadium in ascidians.
authors.affiliation: Marine Biological Laboratory, Graduate School of Science, Hiroshima University, Mukaishima-cho 2445, 722-0073, Hiroshima, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Ueki
authors.forename: Takahiro
authors.initials: T
authors.lastname: Adachi
authors.forename: Sonoko
authors.initials: S
authors.lastname: Kawano
authors.forename: Masato
authors.initials: M
authors.lastname: Aoshima
authors.forename: Nobuo
authors.initials: N
authors.lastname: Yamaguchi
authors.forename: Kan
authors.initials: K
authors.lastname: Kanamori
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Michibata
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D016384:Consensus Sequence; D008670:Metals / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D014561:Urochordata / Q000378:metabolism*; D014639:Vanadium / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D008670:Metals; D014639:Vanadium