title: Sequence variation of Vanabin2-like vanadium-binding proteins in blood cells of the vanadium-accumulating ascidian Ascidia sydneiensis samea.
abstract: The blood cells of ascidians accumulate extremely high levels of the transition metal vanadium. We previously isolated four vanadium-binding proteins (Vanabins 1-4) and a homologous protein (VanabinP) from the vanadium-rich ascidian Ascidia sydneiensis samea. In the present study, we identified cDNAs encoding five different Vanabin2-related proteins in A. sydneiensis samea blood cells. It was notable that the sequences of the encoded proteins vary from that of Vanabin2 at up to 14 specific positions, while both the polypeptide length and the 18 cysteine residues were completely conserved. The most divergent protein, named 14MT, differed from Vanabin2 at all 14 positions. Using immobilized metal-ion affinity chromatography, we found that Vanabin2 and 14MT have the same metal-ion selectivity, but the overall affinity of 14MT for VO(2+) is higher than that of Vanabin2. Binding number for VO(2+) ions was the same between Vanabin2 and 14MT as assessed by gel filtration. These results suggested that sequence variations were under strict evolutionary constraints and high-affinity binding sites for VO(2+) are conserved among Vanabin2 variants.
authors.affiliation: Molecular Physiology Laboratory, Department of Biological Science, Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526, Japan. ueki@hiroshima-u.ac.jp
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Ueki
authors.forename: Makoto
authors.initials: M
authors.lastname: Satake
authors.forename: Kei
authors.initials: K
authors.lastname: Kamino
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Michibata
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001773:Blood Cells / Q000378:metabolism; D001798:Blood Proteins / Q000235:genetics* / Q000378:metabolism; D017124:Conserved Sequence; D003545:Cysteine / Q000737:chemistry; D018076:DNA, Complementary / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D014561:Urochordata / Q000235:genetics* / Q000378:metabolism; D014639:Vanadium / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001798:Blood Proteins; D018076:DNA, Complementary; D014639:Vanadium; D003545:Cysteine