Ueki Tatsuya, Adachi Takahiro, Kawano Sonoko, Aoshima Masato, Yamaguchi Nobuo, Kanamori Kan, Michibata Hitoshi
Marine Biological Laboratory, Graduate School of Science, Hiroshima University, Mukaishima-cho 2445, 722-0073, Hiroshima, Japan.
Biochim Biophys Acta. 2003 Apr 15;1626(1-3):43-50. doi: 10.1016/s0167-4781(03)00036-8.
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.
自上世纪初以来，人们就知道海鞘的血细胞中积累了高水平的过渡金属钒，尽管这种奇特生物学功能的机制仍然未知。最近，我们从富含钒的海鞘悉尼海鞘（Ascidia sydneiensis samea）含钒血细胞（钒细胞）的细胞质部分中鉴定出三种钒结合蛋白（钒结合素），以前称为钒相关蛋白（VAPs）[动物科学杂志14（1997）37]。在这里，我们描述了钒结合素的克隆、表达及其金属结合能力的分析。两种独立但相关的钒结合素vanabin1和vanabin2的重组蛋白分别与10个和20个钒（IV）离子结合，解离常数分别为2.1×10⁻⁵和2.3×10⁻⁵M。添加铜（II）离子可抑制钒（IV）与这些钒结合素的结合，但镁（II）离子或钼酸盐（VI）离子则无此作用。钒结合素是首个被报道能与钒离子特异性结合的蛋白质；这应该为解决海鞘中钒的选择性积累问题提供线索。
