Yoshihara Masao, Ueki Tatsuya, Watanabe Takahiro, Yamaguchi Nobuo, Kamino Kei, Michibata Hitoshi
Molecular Physiology Laboratory, Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526, Japan.
Biochim Biophys Acta. 2005 Sep 25;1730(3):206-14. doi: 10.1016/j.bbaexp.2005.07.002.
Some ascidians accumulate high levels of the transition metal vanadium in their blood cells. The process of vanadium accumulation has not yet been elucidated. In this report, we describe the isolation and cDNA cloning of a novel vanadium-binding protein, designated as VanabinP, from the blood plasma of the vanadium-rich ascidian, Ascidia sydneiensis samea. The predicted amino acid sequence of VanabinP was highly conserved and similar to those of other Vanabins. The N-terminus of the mature form of VanabinP was rich in basic amino acid residues. VanabinP cDNA was originally isolated from blood cells, as were the other four Vanabins. However, Western blot analysis revealed that the VanabinP protein was localized to the blood plasma and was not detectable in blood cells. RT-PCR analysis and in situ hybridization indicated that the VanabinP gene was transcribed in some cell types localized to peripheral connective tissues of the alimentary canal, muscle, blood cells, and a portion of the branchial sac. Recombinant VanabinP bound a maximum of 13 vanadium(IV) ions per molecule with a Kd of 2.8 x 10(-5) M. These results suggest that VanabinP is produced in several types of cell, including blood cells, and is immediately secreted into the blood plasma where it functions as a vanadium(IV) carrier.
一些海鞘在其血细胞中积累高水平的过渡金属钒。钒的积累过程尚未阐明。在本报告中，我们描述了从富含钒的海鞘悉尼海鞘（Ascidia sydneiensis samea）的血浆中分离并克隆一种新型钒结合蛋白，命名为VanabinP。VanabinP的预测氨基酸序列高度保守，与其他钒结合蛋白相似。成熟形式的VanabinP的N端富含碱性氨基酸残基。VanabinP cDNA最初是从血细胞中分离出来的，其他四种钒结合蛋白也是如此。然而，蛋白质印迹分析表明，VanabinP蛋白定位于血浆中，在血细胞中无法检测到。逆转录聚合酶链反应（RT-PCR）分析和原位杂交表明，VanabinP基因在位于消化道外周结缔组织、肌肉、血细胞和鳃囊一部分的某些细胞类型中转录。重组VanabinP每个分子最多结合13个钒（IV）离子，解离常数（Kd）为2.8×10^(-5) M。这些结果表明，VanabinP在包括血细胞在内的几种细胞类型中产生，并立即分泌到血浆中，在那里它作为钒（IV）载体发挥作用。
