Characterization of a novel vanadium-binding protein (VBP-129) from blood plasma of the vanadium-rich ascidian Ascidia sydneiensis samea.
The ascidians, the so-called sea squirts, accumulate high levels of vanadium, a transition metal. Since Henze first observed this physiologically unusual phenomenon about one hundred years ago, it has attracted interdisciplinary attention from chemists, physiologists, and biochemists. The maximum concentration of vanadium in ascidians can reach 350 mM, and most of the vanadium ions are stored in the +3 oxidation state in the vacuoles of vanadium-accumulating blood cells known as vanadocytes. Many proteins involved in the accumulation and reduction of vanadium in the vanadocytes, blood plasma, and digestive tract have been identified. However, the process by which vanadium is taken in prior to its accumulation in vanadocytes has not been elucidated. In the present study, a novel vanadium-binding protein, designated VBP-129, was identified from blood plasma of the vanadium-rich ascidian Ascidia sydneiensis samea. Although VBP-129 mRNA was transcribed in all A. sydneiensis samea tissues examined, the VBP-129 protein was exclusively localized in blood plasma and muscle cells of this ascidian. It bound not only to VO(2+) but also to Fe(3+), Co(2+), Cu(2+), and Zn(2+); on the other hand, a truncated form of VBP-129, designated VBP-88, bound only to Co(2+), Cu(2+) and Zn(2+). In a pull-down assay, an interaction between VanabinP and VBP-129 occurred both in the presence and the absence of VO(2+). These results suggest that VBP-129 and VanabinP function cooperatively as metallochaperones in blood plasma.
Molecular Physiology Laboratory, Department of Biological Science, Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima 739-8526, Japan.
Masao
M
Yoshihara
Tatsuya
T
Ueki
Nobuo
N
Yamaguchi
Kei
K
Kamino
Hitoshi
H
Michibata
D000595:Amino Acid Sequence; D000818:Animals; D001798:Blood Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D015870:Gene Expression; D008969:Molecular Sequence Data; D014561:Urochordata / Q000235:genetics / Q000378:metabolism*; D014639:Vanadium / Q000378:metabolism*
D001798:Blood Proteins; D018076:DNA, Complementary; D014639:Vanadium