Human vitamin D-binding protein (hDBP), also known as Gcglobulin, is an abundant, multifunctional, and highly polymorphic serum glycoprotein synthesized by the liver1. DBP is the major serum transport protein for the vitamin D sterols2, binds and sequesters monomers of actin with high affinity3, 4, and has been identified on the surface of a variety of cell types including B-lymphocytes5, subpopulations of T-lymphocytes6, and the cytotrophoblasts of the placenta7.
DBP is a secreted protein and would therefore be predicted to have a signal sequence. The amino-terminus of the mature serum protein was established by aligning the sequence predicted by the cDNA to a sequenced amino-terminal hDBP peptide8.
References:
1.Haddad, J. G. 1979. Transport of vitamin D metabolites. Clin. Orthop. Relat. Res. 142:249-274.
2.Daiger, S. P., M. S. Schanfield, and L. L. Cavalli-Sforza. 1975. Group specific component (Gc) proteins bind vitamin D and 25-hydroxyvitamin D. Proc. Natl. Acad. Sci. USA. 72:2076-2080.
3.Cooke, N. E., J. Walgate, and J. G. Haddad. 1979. Human serum binding protein for vitamin D and its metabolites. I. Physicochemical and immunological identification in human tissues. J. Biol. Chem. 254: 5965-5971.
4.Van Baelen, H., R. Bouillon, and P. DeMoor. 1980. Vitamin D binding protein (Gc-Globulin) binds actin. J. Biol. Chem. 255:2270-2272.
5.Petrini, M., D. L. Emerson, and R. M. Galbraith. 1983. Linkage between surface immunoglobulin and cytoskeleton of B lymphocytes may involve Gc protein. Nature (Lond.). 306:73-74.
6.Petrini, M., R. M. Galbraith, D. L. Emerson, A. E. Nel, and P. Arnaud. 1985. Structural studies of T lymphocyte Fc receptors. J. Biol. Chem. 260:1804-1810.
7.Nestler, J. E., E. Lange, J. McLeod, H. J. Kliman, and J. F. Strauss. 1985. Detection of vitamin D binding protein (DBP) in human cytotrophoblasts. Seventh Annual American Societyfor Bone and Mineral Research. Wash. DC. 266a. (Abstr.).
8.Svasti, J., A. Kurosky, A. Bennett, and B. H. Bowman. 1979. Molecular basis for the three major forms of human serum vitamin D binding protein (group specific component). Biochemistry. 18:1611-1617.