CRYSTALLIZATION AND X-RAY-INVESTIGATION OF VITAMIN-D-BINDING PROTEIN FROM HUMAN SERUM - IDENTIFICATION OF THE CRYSTAL CONTENT

Vitamin D-binding protein (DBP), a multifunctional, highly polymorphic glycoprotein responsible for the transport of vitamin D and for seque stering extracellular actin, was isolated from human serum and crystal lized using vapour diffusion methods. The crystals were grown from 7.5 % v/v polyethylene glycol 400 and 0.1 M acetate buffer at pH 4.6. Thes e crystals show diffraction patterns consistent with the tetragonal sp ace groups P4(1), and P4(3) with unit cell dimensions a = b = 135.5(4) Angstrom and c =75.9(4) Angstrom. They diffract to 2.3 Angstrom Using polyacrylamide gel electrophoresis it was shown that according to the ir electrophoretic mobility the O-glycosylated isoforms, with a termin al sialic acid residue, are absent in the crystals.