Expression of a recombinant baculovirus for vitronectin in insect cells: purification, characterization of post-translational modifications and functional studies of the recombinant protein.

Vitronectin (VN) is a cell attachment glycoprotein present in plasma and the extracellular matrix that also has multiple regulatory roles in the complement, coagulation, and fibrinolytic systems. VN stabilizes plasminogen activator inhibitor-1 (PAI-1) with potential binding sites reported at both the somatomedin B and heparin binding domains. In order to perform detailed structure-function analyses of VN, we have produced and expressed a recombinant baculovirus containing the cDNA of human VN. Recombinant VN (rVN) was secreted as a single chain 70-kDa protein into the serum-free culture medium of infected Spodoptera frugiperda cells. Maximum rVN levels of 33.9 mg/liter were obtained 48 hours post-infection. Purification of rVN from serum-free medium was achieved with single-step anion-exchange chromatography. Several native post-translational modifications were demonstrated in rVN including the presence of N-linked oligosaccharides, tyrosine sulfation, and serine phosphorylation. Recombinant VN retained cell and PAI-1 binding capacity. Therefore, rVN expressed for the first time in insect cells retains many post-translational modifications and functional activities and will be useful for additional structure-function analyses.