Vitronectin exists in two structurally and functionally distinct forms in human plasma.
Vitronectin (serum spreading factor, S-protein or epibolin) is a plasma glycoprotein implicated in cell adhesion, as well as in the regulation of complement-mediated cytolysis and antithrombin III function. Vitronectin was found to exist in fresh human plasma as a heterogeneous mixture consisting of 2% heparin-binding form and the remainder as a non-binding species. Heparin-binding vitronectin consisted of 6.5 S aggregates with a Stokes radius of 5.6 nm, which was enriched in the 65 kDa polypeptide, with a high content of molecules and a putative unfolded conformation. In contrast, non-heparin-binding vitronectin was a 4.2 S monomer with a Stokes radius of 3.9 nm, which appeared to be in a folded conformation with an immunologically cryptic site. Both vitronectins displayed similar activities in mediating the spreading of BHK fibroblastic cells on substrates. During blood coagulation, 5% more of the non-heparin-binding vitronectin was converted into the heparin-binding form, producing a greater than 3.5-fold increase in this species. Our results indicate that vitronectin normally exists in circulating blood in at least two structurally and functionally distinct forms which may serve different functions.
Izumi
M
M
Department of Biology, Ochanomizu University, Tokyo, Japan.
Yamada
K M
KM
Hayashi
M
M
D000906:Antibodies; D015153:Blotting, Western; D004797:Enzyme-Linked Immunosorbent Assay; D006023:Glycoproteins / Q000097:blood*; D006493:Heparin / Q000378:metabolism; D006801:Humans; D011487:Protein Conformation; D019096:Vitronectin
D000906:Antibodies; D006023:Glycoproteins; D019096:Vitronectin; D006493:Heparin