On the identity of vitronectin and S-protein: immunological crossreactivity
and functional studies
BR Tomasini and DF Mosher
Vitronectin (serum spreading factor), a major serum cell adhesion molecule,
was compared with S-protein, the inhibitor of the C5-9 membrane attack
complex. Data from the literature indicate that S- protein and vitronectin
are alpha globulins with the same aminoterminal residues, amino acid
compositions, and concentrations in normal plasma (150 to 250
micrograms/mL). Both proteins have been reported to interact with the
thrombin-antithrombin complex. The cDNA sequences of vitronectin and
S-protein were recently determined and found to be almost identical. In the
present studies, rabbit-anti-S-protein and a monoclonal antibody to
vitronectin both recognized 65,000- and 75,000- molecular weight (mol wt)
polypeptides when plasma or serum proteins were separated by sodium dodecyl
sulfate-polyacrylamide gel electrophoresis and transferred to
nitrocellulose paper. The 65,000 and 75,000-mol wt polypeptides bound more
avidly from serum than plasma to monoclonal anti-vitronectin or heparin
coupled to agarose. The presence or absence of the polypeptides constituted
a major difference between the heparin-binding proteins of serum and
plasma. When complement- activated serum and unactivated serum were
separated by gel filtration, vitronectin coeluted with C9 in high-mol-wt
fractions of activated serum but not unactivated serum. Purified S-protein
was recognized by the monoclonal antibody to vitronectin and promoted
spreading of human skin fibroblasts. Both vitronectin and S-protein were
degraded by thrombin. On the basis of immunological and functional, as well
as biochemical, properties, therefore, S-protein and vitronectin are the
same.
Volume 68,
Issue 3,
pp. 737-742,
09/01/1986
Copyright © 1986 by The American Society of Hematology
