J. Biol. Chem., Vol. 265, Issue 17, 9778-9781, 06, 1990
The presence of methionine or threonine at position 381 in vitronectin is correlated with proteolytic cleavage at arginine 379
DM Tollefsen, CJ Weigel and MH Kabeer
Department of Medicine, Washington University, St. Louis, Missouri 63110.
Vitronectin (serum spreading factor, complement S protein, epibolin) is a
glycoprotein that mediates cell adhesion and interacts with components of
the complement, coagulation, and fibrinolytic systems. It circulates in
plasma as a 75-kDa single chain polypeptide and as a two- chain form
consisting of 65- and 10-kDa polypeptides linked by a disulfide bond. An
individual may have a predominance of the single chain or the two-chain
form inherited as a Mendelian trait or have approximately equal amounts of
both forms. Inspection of published cDNA sequences suggests that either
methionine or threonine can occur at position 381, which is adjacent to the
presumed site of proteolytic cleavage (Arg379-Ala380) that gives rise to
the two-chain form. We have determined the presence of the Met381 and/or
Thr381 alleles of the vitronectin gene in 42 individuals by oligonucleotide
hybridization to genomic DNA. To determine whether this polymorphism is
correlated with the susceptibility to cleavage of the Arg379-Ala380 peptide
bond in vivo, we have prepared immunoblots of plasma from the same group of
individuals. Nineteen individuals homozygous for the Thr381 allele had 17
+/- 9% (mean +/- S.D.) single chain vitronectin in their plasma samples.
Nine individuals homozygous for the Met381 allele had 66 +/- 4% single
chain vitronectin. Fourteen heterozygous individuals had 38 +/- 13% single
chain vitronectin. The differences in mean values were statistically
significant (p less than 0.001). These results suggest that the presence of
threonine rather than methionine at position 381 of vitronectin increases
the susceptibility of the protein to cleavage of the Arg379-Ala380 peptide
bond in vivo.