Phosphorylation of vitronectin by a protein kinase in human plasma. Identification of a unique phosphorylation site in the heparin-binding domain

• Published in: The Journal of biological chemistry 1988-02, Vol.263 (4), p.1942-1945
• Main Authors: McGuire, E A, Peacock, M E, Inhorn, R C, Siegel, N R, Tollefsen, D M
• Format: Article
• Language: English
• Subjects: Analytical, structural and metabolic biochemistry; Binding Sites; Biological and medical sciences; Blood Proteins - metabolism; Fundamental and applied biological sciences. Psychology; Glycoproteins; Glycoproteins - blood; heparin; Heparin - metabolism; Humans; man; Peptide Mapping; Phosphorylation; Phosphoserine - analysis; plasma; Protein Kinases - blood; Proteins; Vitronectin
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(19)77969-1

Incubation of human plasma with 27 nM [gamma-32P]ATP in the presence of 20 mM MnCl2 results in the phosphorylation of several proteins detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. About 60% of the incorporated radioactivity is found in a 75-kDa protein containing [32P] phosphoserine. The amino-terminal amino acid sequence of the purified 75-kDa [32P]phosphoprotein is identical to that of vitronectin (also termed serum spreading factor or complement S protein). Rabbit antiserum against vitronectin precipitates greater than 90% of the 75-kDa [32P]phosphoprotein from plasma. Reverse phase chromatography of [32P]vitronectin degraded sequentially with CNBr and chymotrypsin yields one major labeled peptide. The sequence of the peptide, Ser-Arg-Arg-Pro-[32PO4]Ser-Arg-Ala-Thr, corresponds to residues 374-381 which are located in the heparin-binding fragment of vitronectin identified by Suzuki et al. [1984) J. Biol. Chem. 259, 15307-15314). Vitronectin could potentially be phosphorylated in vivo with ATP released from injured cells or secreted by platelets activated during hemostasis.