Porcine vitronectin, the most compact form of single-chain vitronectin: the smallest molecular mass among vitronectins was ascribed to deletion and substitution of base pairs, and proteolytic trimming of the peptide.

Vitronectin is a multifunctional glycoprotein regulating the fibrinolysis, complement, and coagulation systems in plasma, besides exhibiting cell-spreading activity. Porcine vitronectin has an unusually small molecular mass among the vitronectins hitherto found, which seems to make it hard for it to retain all the known activities. In this study, the complete primary structure of porcine vitronectin was elucidated by cloned cDNA and glycoprotein analyses. A coding sequence of 459 amino acids including a signal peptide of 19 amino acids was deduced from the cDNA. The coding sequence showed 70.3% homology with that of human vitronectin, but porcine vitronectin lacked 22 amino acids in the connecting region. One amino acid substitution resulted in the loss of a potential glycosylation site in accordance with the finding on glycopeptide analyses that porcine vitronectin contained two kinds of glycosylated sequences, while human vitronectin contained three. C-Terminal analysis of porcine vitronectin indicated that an 80 amino acid fragment was completely removed from the C-terminal end on proteolytic processing. Thus, porcine vitronectin only exists in a truncated single-chain form representing the most compact functional form of vitronectin, which suggests the lack of functional necessity of the truncated C-terminal fragment.

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