A comparative study of partial primary structures of the catalytic region of mammalian protein C

Protein C (PROC) is a plasma vitamin K-dependent zymogen of a serine protease which regulates blood-clotting cascade through proteolytic inactivation of the non-enzymatic cofactors of blood coagulation, Va and VIIIa. We characterized the partial nucleotide and amino acid sequences for the catalytic domain of PROC in six mammalian species, rhesus monkey, dog, cat, goat, horse and mouse, and compared these sequences with known ones from humans, the bovine and rat. By using a pair of primers based on the nucleotide sequences from human and bovine PROC cDNA, the PROC gene fragments were enzymatically amplified from their genomic DNAs and were sequenced by the dideoxy-termination method. The cloned PROC gDNA encoded a part of the heavy chain of PROC including the lesions of active site residues corresponding to human PROC Asp-257 and Ser-360. Comparison of the sequences from these species revealed that there was a high degree of homology at the nucleotide and amino acid levels; from 69% to 96% of the amino acids in the catalytic region were identical among the nine species including humans, the bovine and rat. The locations of five Cys residues as well as the putative carbohydrate attachment sites were evolutionally conserved. All the amino acids recognized in the human abnormal PROC variants were conserved across species, suggesting their functional importance, and a comparison of the conserved residues among PROC from multiple species will provide considerable information in the investigations of PROC functions.