cDNA cloning, protein structure modeling of rhesus monkey (Macaca mulatta) prothrombin

Hemorrhagic diseases have been considered to be one of the main causes of xenotransplantation failure. To explore the role of the rhesus monkey (Macaca mulatta) coagulation system in a pig-to-human xenotransplantation model, we primarily studied the full-length cDNA and the three-dimensional (3-D) structures of the important coagulation factor-prothrombin of the rhesus.

The full-length cDNA of rhesus prothrombin was obtained by rhesus monkey liver cDNA library screening and a 5'RACE technique. The 3-D protein structure was modeled using the SWISS-MODEL program. The important macromolecular interaction sites were compared with human and porcine prothrombin.

At first, the full-length rhesus prothrombin cDNA was cloned; the sequence was submitted to the Genebank (accession number: EF057490). The full-length cDNA is 2029 bp, with a complete open reading frame of 1884 bp, coding 626 amino acids. The deduced protein sequence contains a signal peptide, propeptide, Gla domain, two Kringle domains, and a Trypsin domain. The nucleotide similarities of rhesus-human and rhesus-porcine genes are 95.64% and 86.14%, and those of the amino acids, 94.51% and 82.82%, respectively. Some important functional sites, such as the catalytic triad DHS, RGD, Na+ -binding, and the carboxylase-binding site, are highly conserved. However, among the three species some variations are observed in potential N-glycosylation, O-glycosylation, phosphorylation, cleavage site, FXa-binding sites. Especially, the autolysis loop shows great differences in both amino acid sequence and 3-D model.

The great similarity of prothrombin among rhesus, human, and porcine confirmed the great value of the pig-to-rhesus xenotransplantation model. The variation especially in some important recognition sites between rhesus and pig would vary the binding affinity of enzymes to xenosubstrates and their reaction velocities in postoperative coagulation processes, which would be one possible reason for the disordered regulation of clotting seen during the xenorejection in animal models.