Abstract

The cDNA sequence of the B chain of thrombin (EC 3.4.21.5) has been determined from nine vertebrate species (rat, mouse, rabbit, chicken, gecko, newt, rainbow trout, sturgeon, and hagfish). The amino acid sequence identities vary from 96.5% (rat vs. mouse) to 62.6% (newt vs. hagfish). Of the 240 amino acids spanned in all the species compared, there is identity at 110 (45.8%) positions. When conservative changes are included, the amino acid similarity increases to 75%. The most conserved portions of the B chain are the active-site residues and adjacent amino acids, the B loop, and the primary substrate-binding region. In addition, the Arg-Gly-Asp motif is conserved in 9 of the 11 species compared, and the chemotactic/growth factor domain is well conserved in all of the 11 species compared. The least conserved regions of the B chain correspond to surface loops, including the putative thrombomodulin-binding sites and one of the hirudin-binding regions. The extent of the amino acid sequence similarity and the conservation of many of the functional/structural motifs suggests that, in addition to their role in blood coagulation, vertebrate thrombins may also play an important role in the general mechanisms of wound repair.