CLONING OF THE COMPLETE CODING SEQUENCE OF RAT FIBRINOGEN B-BETA CHAIN CDNA - INTERSPECIES CONSERVATION OF FIBRIN BETA-15-42 PRIMARY STRUCTURE

After thrombin cleavage, the newly exposed NH2-termini of the beta cha ins play a role in both fibrin polymerization and fibrin interactions with cells in the process of wound healing. These physiological respon ses have been shown to be mediated, at least in part, by beta 15-42. T o compare the sequence of the beta chain of fibrin across species, the complete coding sequence of the rat fibrinogen B beta chain cDNA was cloned (designated pRB beta 3) and characterized. The sequence newly d etermined from pRB beta 3 encompassed nucleotides 121-589, encoding re sidues 9-165 of the mature polypeptide. Significant homology of pRB be ta 3 cDNA and deduced amino acid sequences was found when compared wit h other species' B beta chains. The rat B beta-Arg14-Gly15 thrombin cl eavage site is conserved; however, the fibrinopeptide B sequences are only 50% similar when rat is compared with human. In contrast, the bet a 15-42 region is 100% similar when allowing for conservative amino ac id substitutions. Monoclonal antibodies (MAbs) specific for human fibr inogen B beta 1-21 (1-8C6) and human fibrin beta 15-21 (59D8 and T2G1) failed to cross-react with rat fibrinogen or fibrin by ELISA, respect ively, even though thrombin conversion of rat fibrinogen to fibrin was confirmed. MAb 1-8C6 reacted with reduced and denatured human fibrino gen B beta chain by Western blotting, whereas, MAb T2G1 did not blot w ith reduced and denatured human fibrin beta chain. A comparative analy sis of the binding affinity of the human B beta fibrin(ogen) specific MAbs with B beta fibrin(ogen) from several species suggested that amin o acid residues preceding and including Arg14-Gly15 are important in t he epitope of the B beta 1-21 specific MAb 1-8C6, and that residues Gl y15, Leu19 and/or Lys21 play an important role in the epitope shared b y the beta 15-21-specific MAbs T2G1 and 59D8.