Structural basis for the species selectivity of a fibrin-specific monoclonal antibody

The structural determinant underlying the species specificity of a monoclonal anti-fibrin antibody (59D8) is the leucyl residue at position 5 in beta-chains of human fibrin. Anti-fibrin antibody 59D8 which had been elicited by immunization with human beta(1-7) peptide, Gly-His-Arg-Pro-Leu-Asp-Lys, binds to human and canine fibrins but not to bovine, ovine, or porcine fibrins. A comparison of the available amino acid sequence data suggested that the ability of anti-fibrin antibody 59D8 to discriminate among various fibrin beta-chains might be due to the amino acid at position 5. This was confirmed by competitive inhibition studies using synthetic fibrin-like peptides and determination of the amino acid sequences of the N-termini of ovine and porcine fibrin beta-chains. Edman degradation employing o-phthalaldehyde blocking permitted use of fibrin monomer rather than its separated constituent polypeptide chains. The same sequencing strategy was used to obtain partial sequence data for the alpha-chains of bovine, ovine, and porcine fibrin.