The Primary Structure of Horseshoe Crab (Tachypleus tridentatus) Coagulogen and its Homologies with Platelet Factor 4

Abstract

Horseshoe crab coagulogen consists of a single basic polypeptide chain having the total 175 amino acid residues. Upon gelation of this protein, a large peptide, named peptide C, which has 28 amino acid residues, was released, and the resulting gel protein consisted of A and B chains, bridged by two disulfide linkages. The sequence studies on peptide C, A chain and B chain provided that their sequences have a significant homology partly with primate fibrinopeptide B and largely with human platelet factor 4. The facts suggest that these are derived from a common ancester or that the coagulogen is a prototype of platelet factor 4. The whole sequence of coagulogen was as follows:Ala-Asp-Thr-Asn-Ala-Pro-Ile-Cys-Leu-Cys-Asp-Glu-Pro-Gly-Val-Leu-Gly-Arg-Thr-Gln-Ile-Val-Thr-Thr-Glu-Ile-Lys-Asp-Lys-Ue-Glu-Lys-Ala-Val-Clu-Ala-Val-Ala-Gln-Glu-Ser-Gly-Val-Ser-Gly-Arg-Cly-Fhe-Ser-Ile-Phe-Ser-His-His-Pro-Val-Phe-Arg-Glu-Cys-Gly-Lys-Tyr-Glu-Cys-Arg-Thr-Val-Arg-Fro-Glu-Hls-Ser-Arg-Cys-Tyr-Asn-Phe-Pro-Pro-Phe-Thr-His-Phe-Lys-Leu-Glu-Cys-Pro-Val-Ser-Thr-Arg-Asp-Cys-Glu-Pro-Va1-Phe-Gly-Tyr-Thr-Va1-Ala-Gly-Glu-Phe-Arg-Va1-1le-Va1-GIn-Ala-Pro-Arg-Ala-Cly-Phe-Arg-GIn-Cys-Val-Trp-Cin-His-Lys-Cys-Arg-Phe-Giy-Ser-Asn-Ser-Cys-Gly-Tyr-Asn-Gly-Arg-Cys-Thr-Gln-Gln-Arg-Ser-Val-Val-Arg-Leu-Val-Thr-Tyr-Asn-Leu-Clu-Lys-Asp-Cly-Phe-Leu-Cys-Glu-Ser-Phe-Arg-Thr-Cys-Gys-Cly-Cys-Pro-Cys-Arg-Ser-Phe,