An apparently higher molecular weight ?-chain variant in a new congenital abnormal fibrinogen Tochigi characterized by the replacement of ? arginine-275 by cysteine

Abstract

A ?-chain variant with an apparently higher molecular weight than the normal ?-chain was detected in a new congenital abnormal fibrinogen with impaired polymerization of the fibrin monomer and with normal release of fibrinopeptides A and B in a 51-year-old male. Purified fibrinogen analyzed on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under the reduced condition in the system of Laemmli contained two protein bands in the ?-chain region (molecular weight, 50,500 as compared with 50,000 for the normal), both with normal crosslinking ability. The presence of two types of ?-chains was more clearly detected when reduced and carboxymethylated fibrinogen was analyzed by SDS-PAGE or when reduced fragment D2 was analyzed on SDS-PAGE followed by Western blotting, and identified by positive staining for anti ?-chain monoclonal antibody. Cyanogen bromide- or lysylendopeptidase-cleavage of purified ?-chains analyzed on reverse-phase high performance liquid chromatography showed the decrease of one peptide compared with the normal and the appearance of an abnormal peptide peak. Amino acid sequence analysis demonstrated that the ? arginine-275 of ?-chain variant was replaced by a cysteine. These data suggest that some regions or conformations containing ?275 will affect the polymerization of fibrin monomers. The propositus' two daughters had the same abnormal fibrinogen. This unique inherited abnormal fibrinogen was designated as fibrinogen Tochigi, and the ?-chain variant as ? Tochigi.