Structural relatedness of kappa-casein and fibrinogen gamma-chain.

kappa-Caseins, involved in the milk clotting process, and human fibrinogen gamma-chain, involved in the blood clotting process, show structural similarities. Several long kappa-casein sections, together corresponding to 80% of the whole protein molecule, have their counterparts in the gamma-chain of fibrinogen, in that 31--42% of the amino acid residues occupy identical positions. The section of kappa-casein which contains the chymosin-sensitive bond has a counterpart not only in the gamma but also in the Bbeta-chain of fibrinogen. Furthermore, the secondary structures of the kappa-caseins and of the gamma-chain predicted according to the method of Chou and Fasman present several common features.