Primary Structure of Human Fibrinogen

Abstract

Five disulfide‐containing fragments obtained from cyanogen‐bromide‐cleaved human fibrinogen (N‐DSK, Hi2‐DSK, Ho1‐DSK, Ho2‐DSK and Ho3‐DSK) have been characterized in this report. The complete primary structure of the ‘N‐terminal disulfide knot’, N‐DSK, has been elucidated earlier. The individual chains of the fragments composed of more than one chain have been purified following reduction and alkylation. Hi‐2‐DSK, M r 26600, a one‐chain fragment with one intra‐chain disulfide bond is derived from the Aα chain of fibrinogen. Ho1‐DSK, M r 43000, consists of five chains linked together by six disulfide bridges. The largest chain of Ho1‐DSK, M r 21000, is derived from the γ chain of fibrinogen, a smaller chain, M r 5900, from the Aα chain and the three remaining, M r 5800, 4300 and 2200, from the Bβ chain. Ho2‐DSK, M r 5400, is derived from the Bβ chain of fibrinogen and constitutes a single‐chain peptide with one disulfide bond. Ho3‐DSK, M r 7400, consists of two chains connected with one disulfide bridge. Amino acid analysis of the disulfide knots and their individual chains is presented. Partial amino acid sequence of Hi2‐DSK, the four larger chains of Ho1‐DSK and Ho2‐DSK and the complete sequence of the smallest chain of Ho1‐DSK is shown. All disulfide knots except N‐DSK were found to be monomeric. One mole of N‐DSK and two moles of each of the other disulfide knots are present per mole of fibrinogen. These five disulfide knots account for all disulfides in human fibrinogen (fraction 1–4). The location of the disulfide knots in the fibrinogen molecule and the arrangement of the disulfide bonds is discussed.