Recombinant Human Fibrinogen and Sulfation of the β′ Chain

Human fibrinogen and the homodimeric γ′-chain-containing variant have been expressed in BHK cells using cDNAs coding for the α, β, and γ (or γ′) chains. The fibrinogens were secreted at levels greater than 4 μg (mg of total cell protein)⁻¹ day⁻¹ and were biologically active in clotting assays. Recombinant fibrinogen containing the γ′ chain incorporated ³⁵SO₄ into its chains during biosynthesis, while no incorporation occurred in the protein containing the γ chain. The identity of the sulfated γ′ chain was verified by its ability to form dimers during clotting. In addition, carboxypeptidase Y digestion of the recombinant fibrinogen containing the γ′ chain released 96% of the ³⁵S label from the sulfated chain, and the radioactive material was identified as tyrosine O-sulfate. These results clarify previous findings of the sulfation of tyrosine in human fibrinogen.