Structure Of Plasma Fibronectin. Gene Multiplication

Abstract

Plasma fibronectin (cold insoluble globulin) is a multiple domain glycoprotein composed of two nearly identical disulphide bridged polypeptide chains with molecular weight of 220,000. It is a substrate for factor XIIIa and binds to gelatin and heparin. After digestion of bovine fibronectin with plasmin, four fragments with Mr 29,000, 170,000, 23,000 and 6,000 have been isolated. The N-terminal 29,000 Mr fragment (259 residues) has 10 disulphide bridges within five mutually homologous domains, called “fingers”. The sequence <Gln-Ala-Gln-Gln-Ile-Val-Gln-Pro-Gln- contains the acceptor site for factor XIIIa at position 3. The 170,000 Mr fragment contains both the gelatin and the heparin binding site. After further digestion with chymotrypsin a fragment (Mr 45,000) which binds to gelatin, and a fragment (Mr 30,000) which binds to heparin, have been isolated. The Mr 45,000 fragment consists of at least one more “finger” plus two other mutually homologous domains each with two disulphide bridges. The 23,000 Mr fragment (178 residues) consists of three “finger“- domains and has an N-terminal sequence Val-Arg-. The Mr 6,000 (C-terminal fragment) is a dimer of two identical 26-residue peptides linked by two disulphide bridges. 820 of the expected approx. 1800 residues have been placed in sequence.