Human Plasma Fibronectin

Fibronectin (cold-insoluble globulin) is a high molecular weight, adhesive, glycoprotein found in both plasma and the extracellular matrix. Fibronectin is composed of two peptide chains of approximately 275,000 molecular weight which are linked through two interchain disulfide bonds at the COOH-terminal end of the molecule. The structure of fibronectin is characterized by three different types of repeating homologous sequence units. The 45 amino acid type-I repeat constitutes the NH2- and COOH-terminal ends of the protein. The two 60 amino acid type-II segments follow the first nine type-I repeats at the NH2-terminus. The 90 amino acid type-III segments occupy the central region of the fibronectin molecule. Structural differences between plasma and cellular fibronectin as well as between the two subunits of plasma fibronectin have been identified. These differences likely originate due to transcriptional and posttranscriptional events involving mRNA splicing