The binding of fibronectin to entactin is mediated through the 29 kDa amino terminal fragment of fibronectin and the G2 domain of entactin.

Previous work has shown that fibronectin and entactin, an ubiquitous basement membrane glycoprotein, co-localize in the extracellular matrix of the embryonal carcinoma-derived 4CQ cell. Glutathione-S-transferase (GST) fusion proteins containing different domains of entactin have been obtained in the pGEX3X expression vector. These fusion proteins, GST-G1, GST-G2, GST-E and GST-G3, were purified with a glutathione affinity column. By using a solid phase binding assay, it was shown that the 125I-labeled 29 kDa amino terminal fragment of bovine fibronectin bound specifically to the immobilized GST-G2 fusion protein but not to GST-G1, GST-E, and GST-G3. Half saturation for binding of the 29 kDa fibronectin fragment to the immobilized GST-G2 fusion protein was obtained at a concentration of approximately 5 nM. It is suggested that the strong association between GST-G2, which contains the second globular domain of entactin, and the 29 kDa amino terminal fragment of fibronectin may be involved in the assembly of certain types of extracellular matrices.