[Fibronectin--synergy cell recognition site].

Fibronectin is a major and multifunctional cell adhesive extracellular matrix protein. Many studies have been carried out to reveal its structures and functions. One of the most important question was the cell adhesive structures on the molecule and how to associate with cell surface receptors. It was striking that very short amino acid sequence Arg-Gly-Asp (RGD) in the central cell binding domain of fibronectin was determined as minimum cell adhesive sequence. However, other data indicate that additional subregions besides the RGD motif are required for its cell adhesive activity mediated by alpha 5 beta 1 fibronectin receptor. This putative synergistic site, second site, was analyzed by site directed mutagenesis studies, homology scanning using intramolecular chimeras and epitope mapping using inhibitory monoclonal antibodies. Those studies cleared that the functional sequence, Pro-His-Ser-Arg-Asn (PHSRN), synergistically enhances the cell-adhesive activity of RGD motif depends on the activation state of the integrin.