Structure and function of fibroblast growth factor.

We describe some structural requirements of the fibroblast growth factor (FGF) signaling system for the stimulation of the mitogenic response in terms of the design, synthesis and mitogenic activity of linear peptides related to the human FGF-1 sequence and the structural requirements of heparin for the potentiation of the mitogenic activity of FGF-1. The best mitogenic peptide we have synthesized so far is Ac-WFVGLKKNGSSKRGPRT-NH2, that has been shown: 1) to bind to heparin-Sepharose columns with moderate affinity, requiring about 0.5 M NaCl to be eluted from the resin; 2) to be mitogenic upon BALB/c 3T3 fibroblasts in culture (ED50 = 10-20 microM) and 3) to compete with human FGF-1 for cellular binding (ID50 = 30-50 microM). The potentiating activity of heparin upon FGF-1 has shown to be dependent on the oligosaccharide size, degree of sulfation and carboxylation. Apparently, these same requirements hold for the heparan sulfate molecules. Based on the reported studies, we propose some important requirements of an oligosaccharide to potentiate FGF-1 mitogenic activity: 1) to have a minimum of twelve units, organized as disaccharides where one of the units is a uronic acid and the second is glycosamine; 2) to have at least one iduronic acid sulfated at position 2 and 3) to have N-sulfated glycosamines, preferentially 6-O-sulfated. To have groups of negative charges is not enough: they need to be localized in a correct conformation.