Biochemical bases of the interaction of human basic fibroblast growth factor with glycosaminoglycans. New insights from trypsin digestion studies.

In the present study we have attempted a characterization of the biochemical bases of the interaction of human basic fibroblast growth factor (bFGF) with glycosaminoglycans (GAGs) in solution. This interaction has been evidenced as the capacity of different GAGs and various sulfated compounds to protect bFGF and different bFGF mutants from tryptic cleavage. Heparin protects bFGF from trypsin digestion in a dose-dependent fashion. Substitution by site-directed mutagenesis of two or more basic residues with neutral glutamine residues in the amino-terminal region bFGF(27-32) or in the carboxyl-terminal region bFGF(118-129) does not significantly affect the protective effect exerted by heparin. In contrast, heparin protection is abolished when the full region bFGF(27-32) is deleted. The capacity of different GAGs to protect bFGF from proteolytic cleavage decreases in the following order: heparin > heparan sulfate > dermatan sulfate = chondroitin sulfates A and C > hyaluronic acid = K5 polysaccharide, indicating that both the degree of sulfation and the backbone structure of GAG modulate its interaction with bFGF. This is confirmed by the different capacity of various sulfated compounds (including dextran sulfates, suramin, trypan blue, and sulfate ion) to protect bFGF from tryptic digestion. Moreover, tryptic digestion studies performed with various heparin molecules and dextran sulfates of different size, ranging from 2.0 kDa to 500 kDa, indicate that the number of bFGF molecules which interact with a single molecule of polysaccharide is related to the molecular mass of the GAG and that six hexose residues are sufficient to protect 1-2 molecules bFGF. In conclusion, our findings indicate that the capacity of GAGs to protect bFGF from tryptic cleavage depends upon their size, sulfation, distribution of the anionic sites along the chain, and structural requirements of the bFGF molecule. These studies will help to design synthetic oligosaccharides endowed with different bFGF agonist and/or antagonist activities.