Myo-inositol hexasulphate and low molecular weight heparin binding to human acidic fibroblast growth factor: a calorimetric and FTIR study.

The interaction of an amino-terminal-truncated 139 amino-acids form of human acidic fibroblast growth factor with myo-inositol hexasulphate and low molecular weight (3500 g mol(-1)) heparin has been studied by isothermal titration calorimetry, differential scanning calorimetry and Fourier transform infrared spectroscopy. A slightly higher affinity for the monosaccharide has been measured. The binding of the ligands causes an increase of 13--15 degrees C in the melting temperature of the free protein (45 degrees C). From measured enthalpy and heat capacity changes, calculations of changes in accessible surface areas have been made. These calculations, together with infrared spectroscopy data, indicate that a small conformational change is induced by the binding of both ligands. This conformational change would affect the tertiary structure, not the secondary one.