X-ray structure of native full-length human fibroblast-growth factor at 0.25-nm resolution

Acidic fibroblast-growth factor (aFGF) is one of the typical members of a group of nine polypeptides of relatively similar amino acid sequence known as the fibroblast-growth-factor family of proteins. Widely distributed throughout the organism, fibroblast-growth factors seem to be involved in numerous physiological processes ranging from control of cell proliferation and differentiation to modulation of animal behaviour and arterial blood pressure. This wide assortment of biological activities explains their involvement in numerous pathologies. Instability and low yields of the purified protein have precluded high-resolution structural studies of the physiological form of aFGF. Nevertheless, modifications introduced recently into the synthesis and purification procedures of this protein have allowed preparations of samples that, as shown here, are reliable substrates to obtain crystals suitable for X-ray-diffraction studies. These analyses have allowed us to elucidate the three-dimensional structure of the physiological form of human aFGF by molecular-replacement methods, from the previously reported structure of a shortened form of bovine aFGF that was stabilized by point-directed mutagenesis. The structure was refined at a resolution of 0.25 nm to an R factor of 20.4% for 13,109 reflections between 0.6 nm and 0.25 nm, with rmsd of 1.1 pm and 1.9 degrees from ideal bond lengths and bond angles, respectively. Human aFGF folds according to a beta-trefoil topology. This fold consist of six beta-strand pairs. Three of them form a six-stranded beta-barrel structure that is capped at one end by the other three pairs arranged in a triangular array. The N-terminus of aFGF up to residue Pro19 appears flexible in the structure and does not specifically interact with the rest of the molecule.