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 o f a group of nine polypeptides of relatively similar amino acid sequen ce known as the fibroblast-growth-factor family of proteins. Widely di stributed throughout the organism, fibroblast-growth factors seem to b e involved in numerous physiological processes ranging from control of cell proliferation and differentiation to modulation of animal behavi our and arterial blood pressure. This wide assortment of biological ac tivities explains their involve ment in numerous pathologies. Instabil ity and low yields of the purified protein have precluded high-resolut ion structural studies of the physiological form of aFGF. Nevertheless , modifications introduced recently into the synthesis and purificatio n procedures of this protein have allowed preparations of samples that , as shown here, are reliable substrates to obtain crystals suitable f or X-ray-diffraction studies. These analyses have allowed us to elucid ate the three-dimensional structure of the physiological form of human aFGF by molecular-replacement methods, from the previously reported s tructure of a shortened form of bovine aFGF that was stabilized by poi nt-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 lengt hs and bond angles, respectively. Human aFGF folds according to a beta -trefoil topology. This fold consist of six beta-strand pairs. Three o f 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-te rminus of aFGF up to residue Pro19 appears flexible in the structure a nd does not specifically interact with the rest of the molecule.