X-RAY STRUCTURE OF THE 154-AMINO-ACID FORM OF RECOMBINANT HUMAN BASICFIBROBLAST GROWTH-FACTOR - COMPARISON WITH THE TRUNCATED 146-AMINO-ACID FORM

The crystal structure of the 154-amino-acid form of human basic fibrob last growth factor (hbFGF154), probably representing the intact form o f hbFGF as deduced from the open reading frame of hbFGF cDNA, was dete rmined by X-ray crystallography and refined to a crystallographic resi dual of 19.0% for all data between 20.0 and 2.0 Angstrom resolution. C rystals were obtained from recombinant hbFGF154 expressed in E. coli. hbFGF154 has the same overall structure as the N-terminus truncated 14 6-amino-acid form. The structure has a Kunitz-type fold and is built o f 12 beta-strands of which six antiparallel strands form a beta-sheet barrel. In the structure it was possible to locate two additional resi dues at the N terminus and the last three C-terminal amino-acid residu es, which seem to be disordered in all but one of the reported structu res of the truncated form of hbFGF. The C-terminal amino-acid residues are part of the last beta-strand through the formation of a hydrogen bond between the main-chain amide group of Ala152 and the carbonyl O a tom of Pro28. An apparent phosphate ion is bound within the basic regi on on the surface of the molecule and has as ligands the side chains o f Asn35, Arg128 and Lys133 and two water molecules. A slightly differe nt hydrogen-bonding pattern to the phosphate ion is observed as compar ed with the sulfate ions in the truncated forms [Eriksson, Cousens & M atthews (1993). Protein Sci. 2, 1274-1284; Zhang, Cousens, Barr & Spra ng (1991). Proc. Natl Acad. Sci. USA, 88, 3446-3450]. One molecule of beta-mercaptoethanol forms a disulfide bridge to Cys77.