Hints of nonhierarchical folding of acidic fibroblast growth factor.
We have analyzed by circular dichroism (CD) and proton nuclear magnetic resonance (NMR) the helical propensity of the all-beta protein acidic fibroblast growth factor (aFGF) and two peptides corresponding to beta-strand 8 (beta8 peptide, amino acids 95-107) and the beta-strand 8/turn/beta-strand 9 hairpin (beta8/9 peptide, amino acids 95-114), which has been involved in receptor binding. A secondary structure prediction of aFGF carried out by several procedures labels the 95-104 sequence as predominantly alpha-helical. A titration of aFGF with 2,2,2-trifluoroethanol (TFE) induces a change in the far-UV CD spectrum of the protein giving rise to a prominent alpha-helical shape (22% alpha-helix). The cooperativity of the transition and the moderate TFE concentrations used (midpoint at 24%) suggest that the effect of TFE is specific. Moreover, a titration performed at pH 2 yields a higher amount of alpha-helix (55%) at a smaller TFE concentration. Synthetic peptides containing the beta8 and beta8/9 sequences display a random coil conformation at pH 7 but acquire alpha-helical structure in the presence of TFE, methanol, and SDS micelles. At pH below 3.0 a significant amount (20-30%) of alpha-helical conformation is present in both the beta8 and beta8/9 peptides even in the absence of other solvent additives. The secondary structure of the peptides was determined by proton nuclear magnetic resonance (1H NMR). These results suggest that the 95-114 sequence of aFGF has helical propensity and that the protein may fold nonhierarchically in the early steps of folding, acquiring its final beta-structure by a later interaction with the rest of the polypeptide.
Sanz
Jesús M
JM
Departamento de Estructura y Función de Proteínas, Centro de Investigaciones Biológicas and Instituto de Quømica-Føsica Rocasolano (CSIC), Madrid, Spain. jmsanz@umh.es
Jiménez
M Angeles
MA
Giménez-Gallego
Guillermo
G
D000595:Amino Acid Sequence; D002942:Circular Dichroism; D016220:Fibroblast Growth Factor 1 / Q000737:chemistry*; D066298:In Vitro Techniques; D009682:Magnetic Resonance Spectroscopy; D000432:Methanol; D008823:Micelles; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013816:Thermodynamics; D014270:Trifluoroethanol / Q000494:pharmacology
D008823:Micelles; D010446:Peptide Fragments; D016220:Fibroblast Growth Factor 1; D014270:Trifluoroethanol; D000432:Methanol