title: 15N NMR relaxation studies of free and ligand-bound human acidic fibroblast growth factor.
abstract: 15N NMR relaxation data have been used to characterize the backbone dynamics of the human acidic fibroblast growth factor (hFGF-1) in its free and sucrose octasulfate (SOS)-bound states. (15)N longitudinal (R(1)), transverse (R(2)) relaxation rates and (1H)-(15)N steady-state nuclear Overhauser effects were obtained at 500 and 600 MHz (at 25 degrees C) for all resolved backbone amide groups using (1)H- detected two-dimensional NMR experiments. Relaxation data were fit to the extended model free dynamics for each NH group. The overall correlation time (tau(m)) for the free and SOS-bound forms were estimated to be 10.4 +/- 1.07 and 11.1 +/- 1.35 ns, respectively. Titration experiments with SOS reveals that the ligand binds specifically to the C-terminal domain of the protein in a 1:1 ratio. Binding of SOS to hFGF-1 is found to induce a subtle conformational change in the protein. Significant conformational exchange (R(ex)) is observed for several residues in the free form of the protein. However, in the SOS-bound form only three residues exhibit significant R(ex) values, suggesting that the dynamics on the micro- to millisecond time scale in the free form is coupled to the cis-trans-proline isomerization. hFGF-1 is a rigid molecule with an average generalized parameter (S(2)) value of 0.89 +/- 0.03. Upon binding to SOS, there is a marked decrease in the overall flexibility (S(2) = 0.94 +/- 0.02) of the hFGF-1 molecule. However, the segment comprising residues 103-111 shows increased flexibility in the presence of SOS. Significant correlation is found between residues that show high flexibility and the putative receptor binding sites on the protein.
authors.affiliation: Department of Chemistry, National Tsing Hua University, Hsinchu 30043, Taiwan.
authors.forename: Y
authors.initials: Y
authors.lastname: Chi
authors.forename: T K
authors.initials: TK
authors.lastname: Kumar
authors.forename: I M
authors.initials: IM
authors.lastname: Chiu
authors.forename: C
authors.initials: C
authors.lastname: Yu
mesh_terms: D001665:Binding Sites; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D016220:Fibroblast Growth Factor 1 / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D007536:Isomerism; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary
chemical_list: D008024:Ligands; D016220:Fibroblast Growth Factor 1