title: Backbone dynamics of the calcium-signaling protein apo-S100B as determined by 15N NMR relaxation.
abstract: Backbone dynamics of homodimeric apo-S100B were studied by (15)N nuclear magnetic resonance relaxation at 9.4 and 14.1 T. Longitudinal relaxation (T(1)), transverse relaxation (T(2)), and the (15)N-[(1)H] NOE were measured for 80 of 91 backbone amide groups. Internal motional parameters were determined from the relaxation data using the model-free formalism while accounting for diffusion anisotropy. Rotational diffusion of the symmetric homodimer has moderate but statistically significant prolate axial anisotropy (D( parallel)/D( perpendicular) = 1.15 +/- 0.02), a global correlation time of tau(m) = 7.80 +/- 0.03 ns, and a unique axis in the plane normal to the molecular symmetry axis. Of 29 residues at the dimer interface (helices 1 and 4), only one has measurable internal motion (Q71), and the order parameters of the remaining 28 were the highest in the protein (S(2) = 0.80 to 0.91). Order parameters in the typical EF hand calcium-binding loop (S(2) = 0.73 to 0.87) were slightly lower than in the pseudo-EF hand (S(2) = 0.75 to 0.89), and effective internal correlation times, tau(e), distinct from global tumbling, were detected in the calcium-binding loops. Helix 3, which undergoes a large, calcium-induced conformational change necessary for target-protein binding, does not show evidence of interchanging between the apo and Ca(2+)-bound orientations in the absence of calcium but has rapid motion in several residues throughout the helix (S(2) = 0.78 to 0.88; 10 < or = tau(e) < or = 30 ps). The lowest order parameters were found in the C-terminal tail (S(2) = 0.62 to 0.83). Large values for chemical exchange also occur in this loop and in regions nearby in space to the highly mobile C-terminal loop, consistent with exchange broadening effects observed.
authors: University of Maryland School of Medicine, Department of Biochemistry and Molecular Biology, Baltimore, Maryland 21201, USA.
authors: K G
authors: KG
authors: Inman
authors: D M
authors: DM
authors: Baldisseri
authors: K E
authors: KE
authors: Miller
authors: D J
authors: DJ
authors: Weber
mesh_terms: D000595:Amino Acid Sequence; D001059:Apoproteins / Q000737:chemistry*; D020013:Calcium Signaling; D002135:Calcium-Binding Proteins / Q000737:chemistry*; D003198:Computer Simulation; D020832:EF Hand Motifs; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009414:Nerve Growth Factors / Q000737:chemistry*; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D011487:Protein Conformation; D064568:S100 Calcium Binding Protein beta Subunit; D009418:S100 Proteins / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D001059:Apoproteins; D002135:Calcium-Binding Proteins; D009414:Nerve Growth Factors; D009587:Nitrogen Isotopes; D064568:S100 Calcium Binding Protein beta Subunit; D009418:S100 Proteins