title: Amplitudes and directions of internal protein motions from a JAM analysis of 15N relaxation data.
abstract: A method has been developed for characterizing dynamic structures of proteins in solution by using nuclear magnetic resonance (NMR) restraints and 15N relaxation data. This method is based on the concept of the jumping-among-minima (JAM) model. In this model we assume that protein dynamics can be described on the basis of conformational substates, and involves intra- and inter-substate motion. A set of substates is created by picking energy-minimized conformations from the conformational space consistent with the geometric NMR restraints. Intra-substate motions, which occur on the timescale of approximately 10 ps, are simulated with molecular dynamics (MD) calculations with force-field energy terms. Statistical weights of the conformational substates are determined to reproduce the NMR relaxation parameters. The refinement procedure consists of four stages: (i) determination of the ensemble of structures that satisfy NMR restraints, (ii) determination of intra-substate fluctuation, (iii) determination of statistical weights of conformational substates to reproduce model-free relaxation parameters, and (iv) analysis of the resulting dynamic structure to determine amplitudes and directions of internal protein motions. This method was employed to investigate structure and dynamics of the adhesion domain of human CD2 (hCD2) in solution. Two major collective modes, whose contributions to atomic mean-square fluctuations are 77.1% in total, are identified by the refinement. The first mode is interpreted as a rigid-body motion of a protein segment consisting of a part of the B--C loop, a part of the F strand, and the F--G loop. Another type of smaller-amplitude mode is indicated for the C'--C'' loop. The motions affect primarily the curvature of the slightly concave counterreceptor-binding site and represent transitions between a concave (closed) and flat (open) binding face. By comparing the ensemble of structures in solution to the complex structure with counterreceptor CD58, we found that these two types of motions resemble the change upon counterreceptor binding.
authors.affiliation: Institute of Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113-0032, Japan.
authors.forename: Akio
authors.initials: A
authors.lastname: Kitao
authors.forename: Gerhard
authors.initials: G
authors.lastname: Wagner
mesh_terms: D008958:Models, Molecular; D009587:Nitrogen Isotopes / Q000032:analysis; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry
chemical_list: D009587:Nitrogen Isotopes; D011506:Proteins; D012996:Solutions