title: Study of conformational rearrangement and refinement of structural homology models by the use of heteronuclear dipolar couplings.
abstract: For an increasing fraction of proteins whose structures are being studied, sequence homology to known structures permits building of low resolution structural models. It is demonstrated that dipolar couplings, measured in a liquid crystalline medium, not only can validate such structural models, but also refine them. Here, experimental 1H-15N, 1Halpha-13Calpha, and 13C'-13Calpha dipolar couplings are shown to decrease the backbone rmsd between various homology models of calmodulin (CaM) and its crystal structure. Starting from a model of the Ca2+-saturated C-terminal domain of CaM, built from the structure of Ca2+-free recoverin on the basis of remote sequence homology, dipolar couplings are used to decrease the rmsd between the model and the crystal structure from 5.0 to 1.25 A. A better starting model, built from the crystal structure of Ca2+-saturated parvalbumin, decreases in rmsd from 1.25 to 0.93 A. Similarly, starting from the structure of the Ca2+-ligated CaM N-terminal domain, experimental dipolar couplings measured for the Ca2+-free form decrease the backbone rmsd relative to the refined solution structure of apo-CaM from 4.2 to 1.0 A.
authors.affiliation: Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Chou
authors.forename: S
authors.initials: S
authors.lastname: Li
authors.forename: A
authors.initials: A
authors.lastname: Bax
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism; D005136:Eye Proteins; D005782:Gels; D051597:Hippocalcin; D006801:Humans; D008074:Lipoproteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D010320:Parvalbumins / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary / Q000187:drug effects; D051603:Recoverin; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; D005136:Eye Proteins; D005782:Gels; D008074:Lipoproteins; D009419:Nerve Tissue Proteins; D010320:Parvalbumins; C496731:RCVRN protein, human; D051603:Recoverin; D051597:Hippocalcin; D002118:Calcium