title: NMR study of the conformational transition of cytochrome c upon the displacement of Met80 by exogenous ligand: structural and magnetic characterization of azidoferricytochrome c.
abstract: As the exogenous ligand-cytochrome c complexes were purported to represent models for the unfolding intermediate of cytochrome c, NMR spectroscopy has been utilized to study the azide adduct of horse heart cytochrome c. The structure of azidoferricytochrome c was modeled by restrained energy minimization using paramagenetic pseudocontact shifts as constraints. The bound azide moiety was found to be tilted approximately 15 degrees from the heme normal. The displacement of Met80 by the exogenous azide molecule causes large structural rearrangement in the distal cavity. Furthermore, the conformation transition associated with the swing out of the loop containing Met80 and the shift of the 50s-helix increases the solvent accessibility of the heme group. To elucidate the heme electronic structure of the complex, the paramagnetic 13C shifts were analyzed in terms of a model based on the pi molecular orbitals of the heme under perturbed D(4) symmetry. It turned out that the His-Fe bonding provides the protein constraint that orients the in-plane anisotropy in the complex. The electronic properties are in accordance with the calculated magnetic susceptibility anisotropy and the structural information.
authors.affiliation: State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, PR China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Yao
authors.forename: Yibing
authors.initials: Y
authors.lastname: Wu
authors.forename: Chengmin
authors.initials: C
authors.lastname: Qian
authors.forename: Keqong
authors.initials: K
authors.lastname: Ye
authors.forename: Jinfeng
authors.initials: J
authors.lastname: Wang
authors.forename: Wenxia
authors.initials: W
authors.lastname: Tang
mesh_terms: D000818:Animals; D001386:Azides / Q000737:chemistry*; D003574:Cytochrome c Group / Q000737:chemistry* / Q000378:metabolism; D006418:Heme / Q000737:chemistry; D006736:Horses; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008715:Methionine / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D009206:Myocardium / Q000378:metabolism; D017510:Protein Folding; D017433:Protein Structure, Secondary
chemical_list: D001386:Azides; D003574:Cytochrome c Group; D008024:Ligands; D006418:Heme; D008715:Methionine