title: Structural analysis of zinc-substituted cytochrome c.
abstract: Zinc-substituted cytochrome c has been widely used in studies of protein-protein interactions and photo-induced electron transfer reactions between proteins. However, the coordination geometry of zinc in zinc-substituted cyt c has not yet been determined; two different opinions about the coordination have been reached. Here the solution structures of zinc-substituted cytochrome c that might be five-coordinated and six-coordinated have been refined separately by using (1)H NMR spectroscopy, and the zinc coordination geometry was determined just by NOE distance constraints. Structural analysis of the energy-minimized average solution structures of both the pentacoordinated and hexacoordinated geometries indicate that that zinc in zinc-substituted cyt c should be bound to both His18 and Met80, which means that the zinc is six-coordinated. RMSD values of the family of 25 six-coordinated structures from the average structure are 0.66+/-0.13 A and 1.09+/-0.16 A for the backbone and all heavy atoms, respectively. A statistical analysis of the structure indicates its satisfactory quality. Comparison of the solution structure of the six-coordinated energy-minimized average structure of zinc-substituted cytochrome c with the solution structure of reduced cytochrome c reveals that for the overall folding the secondary structure elements are very close. The availability of the structure provides for a better understanding of the protein-protein complex and for electron transfer processes between Zn cyt c and other metalloproteins.
authors.affiliation: State Key Laboratory of Coordination Chemistry, Nanjing University, 210093, Nanjing, PR China.
authors.forename: Chengmin
authors.initials: C
authors.lastname: Qian
authors.forename: Yong
authors.initials: Y
authors.lastname: Yao
authors.forename: Yufeng
authors.initials: Y
authors.lastname: Tong
authors.forename: Jinfeng
authors.initials: J
authors.lastname: Wang
authors.forename: Wenxia
authors.initials: W
authors.lastname: Tang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D045304:Cytochromes c / Q000737:chemistry*; D006736:Horses; D008969:Molecular Sequence Data; D015394:Molecular Structure; D015032:Zinc / Q000737:chemistry*
chemical_list: D045304:Cytochromes c; D015032:Zinc