title: Hyperstability and crystal structure of cytochrome c(555) from hyperthermophilic Aquifex aeolicus.
abstract: In order to elucidate the relationship between the stability and the structure of the monohaem cytochrome c(555) (AA c(555)) from the hyperthermophilic bacterium Aquifex aeolicus, chemical denaturation and crystal structure determination were carried out. AA c(555) exhibited higher stability than the thermophilic Hydrogenobacter thermophilus cytochrome c(552) (HT c(552)), which is one of the most stable cytochromes c. The three-dimensional crystal structure of AA c(555), which was determined using the multiple anomalous dispersion technique at 1.15 A resolution, included a unique 14-residue extra helix, while the side-chain interactions of several amino-acid residues responsible for the stability of HT c(552) were conserved in AA c(555). The side chain of the Met61 residue in the extra helix was aligned towards the haem, forming a coordination bond between the Met S and haem Fe atoms. In other cytochromes c the corresponding regions always form Omega loops which also include the haem-liganding Met residue and are known to be involved in the initial step in cytochrome c denaturation. The formation of the extra helix in AA c(555) results in the highest helix content, 59.8%, among the monohaem cytochromes c. The extra helix should mainly contribute to the hyperstability of AA c(555) and is presumed to be a novel strategy of cytochromes c for adaptation to a hyperthermophilic environment.
authors.affiliation: Hiroshima University, Japan.
authors.forename: Marii
authors.initials: M
authors.lastname: Obuchi
authors.forename: Kazuki
authors.initials: K
authors.lastname: Kawahara
authors.forename: Daisuke
authors.initials: D
authors.lastname: Motooka
authors.forename: Shota
authors.initials: S
authors.lastname: Nakamura
authors.forename: Masaru
authors.initials: M
authors.lastname: Yamanaka
authors.forename: Taku
authors.initials: T
authors.lastname: Takeda
authors.forename: Susumu
authors.initials: S
authors.lastname: Uchiyama
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Tadayasu
authors.initials: T
authors.lastname: Ohkubo
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Sambongi
mesh_terms: D000220:Adaptation, Biological; D001419:Bacteria / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D003460:Crystallization; D018360:Crystallography, X-Ray; D003574:Cytochrome c Group / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D045222:Electron Transport Chain Complex Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D006358:Hot Temperature; D007502:Iron Chelating Agents / Q000737:chemistry / Q000378:metabolism; D008715:Methionine / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D055550:Protein Stability
chemical_list: D001426:Bacterial Proteins; D003574:Cytochrome c Group; D045222:Electron Transport Chain Complex Proteins; D007502:Iron Chelating Agents; C022302:cytochrome C-552; D008715:Methionine