title: Structural and functional insights into thermally stable cytochrome c' from a thermophile.
abstract: Thermophilic Hydrogenophilus thermoluteolus cytochrome c' (PHCP) exhibits higher thermal stability than a mesophilic counterpart, Allochromatium vinosum cytochrome c' (AVCP), which has a homo-dimeric structure and ligand-binding ability. To understand the thermal stability mechanism and ligand-binding ability of the thermally stable PHCP protein, the crystal structure of PHCP was first determined. It formed a homo-dimeric structure, the main chain root mean square deviation (rmsd) value between PHCP and AVCP being 0.65 Å. In the PHCP structure, six specific residues appeared to strengthen the heme-related and subunit-subunit interactions, which were not conserved in the AVCP structure. PHCP variants having altered subunit-subunit interactions were more severely destabilized than ones having altered heme-related interactions. The PHCP structure further revealed a ligand-binding channel and a penta-coordinated heme, as observed in the AVCP protein. A spectroscopic study clearly showed that some ligands were bound to the PHCP protein. It is concluded that the dimeric PHCP from the thermophile is effectively stabilized through heme-related and subunit-subunit interactions with conservation of the ligand-binding ability.
  
  
  
  We report the X-ray crystal structure of cytochrome c' (PHCP) from thermophilic Hydrogenophilus thermoluteolus. The high thermal stability of PHCP was attributed to heme-related and subunit-subunit interactions, which were confirmed by a mutagenesis study. The ligand-binding ability of PHCP was examined by spectrophotometry. PHCP acquired the thermal stability with conservation of the ligand-binding ability. This study furthers the understanding of the stability and function of cytochromes c.
authors.affiliation: Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan.
authors.forename: Sotaro
authors.initials: S
authors.lastname: Fujii
authors.affiliation: Graduate School of Pharmaceutical Sciences, Osaka University, Yamadaoka, Suita, Osaka, Japan.
authors.forename: Hiroya
authors.initials: H
authors.lastname: Oki
authors.affiliation: Graduate School of Pharmaceutical Sciences, Osaka University, Yamadaoka, Suita, Osaka, Japan.
authors.forename: Kazuki
authors.initials: K
authors.lastname: Kawahara
authors.affiliation: Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Yamane
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology, Ikoma, Nara, Japan.
authors.forename: Masaru
authors.initials: M
authors.lastname: Yamanaka
authors.affiliation: Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Maruno
authors.affiliation: Graduate School of Engineering, Osaka University, Yamadaoka, Suita, Osaka, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kobayashi
authors.affiliation: Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan.
authors.forename: Misa
authors.initials: M
authors.lastname: Masanari
authors.affiliation: Graduate School of Science, Technology, and Innovation, Kobe University, Rokkodai, Kobe, Hyogo, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Wakai
authors.affiliation: Faculty of Agriculture, Ibaraki University, Inashikigun, Ibaraki, Japan.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Nishihara
authors.affiliation: Graduate School of Pharmaceutical Sciences, Osaka University, Yamadaoka, Suita, Osaka, Japan.
authors.forename: Tadayasu
authors.initials: T
authors.lastname: Ohkubo
authors.affiliation: Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Hiroshima, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Sambongi
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D002841:Chromatiaceae / Q000201:enzymology; D018360:Crystallography, X-Ray; D045305:Cytochromes c' / Q000737:chemistry*; D004795:Enzyme Stability; D006358:Hot Temperature; D043363:Hydrogenophilaceae / Q000201:enzymology*; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary
chemical_list: D001426:Bacterial Proteins; D045305:Cytochromes c'
keywords: cytochrome c; ligand-binding; mutagenesis; protein stability; protein structure; thermophile