Crystal structure of cytochrome c' from Rhodocyclus gelatinosus and comparison with other cytochromes c'

Margarida Archer, Lucia Banci, Elena Dikaya, Maria J. Romão

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18 Citations (Scopus)

Abstract

Cytochromes c' are heme proteins found in photosynthetic and denitrifying bacteria, where they are presumably involved in electron transport. The cytochrome c' isolated from the bacterium Rhodocyclus gelatinosus (RGCP) forms a homodimer with each polypeptide containing 129 residues. It has been crystallised in ammonium sulfate at pH 6. Crystals belong to space group P3121 with cell parameters a = 70.2 Å and c = 126.8 Å, which corresponds to a dimer in the asymmetric unit (VM = 3.5 Å3/Da). The crystal structure of RGCP was solved by the molecular replacement method and refined using data to 2.5-Å resolution. The final crystallographic R factor was 17.9% for all reflections (above 2 σ) in the resolution range 27.4 to 2.5 Å. The refined model includes 1876 non-hydrogen protein atoms and 56 water molecules. As typical of c-type cytochromes, the heme group is covalently bound to Cys-X-Y-Cys-His through thio-ether bonds, and His123 occupies the fifth axial coordination position. On the vacant 'distal' site; Phe16 blocks the direct access to the sixth coordination site, which is in a predominantly hydrophobic environment. In spite of the low sequence homology among cytochromes c' the overall fold is similar. The monomer structure consists of 4 anti-parallel α-helices and has random coils in the loops between the helices, and at the N- and C-termini. The subunits cross each other to form an X shape.

Original languageEnglish
Pages (from-to)611-622
Number of pages12
JournalJournal of Biological Inorganic Chemistry
Volume2
Issue number5
DOIs
Publication statusPublished - 1 Oct 1997

Keywords

  • Cytochrome c'
  • Electron transfer protein
  • Rhodocyclus gelatinosus
  • X-ray crystal structure

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