title: Crystal structure of Azotobacter cytochrome c5 at 2.5 A resolution.
abstract: The crystal structure of cytochrome c5 from Azotobacter vinelandii has been solved and refined to an R value of 0.29 at 2.5 A resolution. The structure of the oxidized protein was solved using a monoclinic crystal form. The structure was solved by multiple isomorphous replacements, re-fit to a solvent-leveled multiple isomorphous replacement map, and refined by restrained least squares. The structure reveals monomers associated about the crystallographic 2-fold axis by hydrophobic contacts at the "exposed heme edge". The overall conformation for the monomer is similar to that of Pseudomonas aeruginosa cytochrome c551. However, relative to a common heme conformation, c5 and c551 differ by an average of 6.8 A over 82 alpha-carbon positions and the propionates of c5 are much more exposed to solvent. The shortest heme--heme contact at the "dimer" interface is 6.3 A (Fe to Fe 16.4 A). Alignment of c5 and c551 shows that the two cytochromes, in spite of sequence differences, have remarkably similar charge distributions. A disulfide stacks on a tyrosine between the N- and C-terminal helices.
authors.forename: D C
authors.initials: DC
authors.lastname: Carter
authors.forename: K A
authors.initials: KA
authors.lastname: Melis
authors.forename: S E
authors.initials: SE
authors.lastname: O'Donnell
authors.forename: B K
authors.initials: BK
authors.lastname: Burgess
authors.forename: W R
authors.initials: WR
authors.lastname: Furey
authors.forename: B C
authors.initials: BC
authors.lastname: Wang
authors.forename: C D
authors.initials: CD
authors.lastname: Stout
mesh_terms: D000595:Amino Acid Sequence; D001395:Azotobacter / Q000032:analysis*; D003461:Crystallography; D003574:Cytochrome c Group; D011549:Pseudomonas / Q000032:analysis; D011550:Pseudomonas aeruginosa / Q000032:analysis
chemical_list: D003574:Cytochrome c Group; C046450:cytochrome C5