1fj0
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STRUCTURE DETERMINATION OF THE FERRICYTOCHROME C2 FROM RHODOPSEUDOMONAS PALUSTRIS
OverviewOverview
The three-dimensional structures of the native cytochrome c(2) from, Rhodopseudomonas palustris and of its ammonia complex have been obtained, at pH 4.4 and pH 8.5, respectively. The structure of the native form has, been refined in the oxidized state at 1.70 A and in the reduced state at, 1.95 A resolution. These are the first high-resolution crystal structures, in both oxidation states of a cytochrome c(2) with relatively high redox, potential (+350 mV). The differences between the two oxidation states of, the native form, including the position of internal water molecules, are, small. The unusual six-residue insertion Gly82-Ala87, which precedes the, heme binding Met93, forms an isolated 3(10)-helix secondary structural, element not previously observed in other c-type cytochromes. Furthermore, this cytochrome shows an external methionine residue involved in a, strained folding near the exposed edge of the heme. The structural, comparison of the present cytochrome c(2) with other c-type cytochromes, has revealed that the presence of such a residue, with torsion angles phi, and psi of approximately -140 and -130 degrees, respectively, is a typical, feature of this family of proteins. The refined crystal structure of the, ammonia complex, obtained at 1.15 A resolution, shows that the sulphur, atom of the Met93 axial ligand does not coordinate the heme iron atom, but, is replaced by an exogenous ammonia molecule. This is the only example so, far reported of an X-ray structure with the heme iron coordinated by an, ammonia molecule. The detachment of Met93 is accompanied by a very, localized change in backbone conformation, involving mainly the residues, Lys92, Met93, and Thr94. Previous studies under typical denaturing, conditions, including high-pH values and the presence of exogenous, ligands, have shown that the detachment of the Met axial ligand is a basic, step in the folding/unfolding process of c-type cytochromes. The ammonia, adduct represents a structural model for this important step of the, unfolding pathway. Factors proposed to be important for the methionine, dissociation are the strength of the H-bond between the Met93 and Tyr66, residues that stabilizes the native form, and the presence in this, bacterial cytochrome c(2) of the rare six-residue insertion in the helix, 3(10) conformation that increases Met loop flexibility.
About this StructureAbout this Structure
1FJ0 is a Single protein structure of sequence from Rhodopseudomonas palustris with SO4, HEM and GOL as ligands. Full crystallographic information is available from OCA.
ReferenceReference
Cleavage of the iron-methionine bond in c-type cytochromes: crystal structure of oxidized and reduced cytochrome c(2) from Rhodopseudomonas palustris and its ammonia complex., Geremia S, Garau G, Vaccari L, Sgarra R, Viezzoli MS, Calligaris M, Randaccio L, Protein Sci. 2002 Jan;11(1):6-17. PMID:11742117
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