Structure of ferricytochrome c′ from Rhodospirillum molischianum at 1.67 Å resolution

B. C. Finzel, P. C. Weber, K. D. Hardman, F. R. Salemme

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The structure of ferricytochrome c′ from Rhodospirillum molischianum has been crystallographically refined to 1.67 Å resolution using a combination of reciprocal space and restrained least-squares refinement methods. The final crystallographic R-factor for 30,533 reflections measured with I > σ(I) between infinity and 1.67 Å is 0.188. The final model incorporates 1944 unique protein atoms (of a total of 1972) together with 194 bound solvent molecules. The structure has been analysed with respect to its detailed conformational properties, secondary structural features, temperature factor behavior, bound solvent sites, and heme geometry. The asymmetric unit of the cytochrome c′ crystal contains a dimer composed of chemically identical 128-residue polypeptide chains. Although the refined structure shows the monomers to be very similar, examination of the differences that do occur allows an evaluation of how different lattice contacts affect protein conformation and solvent binding. In particular, comparison of solvent binding sites in the two subunits allows identification of a common set that are not altered by lattice interactions. The preservation of these solvent interactions in different lattice environments suggests that they play a structural role in protein stabilization in solution. The refined structure additionally reveals some new features that relate to the ligand binding properties and unusual mixed-spin state character of cytochrome c′. Finally, comparison of the heme binding geometry in cytochrome c′ and other structurally unrelated c-type cytochromes shows that two alternative, but sterically favorable, conformational variants occur among the seven examples examined.

Original languageEnglish (US)
Pages (from-to)627-643
Number of pages17
JournalJournal of Molecular Biology
Issue number3
StatePublished - Dec 5 1985

Bibliographical note

Funding Information:
The authors acknowledge the aid of Dr Robert (1. Ladner for development of interactive computer graphics software. Earlier steps of refinement were done at the IBM Thomas J. Watson Research Center. Yorktown Hts.. NY. This work was supported in part by K.I.H. research grants GM30393 and GM33325.


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