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Published online before print May 7, 2004, 10.1110/ps.04626204
Protein Science (2004), 13:1684-1692. Published by Cold Spring Harbor Laboratory Press. Copyright © 2004 The Protein Society
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FOR THE RECORD

Structure of a novel c7-type three-heme cytochrome domain from a multidomain cytochrome c polymer

P. Raj Pokkuluri1,4, Yuri Y. Londer1,4, Norma E.C. Duke1, Jill Erickson1, Miguel Pessanha2, Carlos A. Salgueiro2,3 and Marianne Schiffer1

1 Biosciences Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
2 Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Rua da Quinta Grande 6, 2780-156 Oeiras, Portugal
3 Departamento de Química da Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa, Quinta da Torre, 2825-114 Caparica, Portugal

(RECEIVED January 12, 2004; FINAL REVISION February 27, 2004; ACCEPTED March 1, 2004)



Abstract

The structure of a novel c7-type cytochrome domain that has two bishistidine coordinated hemes and one heme with histidine, methionine coordination (where the sixth ligand is a methionine residue) was determined at 1.7 Å resolution. This domain is a representative of domains that form three polymers encoded by the Geobacter sulfurreducens genome. Two of these polymers consist of four and one protein of nine c7-type domains with a total of 12 and 27 hemes, respectively. Four individual domains (termed A, B, C, and D) from one such multiheme cytochrome c (ORF03300 were cloned and expressed in Escherichia coli. The domain C produced diffraction quality crystals from 2.4 M sodium malonate (pH 7). The structure was solved by MAD method and refined to an R-factor of 19.5% and R-free of 21.8%. Unlike the two c7 molecules with known structures, one from G. sulfurreducens (PpcA) and one from Desulfuromonas acetoxidans where all three hemes are bishistidine coordinated, this domain contains a heme which is coordinated by a methionine and a histidine residue. As a result, the corresponding heme could have a higher potential than the other two hemes. The apparent midpoint reduction potential, Eapp, of domain C is –105 mV, 50 mV higher than that of PpcA.

Keywords: multiheme cytochrome c; cytochrome c7; Geobacter metallireducens; Geobacter sulfurreducens; heme coordination in c-type cytochromes; protein structure

Abbreviations: Eapp, apparent midpoint reduction potential • MAD, multiple wavelength anamolous dispersion • PDB, Protein Data Bank

Reprint requests to: Marianne Schiffer, Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA; e-mail: mschiffer{at}anl.gov; fax: (630) 252-3387.

4 These authors contributed equally to this work.

Article published online ahead of print. Article and publication are at http://www.proteinscience.org/cgi/doi/10.1110/ps.04626204.


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