Cytochromes

The heme group, Fe-protoporphyrin IX, is one of nature's most widely used metal cofactors. Its roles are in transport of small molecules, electron transfer and catalysis. Different classes of heme proteins containing variants of the original heme group are known today, and among these our focus is on the cytochrome c family. Here, the cofactor is covalently linked to the protein chain via thioether bonds to the cysteine residues of a conserved binding motif, and this has a series of important structural and functional consequences. For once, the cofactor cannot easily be lost, so that c-type cytochromes are ideal extracellular proteins, or are located in 'extracytoplasmic' compartments such as the periplasm of Gram-negative bacteria or the intermembrane space of mitochondria or chloroplasts. Second, the attachment of heme groups to the peptide chains occurs before the protein folds, allowing for a very high heme:protein ratio. This gives rise to cytochrome with many hemes attached to a rather short peptide: multiheme cytochromes c.

Multiheme cytochromes c act as electron carriers or as redox enzymes that can catalze multi-electron transfer reactions.  

References:

• Einsle, O. (2012) Enzyme or Electrode?  Structure, 20, 1132-1134.
• Seidel, J., Hoffmann, M., Ellis, K.E., Seidel, A., Spatzal, T., Gerhardt, S., Elliott, S.J. & Einsle, O. (2012) MacA is a second cytochrome c Peroxidase in Geobacter sulfurreducens.  Biochemistry, 51, 2747-2456.
• Simon, J., Kern, M., Hermann, B., Einsle, O. & Butt, J.N. (2011) Physiological function and catalytic versatility of bacterial multihaem cytochromes c involved in nitrogen and sulfur cycling.  Biochem. Soc. Transact., 39, 1864-1870.
• Schütz, B., Seidel, J., Sturm, G., Einsle, O. & Gescher, J. (2011) Investigation of the electron transport chain to and the catalytic activity of the diheme cytochrome c peroxidase CcpA of Shewanella oneidensis. Appl. Environ. Microbiol., 77, 6172-6180.
• Ellis, K.E., Seidel, J., Einsle, O. & Elliott, S.J. (2011) Geobacter sulfurreducens cytochrome c peroxidases: Eletrochemical classifications of catalytic mechanisms. Biochemistry, 50, 4513-4520.
• Einsle, O. (2011) Structure and function of formate-dependent cytochrome c nitrite reductase.  Meth. Enzymol., 496, 399-422.
• Hoffmann, M., Seidel, J. & Einsle, O. (2009) CcpA from Geobacter sulfurreducens is a Basic Di-heme Cytochrome c Peroxidase., J. Mol. Biol., 393, 951-965. 
• Heitmann, D. & Einsle, O. (2008) Pseudo-merohedral twinning in crystals of the diheme c-type cytochrome DHC2 from Geobacter sulfurreducens.  Acta Crystallogr., D64, 993-999.
• Lukat, P., Hoffmann, M. & Einsle, O. (2008) Crystal packing of the c₆-type cytochrome OmcF from Geobacter sulfurreducens is mediated by an N-terminal Strep-tag II. 
Acta Crystallogr., D64, 919-926.
• Kern, M., Einsle, O. & Simon, J. (2008) Variants of the tetrahaem cytochrome c quinol dehydrogenase NrfH characterize the menaquinol binding site, the haem c binding motifs and the transmembrane segment.
 Biochem. J., 414, 73-79.
• Hoffmann, M., Braaz, R., Jendrossek, D. & Einsle, O. (2008) Crystallization of the extracellular rubber oxygenase RoxA from Xanthomonas sp. Strain 35Y. 
Acta Crystallogr., F64, 123-125.
• Lukat, P., Rudolf, M., Stach, P., Messerschmidt, A., Kroneck, P. M. H., Simon, J. & Einsle, O. (2008) Binding and Reduction of Sulfite by Cytochrome c Nitrite Reductase. 
Biochemistry, 47, 2080-2086.
• Heitmann, D. & Einsle, O. (2005) Structural and Biochemical Characterization of DHC2, a Novel Diheme Cytochrome c from Geobacter sulfurreducens.
Biochemistry, 44, 12411-12419.
• Einsle, O., Messerschmidt, A., Huber, R., Kroneck, P. M. H. & Neese, F. (2002) Mechanism of the six-electron reduction of nitrite to ammonia by cytochrome c nitrite reductase. 
J. Am. Chem. Soc., 124, 11737-11745.
• Rudolf, M., Einsle, O., Neese, F. & Kroneck, P. M. H. (2002) Pentahaem cytochrome c nitrite reductase: reaction with hydroxylamine, a potential reaction intermediate and substrate. 
Biochem. Soc. Transact., 30, 649-653.
• Einsle, O., Stach, P., Messerschmidt, A., Klimmek, O., Simon, J., Kröger, A. & Kroneck, P. M. H. (2002) Crystallization and preliminary X-ray analysis of the membrane-bound cytochrome c nitrite reductase complex (NrfHA) fromWolinella succinogenes. 
Acta Crystallogr., D58, 341-342.
• Einsle, O. (2001) Cytochrome c nitrite reductase.  In: Handbook of Metalloproteins(Messerschmidt, A., Huber, R., Wieghardt, K. & Poulos, T., eds.). John Wiley & Sons, NewYork.
• Einsle, O., Foerster, S., Mann, K. H., Fritz, G., Messerschmidt, A. & Kroneck, P. M. H. (2001) Spectroscopic investigation, reactivity and structure determination of the tetraheme cytochrome c₃ from Desulfovibrio desulfuricans Essex 6. 
Eur. J. Biochem., 268, 3028-3035.
• Simon, J., Gross, R., Einsle, O., Kroneck, P. M. H., Kröger, A. & Klimmek, O.(2000) A NapC/NirT-type cytochrome c (NrfH) is the mediator between the quinone pool and the cytochrome c nitrite reductase of Wolinella succinogenes. 
Mol. Microbiol., 35, 686-696.
• Einsle, O., Stach, P., Messerschmidt, A., Simon, J., Kröger, A., Huber, R. & Kroneck, P. M. H. (2000) Cytochrome c nitrite reductase from Wolinella succinogenes: Structure at 1.6 Å resolution, inhibitor binding and heme-packing motifs. 
J. Biol. Chem., 275, 39608-39616.
• Stach, P., Einsle, O., Schumacher, W., Kurun, E. & Kroneck, P. M. H. (2000) Bacterial cytochrome c nitrite reductase: new structural and functional aspects. 
J. Inorg. Biochem., 79, 381-385.
• Einsle, O., Messerschmidt, A., Stach, P., Bourenkov, G. P., Bartunik, H. D., Huber, R. & Kroneck, P. M. H. (1999) Structure of cytochrome c nitrite reductase. Nature, 400, 476-480.
• Einsle, O., Schumacher, W., Kurun, E., Nath, U. & Kroneck, P. M. H. (1998) Cytochrome c nitrite reductase from Sulfurospirillum deleyianum andWolinella succinogenes. Molecular and spectroscopic properties of the multihaem enzyme. 
In: Biological Electron Transfer Chains: Genetics, Composition and Mode of Operation (Canters, G. W. & Vijgenboom, E., eds.), pp. 197-208. Kluwer Academic Press.