title: Cytochromes c in Archaea: distribution, maturation, cell architecture, and the special case of Ignicoccus hospitalis.
abstract: Cytochromes c (Cytc) are widespread electron transfer proteins and important enzymes in the global nitrogen and sulfur cycles. The distribution of Cytc in more than 300 archaeal proteomes deduced from sequence was analyzed with computational methods including pattern and similarity searches, secondary and tertiary structure prediction. Two hundred and fifty-eight predicted Cytc (with single, double, or multiple heme c attachment sites) were found in some but not all species of the Desulfurococcales, Thermoproteales, Archaeoglobales, Methanosarcinales, Halobacteriales, and in two single-cell genome sequences of the Thermoplasmatales, all of them Cren- or Euryarchaeota. Other archaeal phyla including the Thaumarchaeota are so far free of these proteins. The archaeal Cytc sequences were bundled into 54 clusters of mutual similarity, some of which were specific for Archaea while others had homologs in the Bacteria. The cytochrome c maturation system I (CCM) was the only one found. The highest number and variability of Cytc were present in those species with known or predicted metal oxidation and/or reduction capabilities. Paradoxical findings were made in the haloarchaea: several Cytc had been purified biochemically but corresponding proteins were not found in the proteomes. The results are discussed with emphasis on cell morphologies and envelopes and especially for double-membraned Archaea-like Ignicoccus hospitalis. A comparison is made with compartmentalized bacteria such as the Planctomycetes of the Anammox group with a focus on the putative localization and roles of the Cytc and other electron transport proteins.
authors.affiliation: Department of Biology, Sulfur Biochemistry and Microbial Bioenergetics, Technische Universität Darmstadt Darmstadt, Germany.
authors.forename: Arnulf
authors.initials: A
authors.lastname: Kletzin
authors.affiliation: Fakultät für Biologie und Vorklinische Medizin, Zentrum für Elektronenmikroskopie, Universität Regensburg Regensburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Heimerl
authors.affiliation: Fakultät für Biologie und Vorklinische Medizin, Zentrum für Elektronenmikroskopie, Universität Regensburg Regensburg, Germany.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Flechsler
authors.affiliation: Department of Microbiology, Institute for Water and Wetland Research, Radboud University Nijmegen Nijmegen, Netherlands.
authors.forename: Laura
authors.initials: L
authors.lastname: van Niftrik
authors.affiliation: Fakultät für Biologie und Vorklinische Medizin, Zentrum für Elektronenmikroskopie, Universität Regensburg Regensburg, Germany.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Rachel
authors.affiliation: Department of Biology I, Plant Development, Biocenter LMU Munich Planegg-Martinsried, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Klingl
keywords: ANME; Archaea; Ignicoccus hospitalis; anammox planctomycetes; bioinformatics; cytochrome c; molecular modeling