AUTHOR=Kletzin Arnulf , Heimerl Thomas , Flechsler Jennifer , van Niftrik Laura , Rachel Reinhard , Klingl Andreas 

TITLE=Cytochromes c in Archaea: distribution, maturation, cell architecture, and the special case of Ignicoccus hospitalis

JOURNAL=Frontiers in Microbiology

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2015.00439

DOI=10.3389/fmicb.2015.00439

ISSN=1664-302X

ABSTRACT=<p>Cytochromes <italic>c</italic> (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 <italic>c</italic> attachment sites) were found in some but not all species of the <italic>Desulfurococcales, Thermoproteales, Archaeoglobales, Methanosarcinales, Halobacteriales</italic>, and in two single-cell genome sequences of the <italic>Thermoplasmatales</italic>, all of them <italic>Cren</italic>- or <italic>Euryarchaeota</italic>. Other archaeal phyla including the <italic>Thaumarchaeota</italic> 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 <italic>c</italic> 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 <italic>Ignicoccus hospitalis</italic>. A comparison is made with compartmentalized bacteria such as the <italic>Planctomycetes</italic> of the Anammox group with a focus on the putative localization and roles of the Cytc and other electron transport proteins.</p>