Structural composition of alternative complex III: Variations on the same theme

Abstract

Alternative complex III forms a recently identified family of enzymes with quinol:electron acceptor oxidoreductase activity. First biochemical and genomic analyses showed that ACIII is composed of six to eight subunits, most of which homologous to different proteins or domains already observed in other known enzymatic complexes. The increasing number of completely sequenced genomes led us to perform a new search for the genes coding for the different ACIII subunits. We have identified a larger number of gene clusters coding for ACIII, still confined to the bacterial domain, but extended to classes in which it was not observed before. We also found an unanticipated diversity in gene clusters, both in terms of its constitution and organization. The several unexpected gene arrangements brought new perspectives to the role of the different subunits of ACIII, namely in quinone binding and in proton translocation. This article is part of a Special Issue entitled: Respiratory complex III and related bc complexes.

New Insight into Microbial Iron Oxidation as Revealed by the Proteomic Profile of an Obligate Iron-Oxidizing Chemolithoautotroph

“…A molybdopterin oxidoreductase associated with alternative complex III (ACIII) was identified in PV-1 through preliminary proteomic work (3) and was denoted a "Mob" (Mo-binding) complex, a complex seen in other mi- croaerophilic, neutrophilic FeOB such as Gallionella capsiferriformans, Sideroxydans lithotrophicus (4), and Leptothrix ochracea. In this report, the mob cluster of genes is formally renamed act to be consistent with other reports on ACIII genes in other organisms (34). The act cluster of genes is located upstream of the genes that encode the putative bc 1 complex and includes seven genes: actAB1B2CDEF (see Fig.…”

“…Following the recent discovery of ACIII, there are questions regarding its function even though there have been important advancements from the model organisms Chloroflexus aurantiacus, a filamentous, anoxygenic phototroph, and Rhodothermus marinus, a marine heterotroph (34)(35)(36). The actB genes in these microorganisms encode a large protein that contains domains with homology to a molybdopterin-guanine dinucleotide-containing catalytic subunit in the complex of iron-sulfur molybdoenzyme (CISM) family (domain 1) and to an iron-sulfur protein in the CISM family (domain 2).…”

“…However, peptides for this bc 1 complex are present at relatively low levels in this proteomic profile. Alternatively, it is hypothesized that this function could potentially be performed by ACIII, which has been shown to be an analog of the bc 1 complex (34)(35)(36) and is represented in the profile by a large number of peptides. A recent report (61) presents a remarkably similar model, including reverse electron transport via ACIII, in an uncultivated nonphotosynthetic member of the Chromatiaceae that is capable of growing on biocathodes.…”

Membrane-bound oxygen reductases of the anaerobic sulfate-reducing Desulfovibrio vulgaris Hildenborough: roles in oxygen defence and electron link with periplasmic hydrogen oxidation

“…c 553 remains uncertain. One possibility could be that the MFIc complex (corresponding to the Qrc complex, genes DVU0692-DVU0695 in DvH) described in Rhodothermus marinus or Chloroflexus auriantiacus (Pereira et al, 2007;Yanyushin et al, 2005) serves as an alternative bc 1 complex (Gao et al, 2010;Refojo et al, 2010Refojo et al, , 2013. However, analysis of both Dqrc and DqrcDbd deletion strains argues against the involvement of the Qrc complex as an alternative bc 1 complex (unpublished data), in line with the reverse menaquinone reductase activity reported (Venceslau et al, 2010 (Venceslau et al, 2010), the HmC complex (Dolla et al, 2000) or another as-yetunidentified cyt.…”

Draft Genome of Thermanaerothrix daxensis GNS-1, a Thermophilic Facultative Anaerobe from the Chloroflexi Class Anaerolineae

“…It encodes for Complex I (NADH dehydrogenase), Complex II (succinate dehydrogenase), and an aerobic CO dehydrogenase. It also has two aerobic respiration modules; an A-family heme-copper oxygen reductase coupled to an alternative complex III (ACIII) ( 5 ), and a quinol bd oxidase ( 6 ). In addition, T. daxensis has two respiratory nitrite reductases; NirS, which reduces NO 2 − to NO, and NrfA that reduces NO 2 − to NH 4 + .…”