title: Quinone-reactive proteins devoid of haem b form widespread membrane-bound electron transport modules in bacterial respiration.
abstract: Many quinone-reactive enzyme complexes that are part of membrane-integral eukaryotic or prokaryotic respiratory electron transport chains contain one or more haem b molecules embedded in the membrane. In recent years, various novel proteins have emerged that are devoid of haem b but are thought to fulfil a similar function in bacterial anaerobic respiratory systems. These proteins are encoded by genes organized in various genomic arrangements and are thought to form widespread membrane-bound quinone-reactive electron transport modules that exchange electrons with redox partner proteins located at the outer side of the cytoplasmic membrane. Prototypic representatives are the multihaem c-type cytochromes NapC, NrfH and TorC (NapC/NrfH family), the putative iron-sulfur protein NapH and representatives of the NrfD/PsrC family. Members of these protein families vary in the number of their predicted transmembrane segments and, consequently, diverse quinone-binding sites are expected. Only a few of these enzymes have been isolated and characterized biochemically and high-resolution structures are limited. This mini-review briefly summarizes predicted and experimentally demonstrated properties of the proteins in question and discusses their role in electron transport and bioenergetics of anaerobic respiration.
authors.affiliation: Institute of Molecular Biosciences, Johann Wolfgang Goethe University, Max-von-Laue-Strasse 9, D-60438 Frankfurt am Main, Germany. simon@bio.uni-frankurt.de
authors.forename: Jörg
authors.initials: J
authors.lastname: Simon
authors.forename: Melanie
authors.initials: M
authors.lastname: Kern
mesh_terms: D018407:Bacterial Physiological Phenomena; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019069:Cell Respiration / Q000502:physiology*; D004579:Electron Transport; D006418:Heme / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011809:Quinones / Q000737:chemistry* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D011809:Quinones; D006418:Heme