Best poster award at EMBO Workshop
New membrane complex highlighted at workshop on Microbial Sulfur Metabolism
At the last EMBO Workshop on Microbial Sulfur Metabolism, held in Noordwijkerhout (The Netherlands, 15-18 April), Sofia Venceslau, Post Doc at the Bacterial Energy Metabolism Laboratory at ITQB, was awarded the Best Poster prize for her work reporting the biochemical and functional characterization of a new membrane-bound complex involved in the respiratory chain of sulfate reducing bacteria like Desulfovibrio vulgaris. This quinone-reductase complex links the soluble cytochrome c pool with the membrane menaquinone pool and has thus a crucial role in sulfate respiration.
The EMBO Workshop on Microbial Sulfur Metabolism addresses different aspects of microbial contribution to sulfur transformations, ranging from Geochemistry and Evolution, Ecology and Physiology of Sulfur Bacteria, Microbial interactions and Symbiosis, to Biotechnological applications. The conference takes place every three years, and in 2012 was organized by Gerard Muyzer (Delft University of Technology) and Alfons Stams (Wageningen University).
Qrc, a new membrane-bound complex involved in the respiratory chain of deltaproteobacterial sulfate reducers
Sofia S. Venceslau and Inês A. C. Pereira
Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal
The respiratory chain of sulfate-reducing bacteria is very distinct from other organisms, and the mechanisms of energy conservation, which have not been clearly established, involve several novel respiratory membrane complexes. Here we describe the isolation and characterization of a new respiratory complex from the membranes of Desulfovibrio vulgaris Hildenborough, named Quinone-reductase complex (Qrc) . It is composed of four subunits, QrcABCD, including a hexaheme cytochrome c (QrcA), a large protein of the molybdopterin oxidoreductase family, but which does not bind molybdenum (QrcB), a periplasmic iron-sulfur protein (QrcC) and an integral membrane protein of the NrfD family (QrcD). The QrcBCD subunits are closely related with members of the complex iron-sulfur molybdoenzyme (CISM) family (also known as DMSO reductase family) . The Qrc complex contains six c-type low-spin hemes, one [3Fe-4S]1+/0 cluster and at least three [4Fe 4S]2+/1+ clusters, and its midpoint redox potentials were determined by EPR . Functional studies with Qrc showed that it transfers electrons from the Type I cytochrome c3 (TpIc3) to the quinone pool, with the periplasmic hydrogenases (Hase) and/or formate dehydrogenases (Fdh) as primary electron donors.
Additionally, this functional association was also shown at a structural level, since Qrc can form a supercomplex with the [NiFe] Hase and TpIc3 . The qrc genes are present in deltaproteobacterial sulfate reducers that have periplasmic Hases and/or Fdhs that lack a membrane subunit for direct quinone reduction, and the qrcB gene was shown to be essential for growth with H2 or formate in D. alaskensis G20 . Thus, Qrc links the periplasmic cytochromes c to the membrane menaquinone pool. Qrc is the first respiratory complex from sulfate reducers to have its physiological function clearly elucidated, contributing to the understanding of their energy metabolism.
 Venceslau SS, Lino RR and Pereira IAC (2010) J. Biol. Chem. 285, 22774-22783
 Rothery RA, Workun GJ and Weiner JH (2008) Biochim. Biophys. Acta 1778, 1897-1929
 Venceslau SS, Matos D and Pereira IAC (2011) FEBS Lett. 585, 2177-2181
 Li XZ, Luo QW, Wofford NQ, Keller KL, McInerney MJ, Wall JD and Krumholz LR (2009) J. Bacteriol. 191, 2703-2712