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J. Biol. Chem., Vol. 280, Issue 51, 42004-42015, December 23, 2005

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A Membrane-bound Multienzyme, Hydrogen-oxidizing, and Sulfur-reducing Complex from the Hyperthermophilic Bacterium Aquifex aeolicus^*

Marianne Guiral, Pascale Tron, Corinne Aubert, Alexandre Gloter¶, Chantal Iobbi-Nivol||, and Marie-Thérèse Giudici-Orticoni1

From the Laboratoire de Bioénergétique et Ingénierie des Protéines, IBSM-CNRS, 13402 Marseille, France, Laboratoire de Physique des Solides, CNRS-UMR 8502, Université Paris Sud, Orsay, France, ^¶International Center of Young Scientists, National Institute for Materials Science, Tsukuba 305-0044, Japan, and ^||Laboratoire de Chimie Bactérienne, Institute of Microbiology and Structural Biology-CNRS, 13420 Marseille, France

Aquifex aeolicus is a hyperthermophilic, chemolithoautotrophic, hydrogen-oxidizing, and microaerophilic bacterium growing at 85 °C. We have shown that it can grow on an H₂/S° medium and produce H₂S from sulfur in the later exponential phase. The complex carrying the sulfur reducing activity (electron transport from H₂ to S°) has been purified and characterized. It is a membrane-bound multiprotein complex containing a [NiFe] hydrogenase and a sulfur reductase connected via quinones. The sulfur reductase is encoded by an operon annotated dms (dimethyl sulfoxide reductase) that we have renamed sre and is composed of three subunits. Sequence analysis showed that it belongs to the Me₂SO reductase molybdoenzyme family and is similar to the sulfur/polysulfide/thiosulfate/tetrathionate reductases. The study of catalytic properties clearly demonstrated that it can reduce tetrathionate, sulfur, and polysulfide, but cannot reduce Me₂SO and thiosulfate, and that NADPH increases the sulfur reducing activity. To date, this is the first characterization of a supercomplex from a bacterium that couples hydrogen oxidation and sulfur reduction. The distinctive feature in A. aeolicus is the cytoplasmic localization of the sulfur reduction, which is in accordance with the presence of sulfur globules in the cytoplasm. Association of this sulfur-reducing complex with a hydrogen-oxygen pathway complex (hydrogenase I, bc₁ complex) in the membrane suggests that subcomplexes involved in respiratory chains in this bacterium are part of supramolecular organization.

Received for publication, July 22, 2005 , and in revised form, September 23, 2005.

^* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

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¹ To whom correspondence should be addressed: Laboratoire de Bioénergétique et Ingénierie des Protéines, IBSM-CNRS, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France. Tel.: 33-4-91-16-45-50; Fax: 33-4-91-16-45-78; E-mail: giudici{at}ibsm.cnrs-mrs.fr.

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