title: Look on the positive side! The orientation, identification and bioenergetics of 'Archaeal' membrane-bound nitrate reductases.
abstract: Many species of Bacteria and Archaea respire nitrate using a molybdenum-dependent membrane-bound respiratory system called Nar. Classically, the 'Bacterial' Nar system is oriented such that nitrate reduction takes place on the inside of this membrane. However, the active site subunit of the 'Archaeal' Nar systems has a twin arginine ('RR') motif, which is a suggestion of translocation to the outside of the cytoplasmic membrane. These 'Archaeal' type of nitrate reductases are part of a group of molybdoenzymes with an 'RR' motif that are predicted to have an aspartate ligand to the molybdenum ion. This group includes selenate reductases and possible sequence signatures are described that serve to distinguish the Nar nitrate reductases from the selenate reductases. The 'RR' sequences of nitrate reductases of Archaea and some that have recently emerged in Bacteria are also considered and it is concluded that there is good evidence for there being both Archaeal and Bacterial examples of Nar-type nitrate reductases with an active site on the outside of the cytoplasmic membrane. Finally, the bioenergetic consequences of nitrate reduction on the outside of the cytoplasmic membrane have been explored.
authors: Departamento de Agroquímica y Bioquímica, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain.
authors: Rosa Maria
authors: RM
authors: Martinez-Espinosa
authors: Elizabeth J
authors: EJ
authors: Dridge
authors: Maria J
authors: MJ
authors: Bonete
authors: Julea N
authors: JN
authors: Butt
authors: Clive S
authors: CS
authors: Butler
authors: Frank
authors: F
authors: Sargent
authors: David J
authors: DJ
authors: Richardson
mesh_terms: D001105:Archaea / Q000201:enzymology*; D019843:Archaeal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001419:Bacteria / Q000201:enzymology; D002462:Cell Membrane / Q000201:enzymology*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009565:Nitrate Reductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D019843:Archaeal Proteins; D008565:Membrane Proteins; D009565:Nitrate Reductases