title: AMP-forming acetyl coenzyme A synthetase in the outermost membrane of the hyperthermophilic crenarchaeon Ignicoccus hospitalis.
abstract: Ignicoccus hospitalis, a hyperthermophilic, chemolithoautotrophic crenarchaeon was found to possess a new CO(2) fixation pathway, the dicarboxylate/4-hydroxybutyrate cycle. The primary acceptor molecule for this pathway is acetyl coenzyme A (acetyl-CoA), which is regenerated in the cycle via the characteristic intermediate 4-hydroxybutyrate. In the presence of acetate, acetyl-CoA can alternatively be formed in a one-step mechanism via an AMP-forming acetyl-CoA synthetase (ACS). This enzyme was identified after membrane preparation by two-dimensional native PAGE/SDS-PAGE, followed by matrix-assisted laser desorption ionization-time of flight tandem mass spectrometry and N-terminal sequencing. The ACS of I. hospitalis exhibits a molecular mass of ∼690 kDa with a monomeric molecular mass of 77 kDa. Activity tests on isolated membranes and bioinformatic analyses indicated that the ACS is a constitutive membrane-associated (but not an integral) protein complex. Unexpectedly, immunolabeling on cells of I. hospitalis and other described Ignicoccus species revealed that the ACS is localized at the outermost membrane. This perfectly coincides with recent results that the ATP synthase and the H(2):sulfur oxidoreductase complexes are also located in the outermost membrane of I. hospitalis. These results imply that the intermembrane compartment of I. hospitalis is not only the site of ATP synthesis but may also be involved in the primary steps of CO(2) fixation.
authors.affiliation: Institute for Microbiology and Archaeal Centre, Universität Regensburg, Regensburg, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Mayer
authors.forename: Ulf
authors.initials: U
authors.lastname: Küper
authors.forename: Carolin
authors.initials: C
authors.lastname: Meyer
authors.forename: Stefanie
authors.initials: S
authors.lastname: Daxer
authors.forename: Volker
authors.initials: V
authors.lastname: Müller
authors.forename: Reinhard
authors.initials: R
authors.lastname: Rachel
authors.forename: Harald
authors.initials: H
authors.lastname: Huber
mesh_terms: D000106:Acetate-CoA Ligase / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D000249:Adenosine Monophosphate / Q000378:metabolism*; D019843:Archaeal Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D019620:Desulfurococcaceae / Q000201:enzymology* / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D008565:Membrane Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D008853:Microscopy; D008954:Models, Biological; D008970:Molecular Weight; D055503:Protein Multimerization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D019843:Archaeal Proteins; D008565:Membrane Proteins; D000249:Adenosine Monophosphate; D000106:Acetate-CoA Ligase