21169482
not annotated - annotated - LINNAEUS only
Identification of missing genes and enzymes for autotrophic carbon fixation in crenarchaeota.
Two autotrophic carbon fixation cycles have been identified in Crenarchaeota. The dicarboxylate/4-hydroxybutyrate cycle functions in anaerobic or microaerobic autotrophic members of the Thermoproteales and Desulfurococcales. The 3-hydroxypropionate/4-hydroxybutyrate cycle occurs in aerobic autotrophic Sulfolobales; a similar cycle may operate in autotrophic aerobic marine Crenarchaeota. Both cycles form succinyl-coenzyme A (CoA) from acetyl-CoA and two molecules of inorganic carbon, but they use different means. Both cycles have in common the (re)generation of acetyl-CoA from succinyl-CoA via identical intermediates. Here, we identified several missing enzymes/genes involved in the seven-step conversion of succinyl-CoA to two molecules of acetyl-CoA in Thermoproteus neutrophilus (Thermoproteales), Ignicoccus hospitalis (Desulfurococcales), and Metallosphaera sedula (Sulfolobales). The identified enzymes/genes include succinyl-CoA reductase, succinic semialdehyde reductase, 4-hydroxybutyrate-CoA ligase, bifunctional crotonyl-CoA hydratase/(S)-3-hydroxybutyryl-CoA dehydrogenase, and beta-ketothiolase. 4-Hydroxybutyryl-CoA dehydratase, which catalyzes a mechanistically intriguing elimination of water, is well conserved and rightly can be considered the key enzyme of these two cycles. In contrast, several of the other enzymes evolved from quite different sources, making functional predictions based solely on genome interpretation difficult, if not questionable.
Ann file
T1 Species 859 885 Thermoproteus neutrophilus
N1 Reference T1 Taxonomy:70771
T2 Species 905 926 Ignicoccus hospitalis
N2 Reference T2 Taxonomy:160233
T3 Species 952 973 Metallosphaera sedula
N3 Reference T3 Taxonomy:43687