Affiliation:
1. Mikrobiologie, Fakultät Biologie, Albert-Ludwigs-Universität, Freiburg, Germany
Abstract
ABSTRACT
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.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
47 articles.
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