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Journal of Bacteriology, October 2009, p. 6352-6362, Vol. 191, No. 20
0021-9193/09/$08.00+0     doi:10.1128/JB.00794-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Malonic Semialdehyde Reductase, Succinic Semialdehyde Reductase, and Succinyl-Coenzyme A Reductase from Metallosphaera sedula: Enzymes of the Autotrophic 3-Hydroxypropionate/4-Hydroxybutyrate Cycle in Sulfolobales{triangledown}

Daniel Kockelkorn and Georg Fuchs*

Mikrobiologie, Fakultät für Biologie, Universität Freiburg, Freiburg, Germany

Received 18 June 2009/ Accepted 5 August 2009

A 3-hydroxypropionate/4-hydroxybutyrate cycle operates during autotrophic CO2 fixation in various members of the Crenarchaea. In this cycle, as determined using Metallosphaera sedula, malonyl-coenzyme A (malonyl-CoA) and succinyl-CoA are reductively converted via their semialdehydes to the corresponding alcohols 3-hydroxypropionate and 4-hydroxybutyrate. Here three missing oxidoreductases of this cycle were purified from M. sedula and studied. Malonic semialdehyde reductase, a member of the 3-hydroxyacyl-CoA dehydrogenase family, reduces malonic semialdehyde with NADPH to 3-hydroxypropionate. The latter compound is converted via propionyl-CoA to succinyl-CoA. Succinyl-CoA reduction to succinic semialdehyde is catalyzed by malonyl-CoA/succinyl-CoA reductase, a promiscuous NADPH-dependent enzyme that is a paralogue of aspartate semialdehyde dehydrogenase. Succinic semialdehyde is then reduced with NADPH to 4-hydroxybutyrate by succinic semialdehyde reductase, an enzyme belonging to the Zn-dependent alcohol dehydrogenase family. Genes highly similar to the Metallosphaera genes were found in other members of the Sulfolobales. Only distantly related genes were found in the genomes of autotrophic marine Crenarchaeota that may use a similar cycle in autotrophic carbon fixation.

* Corresponding author. Mailing address: Mikrobiologie, Fakultät Biologie, Schänzlestr. 1, D-79104 Freiburg, Germany. Phone: 49-761-2032649. Fax: 49-761-2032626. E-mail: georg.fuchs{at}biologie.uni-freiburg.de

{triangledown} Published ahead of print on 14 August 2009.

Journal of Bacteriology, October 2009, p. 6352-6362, Vol. 191, No. 20
0021-9193/09/$08.00+0     doi:10.1128/JB.00794-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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