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Extremophiles. 2016 Nov;20(6):843-853. Epub 2016 Sep 2.

Characterization of two β-decarboxylating dehydrogenases from Sulfolobus acidocaldarius.

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Biotechnology Research Center, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan.
Max Planck Institute for Terrestrial Microbiology, Marburg, Germany.
Molecular Biology of Archaea, Institute of Biology II, University of Freiburg, Schaenzlestr. 1, 79104, Freiburg, Germany.
Biotechnology Research Center, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan.


Sulfolobus acidocaldarius, a hyperthermoacidophilic archaeon, possesses two β-decarboxylating dehydrogenase genes, saci_0600 and saci_2375, in its genome, which suggests that it uses these enzymes for three similar reactions in lysine biosynthesis through 2-aminoadipate, leucine biosynthesis, and the tricarboxylic acid cycle. To elucidate their roles, these two genes were expressed in Escherichia coli in the present study and their gene products were characterized. Saci_0600 recognized 3-isopropylmalate as a substrate, but exhibited slight and no activity for homoisocitrate and isocitrate, respectively. Saci_2375 exhibited distinct and similar activities for isocitrate and homoisocitrate, but no detectable activity for 3-isopropylmalate. These results suggest that Saci_0600 is a 3-isopropylmalate dehydrogenase for leucine biosynthesis and Saci_2375 is a dual function enzyme serving as isocitrate-homoisocitrate dehydrogenase. The crystal structure of Saci_0600 was determined as a closed-form complex that binds 3-isopropylmalate and Mg2+, thereby revealing the structural basis for the extreme thermostability and novel-type recognition of the 3-isopropyl moiety of the substrate.


3-Isopropylmalate dehydrogenase; Crystal structure; Homoisocitrate dehydrogenase; Isocitrate dehydrogenase; Sulfolobus acidocaldarius; β-Decarboxylating dehydrogenase

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