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Journal of Biochemistry 2006 139(3):591-596; doi:10.1093/jb/mvj057
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© 2006 The Japanese Biochemical Society.

Regular Paper

Catalytic Promiscuity in Dihydroxy-Acid Dehydratase from the Thermoacidophilic Archaeon Sulfolobus solfataricus

Seonghun Kim1,2 and Sun Bok Lee1,2,3,*

1 School of Environmental Science and Engineering, 2 Division of Molecular Life and Sciences, and 3 Department of Chemical Engineering, Pohang University of Science and Technology, San 31, Hyoja-dong, Pohang 790-784, Korea

* To whom correspondence should be addressed. Tel: +82-54-279-2268, Fax: +82-54-279-5528, E-mail: sblee{at}postech.ac.kr

Dihydroxy-acid dehydratase (DHAD) is one of the key enzymes involved in the biosynthetic pathway of the branched chain amino acids. Although the enzyme has been purified and characterized in various mesophiles, including bacteria and eukarya, the biochemical properties of DHAD from hyperthermophilic archaea have not yet been reported. In this study we cloned, expressed in Escherichia coli, and purified a DHAD homologue from the thermoacidophilic archaeon Sulfolobus solfataricus, which grows optimally at 80°C and pH 3. The recombinant S. solfataricus DHAD (rSso_DHAD) showed the highest activity on 2,3-dihydroxyisovalerate among 17 aldonic acids tested. Interestingly, this enzyme also displayed high activity toward D-gluconate and some other pentonic and hexonic sugar acids. The kcat/Km values were 140.3 mM–1 s–1 for 2,3-dihydroxyisovalerate and 20.0 mM–1 s–1 for D-gluconate, respectively. A possible evolutionary explanation for substrate promiscuity was provided through amino acid sequence alignments of DHADs and 6-phosphogluconate dehydratases from archaea, bacteria and eukarya.


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