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Journal of Biochemistry Advance Access originally published online on March 23, 2009
Journal of Biochemistry 2009 146(1):95-102; doi:10.1093/jb/mvp051
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© The Authors 2009. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved

Highly Thermostable L-Threonine Dehydrogenase from the Hyperthermophilic Archaeon Thermococcus kodakaraensis

Qamar Bashir1, Naeem Rashid1, Farrukh Jamil1, Tadayuki Imanaka2 and Muhammad Akhtar1,3,*

1School of Biological Sciences, University of the Punjab, Quaid-e-Azam Campus, Lahore 54590, Pakistan; 2College of Life Sciences, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatu, Shiga 525-8577, Japan; and 3School of Biological Sciences, University of Southampton, Southampton SO16 7PX, UK

*To whom correspondence should be addressed. Tel: +44-23-8059-4338, Fax: +44-23-8059-4459, E-mail: ma3{at}soton.ac.uk

Received December 16, 2008; Accepted March 6, 2009


  Abstract

L-Threonine dehydrogenase, a key enzyme in the L-threonine metabolism, catalyses the NAD+-dependent conversion of L-threonine to 2-amino-3-ketobutyrate, that non-enzymically decarboxylates to aminoacetone. A search of the genome sequence of hyperthermophilic archaeon, Thermococcus kodakaraensis revealed the presence of a closely related orthologue (TK0916) of archaeal and bacterial L-threonine dehydrogenase genes. Expression in Escherichia coli, purification and characterization of the TK0916 gene product revealed that this gene actually coded for a protein with high levels of L-threonine dehydrogenase activity (7.26 U mg–1). The enzyme exhibited highest activity at pH 12 and 90°C. The Km values for L-threonine and NAD+ at 50°C were 1.6 mM and 0.028 mM, respectively. The enzyme activity was dependent on divalent cations. The half-life of the enzyme was more than 2 h at 85°C and 24 min in boiling water. This is the most thermostable threonine dehydrogenase exhibiting optimal activity at the highest pH (12) reported to date. This is the first report on the characterization of a TDH from genus Thermococcus.

Key Words: hyperthermophilic archaea, thermostable L-threonine dehydrogenase, Thermococcus kodakaraensis


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