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Journal of Biochemistry Advance Access published online on February 4, 2008
Journal of Biochemistry, doi:10.1093/jb/mvn012
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© 2008 The Japanese Biochemical Society

Characterisation of dihydrodipicolinate reductase from Thermotoga maritima reveals evolution of substrate binding kinetics

F. Grant Pearce, Clara Sprissler and Juliet A. Gerrard

School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch 8020, New Zealand

Correspondence to be sent to Dr Grant Pearce, School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch 8020, New Zealand, fax: +64-3-364-2590, email: grant.pearce{at}canterbury.ac.nz

Received January 6, 2008; Accepted January 16, 2008


  Abstract

In lysine biosynthesis, dihydrodipicolinate reductase (DHDPR) catalyses the formation of tetrahydrodipicolinate. Unlike DHDPR enzymes from E. coli and M. tuberculosis, which have dual specificity for both NADH and NADPH as cofactors, the enzyme from T. maritima has a significantly greater affinity for NADPH. Despite low sequence identity with the E. coli and M. tuberculosis DHDPR enzymes, DHDPR from T. maritima has a similar catalytic site, with many conserved residues involved in interactions with substrates. This suggests that as the enzyme evolved, the cofactor specifity was relaxed. Kinetic studies show that the T. maritima DHDPR enzyme is inhibited by high concentrations of its substrate, DHDP, and that at high concentrations NADH also acts as an inhibitor of the enzyme, suggesting a novel method of regulation for the lysine biosynthetic pathway. Increased thermal stability of the T. maritima DHDPR enzyme may be associated with the lack of C-terminal and N-terminal loops that are present in the E. coli DHDPR enzyme.

Key Words: Dihydrodipicolinate reductase, Lysine biosynthesis, Pyridine nucleotide specificity, Thermophilic enzymes, Thermotoga maritima


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