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Archaea
Volume 1 (2004), Issue 4, Pages 255-262
http://dx.doi.org/10.1155/2004/608428
Research Article

Transaldolase of Methanocaldococcus jannaschii

Division of Science and Mathematics, University of Minnesota, Morris, 600 E. 4th Street, Morris, MN 56267, USA

Received 18 September 2003; Accepted 16 January 2004

Copyright © 2004 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The Methanocaldococcus jannaschii genome contains putative genes for all four nonoxidative pentose phosphate pathway enzymes. Open reading frame (ORF) MJ0960 is a member of the mipB/talC family of ‘transaldolase-like’ genes, so named because of their similarity to the well-characterized transaldolase B gene family. However, recently, it has been reported that both the mipB and the talC genes from Escherichia coli encode novel enzymes with fructose-6-phosphate aldolase activity, not transaldolase activity (Schürmann and Sprenger 2001). The same study reports that other members of the mipB/talC family appear to encode transaldolases. To confirm the function of MJ0960 and to clarify the presence of a nonoxidative pentose phosphate pathway in M. jannaschii, we have cloned ORF MJ0960 from M. jannaschii genomic DNA and purified the recombinant protein. MJ0960 encodes a transaldolase and displays no fructose-6-phosphate aldolase activity. It retained full activity for 4 h at 80 °C, and for 3 weeks at 25 °C. Methanocaldococcus jannaschii transaldolase has a maximal velocity (Vmax) of 1.0 ± 0.2 µmol min–1 mg–1 at 25 °C, whereas Vmax = 12.0 ± 0.5 µmol min–1 mg–1 at 50 °C. Apparent Michaelis constants at 50 °C were Km = 0.65 ± 0.09 mM for fructose-6-phosphate and Km = 27.8 ± 4.3 µM for erythrose-4-phosphate. When ribose-5-phosphate replaced erythrose-4-phosphate as an aldose acceptor, Vmax decreased twofold, whereas the Km was 150-fold higher. The molecular mass of the active enzyme is 271 ± 27 kDa as estimated by gel filtration, whereas the predicted monomer size is 23.96 kDa, suggesting that the native form of the protein is probably a decamer. A readily available source of thermophilic pentose phosphate pathway enzymes including transaldolase may have direct application in enzymatic biohydrogen production.