Identification of a thiamin-dependent synthase in Escherichia coli required for the formation of the 1-deoxy- d -xylulose 5-phosphate precursor to isoprenoids, thiamin, and pyridoxol

Georg A. Sprenger1, Ulrich Schörken1, Thomas Wiegert1, Sigrid Grolle1, Albert A. de Graaf1, Sean V. Taylor1, Tadhg P. Begley1, Stephanie Bringer‐Meyer1, Hermann Sahm1
1Institut für Biotechnologie 1 des Forschungszentrums Jülich, P.O. Box 1913, D-52425 Jülich, Germany; and Department of Chemistry, Cornell University, Ithaca, NY 14853

Tóm tắt

In Escherichia coli , 1-deoxy- d -xylulose (or its 5-phosphate, DXP) is the biosynthetic precursor to isopentenyl diphosphate [Broers, S. T. J. (1994) Dissertation (Eidgenössische Technische Hochschule, Zürich)], thiamin, and pyridoxol [Himmeldirk, K., Kennedy, I. A., Hill, R. E., Sayer, B. G. & Spenser, I. D. (1996) Chem. Commun . 1187–1188]. Here we show that an open reading frame at 9 min on the chromosomal map of E. coli encodes an enzyme ( d eoxy x ylulose-5- p hosphate synthase, DXP synthase) that catalyzes a thiamin diphosphate-dependent acyloin condensation reaction between C atoms 2 and 3 of pyruvate and glyceraldehyde 3-phosphate to yield DXP. We have cloned and overexpressed the gene ( dxs ), and the enzyme was purified 17-fold to a specific activity of 0.85 unit/mg of protein. The reaction catalyzed by DXP synthase yielded exclusively DXP, which was characterized by 1 H and 31 P NMR spectroscopy. Although DXP synthase of E. coli shows sequence similarity to both transketolases and the E1 subunit of pyruvate dehydrogenase, it is a member of a distinct protein family, and putative DXP synthase sequences appear to be widespread in bacteria and plant chloroplasts.

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