Download MendeleyCrystallographic study of coenzyme, coenzyme analogue and substrate binding in 6-phosphogluconate dehydrogenase: implications for NADP specificity and the enzyme mechanism.
Adams, M.J., Ellis, G.H., Gover, S., Naylor, C.E., Phillips, C.(1994) Structure 2: 651-668
- PubMed: 7922042
- DOI: https://doi.org/10.1016/s0969-2126(00)00066-6
- Primary Citation of Related Structures:
1PGN, 1PGO, 1PGP, 1PGQ - PubMed Abstract:
The nicotinamide adenine dinucleotide phosphate (NADP)-dependent oxidative decarboxylase, 6-phosphogluconate dehydrogenase, is a major source of reduced coenzyme for synthesis. Enzymes later in the pentose phosphate pathway convert the reaction product, ribulose 5-phosphate, to ribose 5-phosphate. Crystallographic study of complexes with coenzyme and substrate explain the NADP dependence which determines the enzyme's metabolic role and support the proposed general base-general acid mechanism. The refined structures of binary coenzyme/analogue complexes show that Arg33 is ordered by binding the 2'-phosphate, and provides one face of the adenine site. The nicotinamide, while less tightly bound, is more extended when reduced than when oxidized. All substrate binding residues are conserved; the 3-hydroxyl of 6-phosphogluconate is hydrogen bonded to N zeta of Lys183 and the 3-hydrogen points towards the oxidized nicotinamide. The 6-phosphate replaces a tightly bound sulphate in the apo-enzyme. NADP specificity is achieved primarily by Arg33 which binds the 2'-phosphate but, in its absence, obscures the adenine pocket. The bound oxidized nicotinamide is syn; hydride transfer from bound substrate to the nicotinamide si- face is achieved with a small movement of the nicotinamide nucleotide. Lys183 may act as general base. A water bound to Gly130 in the coenzyme domain is the most likely acid required in decarboxylation. The dihydronicotinamide ring of NADPH competes for ligands with the 1-carboxyl of 6-phosphogluconate.
Organizational Affiliation:
University of Oxford, Laboratory of Molecular Biophysics, UK.
