1pgq: Difference between revisions

[[Image:1pgq.jpg|left|200px]]<br /><applet load="1pgq" size="350" color="white" frame="true" align="right" spinBox="true"  

BACKGROUND: 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. RESULTS: 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. CONCLUSIONS: 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.

1PGQ is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Ovis_aries Ovis aries] with <scene name='pdbligand=SO4:'>SO4</scene> and <scene name='pdbligand=2AM:'>2AM</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Phosphogluconate_dehydrogenase_(decarboxylating) Phosphogluconate dehydrogenase (decarboxylating)], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=1.1.1.44 1.1.1.44] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1PGQ OCA].  

[[Category: Adams, M J.]]

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