6-phosphogluconate dehydrogenase (1.1.1.44) catalyses the oxidative decarboxylation of 6-phosphogluconate to ribulose 5-phosphate with the concomitant reduction of NADP to NADPH. The metazoan 6PGDHs have a well-conserved glycine-serine rich sequence at the C terminus, which is lacking from bacterial enzymes and from those of the parasitic protozoan Trypanosoma brucei. The active dimer of the mammalian enzyme assembles with the C-terminal tail of one subunit threaded through the other, forming part of the substrate-binding site. The tail of T. brucei 6PGDH is shorter than that of the mammalian enzyme and its terminal residues associate tightly with the second monomer. The three-dimensional structure shows this generates additional interactions between the subunits close to the active site; the coenzyme-binding domain is thereby associated more tightly with the helical domain. Three residues, conserved in all other known sequences, are important in creating a salt bridge between monomers close to the substrate-binding site [1].

This domain is structurally similar to domains found in several different families, including those represented by mannitol 2-dehydrogenase, acetohydroxy acid isomeroreductase, short chain L-3-hydroxyacyl CoA dehydrogenase, UDP-glucose/GDP-mannose dehydrogenase (dimerisation domain), N-(1-D-carboxylethyl)-L-norvaline dehydrogenase, glycerol-3-phosphate dehydrogenase, and ketopantoate reductase (PanE).

1. A 2.8 A resolution structure of 6-phosphogluconate dehydrogenase from the protozoan parasite Trypanosoma brucei: comparison with the sheep enzyme accounts for differences in activity with coenzyme and substrate analogues. J. Mol. Biol. 282, 667-81

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