InterPro: IPR004661 L-ribulose-5-phosphate 4-epimerase

L-ribulose-phosphate 4-epimerase (phosphoribulose isomerase) converts L-ribulose 5-phosphate to D-xylulose 5-phosphate. The structure of L-ribulose-5-phosphate 4-epimerase from Escherichia coli has been solved to 2.4 A resolution. The structure is homo-tetrameric and displays C(4) symmetry. Each subunit has a single domain comprised of a central beta-sheet flanked on either side by layers of alpha-helices. The active site is identified by the position of the catalytic zinc residue and is located at the interface between two adjacent subunits. A remarkable feature of the structure is that it shows a very close resemblance to that of L-fuculose-1-phosphate aldolase, IPR004782. This is consistent with the notion that both enzymes belong to a superfamily of epimerases/aldolases that catalyse carbon-carbon bond cleavage reactions via a metal-stabilised enolate intermediate. Detailed inspection of the epimerase structure, however, indicates that despite the close overall structural similarity to class II aldolases, the enzyme has evolved distinct active site features that promote its particular chemistry [1].