2c5a

From Proteopedia

Revision as of 15:53, 5 November 2007

GDP-MANNOSE-3', 5'-EPIMERASE (ARABIDOPSIS THALIANA), Y174F, WITH GDP-BETA-L-GALACTOSE BOUND IN THE ACTIVE SITE

Overview

GDP-mannose-3',5'-epimerase (GME) from Arabidopsis thaliana catalyzes the, epimerization of both the 3' and 5' positions of GDP-alpha-D-mannose to, yield GDP-beta-L-galactose. Production of the C5' epimer of, GDP-alpha-D-mannose, GDP-beta-L-gulose, has also been reported. The, reaction occurs as part of vitamin C biosynthesis in plants. We have, determined structures of complexes of GME with GDP-alpha-D-mannose, GDP-beta-L-galactose, and a mixture of GDP-beta-L-gulose with, GDP-beta-L-4-keto-gulose to resolutions varying from 2.0 to 1.4 A. The, enzyme has the classical extended short-chain dehydratase/reductase (SDR), fold. We have confirmed that GME establishes an equilibrium between two, products, GDP-beta-L-galactose and GDP-beta-L-gulose. The reaction, proceeds by C4' oxidation of GDP-alpha-D-mannose followed by epimerization, of the C5' position to give GDP-beta-L-4-keto-gulose. This intermediate is, either reduced to give GDP-beta-L-gulose or the C3' position is epimerized, to give GDP-beta-L-4-keto-galactose, then C4' is reduced to, GDP-beta-L-galactose. The combination of oxidation, epimerization, and, reduction in a single active site is unusual. Structural analysis coupled, to site-directed mutagenesis suggests C145 and K217 as the acid/base pair, responsible for both epimerizations. On the basis of the structure of the, GDP-beta-L-gulose/GDP-beta-L-4-keto-gulose co-complex, we predict that a, ring flip occurs during the first epimerization and that a boat, intermediate is likely for the second epimerization. Comparison of GME, with other SDR enzymes known to abstract a protein alpha to the keto, function of a carbohydrate identifies key common features.

About this Structure

2C5A is a Single protein structure of sequence from Arabidopsis thaliana with GDC, NAD, BTB and FMT as ligands. Active as GDP-mannose 3,5-epimerase, with EC number 5.1.3.18 Structure known Active Site: AC1. Full crystallographic information is available from OCA.

Reference

Structure and function of GDP-mannose-3',5'-epimerase: an enzyme which performs three chemical reactions at the same active site., Major LL, Wolucka BA, Naismith JH, J Am Chem Soc. 2005 Dec 28;127(51):18309-20. PMID:16366586

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