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'''GDP-MANNOSE-3', 5'-EPIMERASE (ARABIDOPSIS THALIANA), K217A, WITH GDP-ALPHA-D-MANNOSE BOUND IN THE ACTIVE SITE.''' | '''GDP-MANNOSE-3', 5'-EPIMERASE (ARABIDOPSIS THALIANA), K217A, WITH GDP-ALPHA-D-MANNOSE BOUND IN THE ACTIVE SITE.''' | ||
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[[Category: Wolucka, B A.]] | [[Category: Wolucka, B A.]] | ||
[[Category: 3' 5'-epimerase]] | [[Category: 3' 5'-epimerase]] | ||
[[Category: | [[Category: Ascorbate biosynthesis]] | ||
[[Category: | [[Category: Gdp-galactose]] | ||
[[Category: | [[Category: Gdp-gulose]] | ||
[[Category: | [[Category: Gdp-mannose]] | ||
[[Category: | [[Category: Isomerase]] | ||
[[Category: | [[Category: Keto intermediate]] | ||
[[Category: | [[Category: Nad]] | ||
[[Category: | [[Category: Short chain dehydratase/reductase]] | ||
[[Category: | [[Category: Vitamin c]] | ||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 21:16:45 2008'' | |||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | |||
Revision as of 18:16, 3 May 2008
GDP-MANNOSE-3', 5'-EPIMERASE (ARABIDOPSIS THALIANA), K217A, WITH GDP-ALPHA-D-MANNOSE 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
2C5E is a Single protein structure of sequence from Arabidopsis thaliana. 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 Page seeded by OCA on Sat May 3 21:16:45 2008
