2c54: Difference between revisions
No edit summary |
No edit summary |
||
| Line 4: | Line 4: | ||
==Overview== | ==Overview== | ||
GDP-mannose-3',5'-epimerase (GME) from Arabidopsis thaliana catalyzes the | 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== | ==About this Structure== | ||
| Line 14: | Line 14: | ||
[[Category: GDP-mannose 3,5-epimerase]] | [[Category: GDP-mannose 3,5-epimerase]] | ||
[[Category: Single protein]] | [[Category: Single protein]] | ||
[[Category: Major, L | [[Category: Major, L L.]] | ||
[[Category: Naismith, J | [[Category: Naismith, J H.]] | ||
[[Category: Wolucka, B | [[Category: Wolucka, B A.]] | ||
[[Category: EPE]] | [[Category: EPE]] | ||
[[Category: FMT]] | [[Category: FMT]] | ||
| Line 33: | Line 33: | ||
[[Category: vitamin c]] | [[Category: vitamin c]] | ||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 16:44:58 2008'' | ||
Revision as of 17:44, 21 February 2008
|
GDP-MANNOSE-3', 5'-EPIMERASE (ARABIDOPSIS THALIANA), K178R, WITH GDP-BETA-L-GULOSE AND GDP-4-KETO-BETA-L-GULOSE BOUND IN ACTIVE SITE.
OverviewOverview
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 StructureAbout this Structure
2C54 is a Single protein structure of sequence from Arabidopsis thaliana with , , and as ligands. Active as GDP-mannose 3,5-epimerase, with EC number 5.1.3.18 Known structural/functional Site: . Full crystallographic information is available from OCA.
ReferenceReference
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 Thu Feb 21 16:44:58 2008