2c54

From Proteopedia

gdp-mannose-3', 5' -epimerase (arabidopsis thaliana),k178r, with gdp-beta-l-gulose and gdp-4-keto-beta-l-gulose bound in active site.

Structural highlights

2c54 is a 2 chain structure with sequence from Arabidopsis thaliana. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance.
Method:	X-ray diffraction, Resolution 1.5Å
Ligands:	, , , ,
Resources:	FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT

Function

GME_ARATH Catalyzes a reversible epimerization of GDP-D-mannose that precedes the committed step in the biosynthesis of vitamin C (L-ascorbate), resulting in the hydrolysis of the highly energetic glycosyl-pyrophosphoryl linkage. Able to catalyze 2 distinct epimerization reactions and can release both GDP-L-galactose and GDP-L-gulose from GDP-mannose.^[1]

Evolutionary Conservation

Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.

Publication Abstract from PubMed

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.

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^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

References

↑ Wolucka BA, Van Montagu M. GDP-mannose 3',5'-epimerase forms GDP-L-gulose, a putative intermediate for the de novo biosynthesis of vitamin C in plants. J Biol Chem. 2003 Nov 28;278(48):47483-90. PMID:12954627 doi:10.1074/jbc.M309135200
↑ Major LL, Wolucka BA, Naismith JH. Structure and function of GDP-mannose-3',5'-epimerase: an enzyme which performs three chemical reactions at the same active site. J Am Chem Soc. 2005 Dec 28;127(51):18309-20. PMID:16366586 doi:10.1021/ja056490i