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'''ACETOHYDROXYACID ISOMEROREDUCTASE COMPLEXED WITH ITS REACTION PRODUCT DIHYDROXY-METHYLVALERATE, MANGANESE AND ADP-RIBOSE.''' | '''ACETOHYDROXYACID ISOMEROREDUCTASE COMPLEXED WITH ITS REACTION PRODUCT DIHYDROXY-METHYLVALERATE, MANGANESE AND ADP-RIBOSE.''' | ||
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[[Category: Halgand, F.]] | [[Category: Halgand, F.]] | ||
[[Category: Thomazeau, K.]] | [[Category: Thomazeau, K.]] | ||
[[Category: | [[Category: Adp-ribose]] | ||
[[Category: | [[Category: Branched chain amino acid biosynthesis]] | ||
[[Category: | [[Category: Manganese]] | ||
[[Category: | [[Category: Oxidoreductase]] | ||
[[Category: | [[Category: Reaction product]] | ||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 06:26:59 2008'' | |||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on | |||
Revision as of 06:27, 3 May 2008
ACETOHYDROXYACID ISOMEROREDUCTASE COMPLEXED WITH ITS REACTION PRODUCT DIHYDROXY-METHYLVALERATE, MANGANESE AND ADP-RIBOSE.
OverviewOverview
Acetohydroxyacid isomeroreductase catalyses a two-step reaction composed of an alkyl migration followed by an NADPH-dependent reduction. Both steps require a divalent cation and the first step has a strong preference for magnesium. Manganese ions are highly unfavourable to the reaction: only 3% residual activity is observed in the presence of this cation. Acetohydroxyacid isomeroreductase has been crystallized with its substrate, 2-aceto-2-hydroxybutyrate (AHB), Mn(2+) and NADPH. The 1.6 A resolution electron-density map showed the reaction product (2,3-dihydroxy-3-methylvalerate, DHMV) and a density corresponding to (phospho)-ADP-ribose instead of the whole NADP(+). This is one of the few structures of an enzyme complexed with its reaction product. The structure of this complex was refined to an R factor of 19.3% and an R(free) of 22.5%. The overall structure of the enzyme is very similar to that of the complex with the reaction-intermediate analogue IpOHA [N-hydroxy-N-isopropyloxamate; Biou et al. (1997), EMBO J. 16, 3405-3415]. However, the active site shows some differences: the nicotinamide is cleaved and the surrounding amino acids have rearranged accordingly. Comparison between the structures corresponding to the reaction intermediate and to the end of the reaction allowed the proposal of a reaction scheme. Taking this result into account, the enzyme was crystallized with Ni(2+) and Zn(2+), for which only 0.02% residual activity were measured; however, the crystals of AHB/Zn/NADPH and of AHB/Ni/NADPH also contain the reaction product. Moreover, mass-spectrometry measurements confirmed the -cleavage of nicotinamide.
About this StructureAbout this Structure
1QMG is a Single protein structure of sequence from Spinacia oleracea. Full crystallographic information is available from OCA.
ReferenceReference
Structure of spinach acetohydroxyacid isomeroreductase complexed with its reaction product dihydroxymethylvalerate, manganese and (phospho)-ADP-ribose., Thomazeau K, Dumas R, Halgand F, Forest E, Douce R, Biou V, Acta Crystallogr D Biol Crystallogr. 2000 Apr;56(Pt 4):389-97. PMID:10739911 Page seeded by OCA on Sat May 3 06:26:59 2008