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'''BACILLUS CIRCULANS STRAIN 251 CYCLODEXTRIN GLYCOSYLTRANSFERASE IN COMPLEX WITH MALTOHEXAOSE''' | '''BACILLUS CIRCULANS STRAIN 251 CYCLODEXTRIN GLYCOSYLTRANSFERASE IN COMPLEX WITH MALTOHEXAOSE''' | ||
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[[Category: Dijkstra, B W.]] | [[Category: Dijkstra, B W.]] | ||
[[Category: Uitdehaag, J C.M.]] | [[Category: Uitdehaag, J C.M.]] | ||
[[Category: | [[Category: Alpha-amylase]] | ||
[[Category: | [[Category: Catalysis]] | ||
[[Category: | [[Category: Cyclodextrin]] | ||
[[Category: | [[Category: Family 13 glycosyl hydrolase]] | ||
[[Category: | [[Category: Induced fit]] | ||
[[Category: | [[Category: Maltohexaose]] | ||
[[Category: | [[Category: Oligosaccharide]] | ||
[[Category: | [[Category: Transferase]] | ||
[[Category: | [[Category: Transglycosylation]] | ||
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 15:20:12 2008'' | |||
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Revision as of 15:20, 2 May 2008
BACILLUS CIRCULANS STRAIN 251 CYCLODEXTRIN GLYCOSYLTRANSFERASE IN COMPLEX WITH MALTOHEXAOSE
OverviewOverview
The enzymes from the alpha-amylase family all share a similar alpha-retaining catalytic mechanism but can have different reaction and product specificities. One family member, cyclodextrin glycosyltransferase (CGTase), has an uncommonly high transglycosylation activity and is able to form cyclodextrins. We have determined the 2.0 and 2.5 A X-ray structures of E257A/D229A CGTase in complex with maltoheptaose and maltohexaose. Both sugars are bound at the donor subsites of the active site and the acceptor subsites are empty. These structures mimic a reaction stage in which a covalent enzyme-sugar intermediate awaits binding of an acceptor molecule. Comparison of these structures with CGTase-substrate and CGTase-product complexes reveals three different conformational states for the CGTase active site that are characterized by different orientations of the centrally located residue Tyr 195. In the maltoheptaose and maltohexaose-complexed conformation, CGTase hinders binding of an acceptor sugar at subsite +1, which suggests an induced-fit mechanism that could explain the transglycosylation activity of CGTase. In addition, the maltoheptaose and maltohexaose complexes give insight into the cyclodextrin size specificity of CGTases, since they precede alpha-cyclodextrin (six glucoses) and beta-cyclodextrin (seven glucoses) formation, respectively. Both ligands show conformational differences at specific sugar binding subsites, suggesting that these determine cyclodextrin product size specificity, which is confirmed by site-directed mutagenesis experiments.
About this StructureAbout this Structure
1EO7 is a Single protein structure of sequence from Bacillus circulans. Full crystallographic information is available from OCA.
ReferenceReference
Structures of maltohexaose and maltoheptaose bound at the donor sites of cyclodextrin glycosyltransferase give insight into the mechanisms of transglycosylation activity and cyclodextrin size specificity., Uitdehaag JC, van Alebeek GJ, van Der Veen BA, Dijkhuizen L, Dijkstra BW, Biochemistry. 2000 Jul 4;39(26):7772-80. PMID:10869182 Page seeded by OCA on Fri May 2 15:20:12 2008