2cxg
From Proteopedia
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CYCLODEXTRIN GLYCOSYLTRANSFERASE COMPLEXED TO THE INHIBITOR ACARBOSE
Overview
Crystals of cyclodextrin glycosyltransferase (CGTase) from Bacillus, circulans strain 251 were soaked in buffer solutions containing the, pseudotetrasaccharide acarbose, a strong amylase- and CGTase inhibitor., The X-ray structure of the complex was elucidated at 2.5-A resolution with, a final crystallographic R value of 15.8% for all data between 8.0 and 2.5, A. Acarbose is bound near the catalytic residues Asp229, Glu257, and, Asp328. The carboxylic group of Glu257 is at hydrogen bonding distance, from the glycosidic oxygen in the scissile bond between the B and C sugars, (residue A is at the nonreducing end of the inhibitor). Asp328 makes, hydrogen bonds with the 4-amino-4,6-dideoxyglucose (residue B), and Asp229, is in a close van der Waals contact with the C1 atom of this sugar. From, this we conclude that in CGTase Glu257 acts as the proton donor and Asp229, serves as the general base or nucleophile, while Asp328 is involved in, substrate binding and may be important for elevating the pKa of Glu257. On, the basis of these results it appears that the absence of the C6-hydroxyl, group in the B sugar is responsible for the inhibitory properties of, acarbose on CGTase. This suggests that the C6-hydroxyl group of this sugar, plays an essential role in the catalytic mechanism of CGTase.(ABSTRACT, TRUNCATED AT 250 WORDS)
About this Structure
2CXG is a Single protein structure of sequence from Bacillus circulans with CA as ligand. This structure superseeds the now removed PDB entry 1CXG. Active as Cyclomaltodextrin glucanotransferase, with EC number 2.4.1.19 Structure known Active Sites: CA1, CA2, CAT, MB1, MB2 and MB3. Full crystallographic information is available from OCA.
Reference
X-ray structure of cyclodextrin glycosyltransferase complexed with acarbose. Implications for the catalytic mechanism of glycosidases., Strokopytov B, Penninga D, Rozeboom HJ, Kalk KH, Dijkhuizen L, Dijkstra BW, Biochemistry. 1995 Feb 21;34(7):2234-40. PMID:7857935
Page seeded by OCA on Mon Nov 5 18:15:04 2007
