The cyclization mechanism of cyclodextrin glycosyltransferase (CGTase) as revealed by a gamma-cyclodextrin-CGTase complex at 1.8-A resolution.
The enzyme cyclodextrin glycosyltransferase is closely related to alpha-amylases but has the unique ability to produce cyclodextrins (circular alpha(1-->4)-linked glucoses) from starch. To characterize this specificity we determined a 1.8-A structure of an E257Q/D229N mutant cyclodextrin glycosyltransferase in complex with its product gamma-cyclodextrin, which reveals for the first time how cyclodextrin is competently bound. Across subsites -2, -1, and +1, the cyclodextrin ring binds in a twisted mode similar to linear sugars, giving rise to deformation of its circular symmetry. At subsites -3 and +2, the cyclodextrin binds in a manner different from linear sugars. Sequence comparisons and site-directed mutagenesis experiments support the conclusion that subsites -3 and +2 confer the cyclization activity in addition to subsite -6 and Tyr-195. On this basis, a role of the individual residues during the cyclization reaction cycle is proposed.
Uitdehaag
J C
JC
BIOSON Research Institute, Laboratory of Biophysical Chemistry, Groningen Biomolecular Sciences, University of Groningen, Nijenborgh 4, 9747AG Groningen, the Netherlands.
Kalk
K H
KH
van Der Veen
B A
BA
Dijkhuizen
L
L
Dijkstra
B W
BW
D001407:Bacillus / Q000201:enzymology; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D003505:Cyclodextrins / Q000737:chemistry* / Q000378:metabolism*; D005964:Glucosyltransferases / Q000378:metabolism*; D008958:Models, Molecular; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D000516:alpha-Amylases / Q000378:metabolism; D047408:gamma-Cyclodextrins
D001426:Bacterial Proteins; D003505:Cyclodextrins; D009844:Oligosaccharides; D047408:gamma-Cyclodextrins; C101184:maltononaose; D005964:Glucosyltransferases; C019963:cyclomaltodextrin glucanotransferase; D000516:alpha-Amylases; C023792:gamma-cyclodextrin