1ece
From Proteopedia
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ACIDOTHERMUS CELLULOLYTICUS ENDOCELLULASE E1 CATALYTIC DOMAIN IN COMPLEX WITH A CELLOTETRAOSE
Overview
The crystal structure of the catalytic domain of the thermostable, endocellulase E1 from Acidothermus cellulolyticus in complex with, cellotetraose has been solved by multiple isomorphous replacement and, refined at 2.4 A resolution to an R-factor of 0.18 (Rfree = 0.24). E1cd is, a member of the 4/7 superfamily of hydrolases, and as expected, its, structure is an (alpha/beta)8 barrel, which constitutes a prototype for, family 5-subfamily 1 cellulases. The cellotetraose molecule binds in a, manner consistent with the expected Michaelis complex for the, glycosylation half-reaction and reveals that all eight residues conserved, in family 5 enzymes are involved in recognition of the glycosyl group, attacked during cleavage. Whereas only three residues are conserved in the, whole 4/7 superfamily (the Asn/Glu duo and the Glu from which the name is, derived), structural comparisons show that all eight residues conserved in, family 5 have functional equivalents in the other 4/7 superfamily members, strengthening the case that mechanistic details are conserved throughout, the superfamily. On the basis of the structure, a detailed sequence of, physical steps of the cleavage mechanism is proposed. A close approach of, two key glutamate residues provides an elegant mechanism for the shift in, the pKa of the acid/base for the glycosylation and deglycosylation, half-reactions. Finally, purely structural based comparisons are used to, show that significant differences exist in structural similarity scores, resulting from different methods and suggest that caution should be, exercised in interpreting such results in terms of implied evolutional, relationships.
About this Structure
1ECE is a Single protein structure of sequence from Acidothermus cellulolyticus. Active as Cellulase, with EC number 3.2.1.4 Full crystallographic information is available from OCA.
Reference
Crystal structure of thermostable family 5 endocellulase E1 from Acidothermus cellulolyticus in complex with cellotetraose., Sakon J, Adney WS, Himmel ME, Thomas SR, Karplus PA, Biochemistry. 1996 Aug 20;35(33):10648-60. PMID:8718854
Page seeded by OCA on Tue Nov 20 13:53:30 2007
