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3bc9
From Proteopedia
Alpha-amylase B in complex with acarbose
Overview
The gene for a membrane-bound, halophilic, and thermostable alpha-amylase, AmyB, from Halothermothrix orenii was cloned and sequenced. The crystal structure shows that, in addition to the typical domain organization of family 13 glycoside hydrolases, AmyB carries an additional N-terminal domain (N domain) that forms a large groove--the N-C groove--some 30 A away from the active site. The structure of AmyB with the inhibitor acarbose at 1.35 A resolution shows that a nonasaccharide has been synthesized through successive transglycosylation reactions of acarbose. Unexpectedly, in a complex of wild-type AmyB with alpha-cyclodextrin and maltoheptaose at 2.2 A resolution, a maltotetraose molecule is bound in subsites -1 to +3, spanning the cleavage point at -1/+1, with the -1 glucosyl residue present as a (2)S(o) skew boat. This wild-type AmyB complex was obtained in the presence of a large excess of substrate, a condition under which it is possible to capture Michaelis complexes, which may explain the observed binding across -1/+1 and ring distortion. We observe three methionine side chains that serve as "binding platforms" for glucosyl rings in AmyB, a seemingly rare occurrence in carbohydrate-binding proteins. The structures and results from the biochemical characterization of AmyB and AmyB lacking the N domain show that the N domain increases binding of the enzyme to raw starch. Furthermore, theoretical modeling suggests that the N-C groove can accommodate, spatially and chemically, large substrates such as A-starch.
About this Structure
3BC9 is a Single protein structure of sequence from Halothermothrix orenii. Full crystallographic information is available from OCA.
Reference
Crystal structure of the polyextremophilic alpha-amylase AmyB from Halothermothrix orenii: details of a productive enzyme-substrate complex and an N domain with a role in binding raw starch., Tan TC, Mijts BN, Swaminathan K, Patel BK, Divne C, J Mol Biol. 2008 May 9;378(4):850-68. Epub 2008 Feb 29. PMID:18387632 Page seeded by OCA on Thu Apr 24 09:48:10 2008
