Crystal structure of the branching enzyme I (BEI) from Oryza sativa L with implications for catalysis and substrate binding
| Autor: | Hikaru Satoh, Makoto Kimura, Aiko Nishi, Toshiro Omori, Taiki Akasaka, Hiroaki Shimada, Nhuan Thi Vu, Junji Noguchi, Takashi Nakashima, Yoshimitsu Kakuta, Kimiko Chaen |
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| Rok vydání: | 2011 |
| Předmět: |
Models
Molecular Binding Sites Pullulanase biology Chemistry Stereochemistry Oryza Crystal structure Crystallography X-Ray Cleavage (embryo) Biochemistry Substrate Specificity Enzyme Activation Enzyme activator 1 4-alpha-Glucan Branching Enzyme Biocatalysis Glycogen branching enzyme biology.protein Transferase Molecular replacement Binding site |
| Zdroj: | Glycobiology. 21:1108-1116 |
| ISSN: | 1460-2423 0959-6658 |
| DOI: | 10.1093/glycob/cwr049 |
| Popis: | Starch-branching enzyme catalyzes the cleavage of α-1, 4-linkages and the subsequent transfer of α-1,4 glucan to form an α-1,6 branch point in amylopectin. Sequence analysis of the rice-branching enzyme I (BEI) indicated a modular structure in which the central α-amylase domain is flanked on each side by the N-terminal carbohydrate-binding module 48 and the α-amylase C-domain. We determined the crystal structure of BEI at a resolution of 1.9 Å by molecular replacement using the Escherichia coli glycogen BE as a search model. Despite three modular structures, BEI is roughly ellipsoidal in shape with two globular domains that form a prominent groove which is proposed to serve as the α-polyglucan-binding site. Amino acid residues Asp344 and Glu399, which are postulated to play an essential role in catalysis as a nucleophile and a general acid/base, respectively, are located at a central cleft in the groove. Moreover, structural comparison revealed that in BEI, extended loop structures cause a narrowing of the substrate-binding site, whereas shortened loop structures make a larger space at the corresponding subsite in the Klebsiella pneumoniae pullulanase. This structural difference might be attributed to distinct catalytic reactions, transglycosylation and hydrolysis, respectively, by BEI and pullulanase. |
| Databáze: | OpenAIRE |
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