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- Title
Crystal structure of the branching enzyme I (BEI) from Oryza sativa L with implications for catalysis and substrate binding.
- Authors
Noguchi, Junji; Chaen, Kimiko; Vu, Nhuan Thi; Akasaka, Taiki; Shimada, Hiroaki; Nakashima, Takashi; Nishi, Aiko; Satoh, Hikaru; Omori, Toshiro; Kakuta, Yoshimitsu; Kimura, Makoto
- Abstract
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.
- Subjects
MOLECULAR structure; RICE; PLANT enzymes; CATALYSIS; PLANT growing media; STARCH; POLYSACCHARIDES; CARBOHYDRATES
- Publication
Glycobiology, 2011, Vol 21, Issue 8, p1108
- ISSN
0959-6658
- Publication type
Article
- DOI
10.1093/glycob/cwr049