Title :

Bound Substrate in the Structure of Cyanobacterial Branching Enzyme Supports a New Mechanistic Model

Author(s) :

Hayashi, Mari [Auteur]
Akita University
Suzuki, Ryuichiro [Auteur]
Akita University
Colleoni, Christophe [Auteur]
Unité de Glycobiologie Structurale et Fonctionnelle - UMR 8576 [UGSF]
Ball, Steven [Auteur]
Unité de Glycobiologie Structurale et Fonctionnelle - UMR 8576 [UGSF]
Fujita, Naoko [Auteur]
Akita University
Suzuki, Eiji [Auteur]
Akita University

Journal title :

THE JOURNAL OF BIOLOGICAL CHEMISTRY

Volume number :

292

Pages :

5465-5475

Publication date :

2017-03-31

ISSN :

0021-9258

English keyword(s) :

carbohydrate biosynthesis
cyanobacteria
enzyme mechanism
enzyme structure
glycogen
branching enzyme
starch
surface binding site

HAL domain(s) :

Chimie/Chimie théorique et/ou physique

English abstract : [en]

Branching enzyme (BE) catalyzes the formation of α-1,6-glucosidic linkages in amylopectin and glycogen. The reaction products are variable, depending on the organism sources, and the mechanistic basis for these different ...
Show more >Branching enzyme (BE) catalyzes the formation of α-1,6-glucosidic linkages in amylopectin and glycogen. The reaction products are variable, depending on the organism sources, and the mechanistic basis for these different outcomes is unclear. Although most cyanobacteria have only one BE isoform belonging to glycoside hydrolase family 13, Cyanothece sp. ATCC 51142 has three isoforms (BE1, BE2, and BE3) with distinct enzymatic properties, suggesting that investigations of these enzymes might provide unique insights into this system. Here, we report the crystal structure of ligand-free wild-type BE1 (residues 5–759 of 1–773) at 1.85 Å resolution. The enzyme consists of four domains, including domain N, carbohydrate-binding module family 48 (CBM48), domain A containing the catalytic site, and domain C. The central domain A displays a (β/α)8-barrel fold, whereas the other domains adopt β-sandwich folds. Domain N was found in a new location at the back of the protein, forming hydrogen bonds and hydrophobic interactions with CBM48 and domain A. Site-directed mutational analysis identified a mutant (W610N) that bound maltoheptaose with sufficient affinity to enable structure determination at 2.30 Å resolution. In this structure, maltoheptaose was bound in the active site cleft, allowing us to assign subsites −7 to −1. Moreover, seven oligosaccharide-binding sites were identified on the protein surface, and we postulated that two of these in domain A served as the entrance and exit of the donor/acceptor glucan chains, respectively. Based on these structures, we propose a substrate binding model explaining the mechanism of glycosylation/deglycosylation reactions catalyzed by BE.Show less >

Language :

Anglais

Audience :

Non spécifiée

Administrative institution(s) :

CNRS
Université de Lille

Collections :

• Unité de Glycobiologie Structurale et Fonctionnelle (UGSF) - UMR 8576

Research team(s) :

Génétique microbienne

Submission date :

2020-02-12T15:45:14Z
2021-05-20T09:14:08Z