Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 292, Issue 13, Pages 5465-5475Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M116.755629
Keywords
-
Categories
Funding
- Shimadzu Science Foundation [120003]
- JSPS KAKENHI [15K18685, 16K07467]
- Grants-in-Aid for Scientific Research [15K18685, 16K07467] Funding Source: KAKEN
Ask authors/readers for more resources
Branching enzyme (BE) catalyzes the formation of alpha-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 angstrom 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 (beta/alpha)(8)-barrel fold, whereas the other domains adopt beta-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 angstrom 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.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available