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, 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)-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.
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http://dx.doi.org/10.1074/jbc.M116.755629 | DOI Listing |
Ying Yong Sheng Tai Xue Bao
October 2024
College of Plant Protection, Shandong Agricultural University, Tai'an 271018, Shandong, China.
We investigated the effects of exogenous abscisic acid (ABA) on grain filling, starch accumulation, and endogenous hormones in maize (both the heat-tolerant maize variety Zhengdan 958 (ZD958) and the heat-sensitive variety Xianyu 335 (XY335)) under early post-anthesis high temperature stress by simulating high temperature stress for a period of 6 to 12 days post-anthesis in 2022 and 2023. There were three treatments: spraying water at ambient temperature as the control, spraying water at high temperature, and spraying ABA at high temperature. The results showed that early post-anthesis high temperature stress resulted in a significant reduction in grain weight and yield in maize, with XY335 showing a greater reduction than ZD958.
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December 2024
Division of Molecular Microbiology and Immunology, CSIR-Central Drug Research Institute, Lucknow, India.
parasites have a complex life cycle that transitions between mosquito and mammalian hosts, and undergo continuous cellular remodeling to adapt to various drastic environments. Following hepatocyte invasion, the parasite discards superfluous organelles for intracellular replication, and the remnant organelles undergo extensive branching and mature into hepatic merozoites. Autophagy is a ubiquitous eukaryotic process that permits the recycling of intracellular components.
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December 2024
LEAF-Linking Landscape, Environment, Agriculture and Food Research Center, Instituto Superior de Agronomia, Universidade de Lisboa, Tapada da Ajuda, Lisboa, Portugal.
Wheat is an essential staple food, and its production and grain quality are affected by extreme temperature events. These effects are even more relevant considering the increasing food demand for a growing world population and the predicted augmented frequency of heat waves. This study investigated the impact of simulated heat wave (HW) conditions imposed during grain filling on starch granule characteristics, endosperm ultrastructure, and transcriptomic modulation of genes involved in starch synthesis and degradation.
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November 2024
College of Food Science and Engineering, Jilin Agricultural University, Changchun 130118, China.
Single enzymatic modifications are limited to starch. Complex modification with synergistic amylases will improve starch properties more significantly. In this study, maize starch was compound modified by β-amylase and α-glucosidase.
View Article and Find Full Text PDFDiscov Immunol
November 2024
College of Medicine and Health, University of Birmingham, Birmingham, GB, UK.
Background: Immunometabolism is a crucial determinant of immune cell function, influencing cellular activation and differentiation through metabolic pathways. The intricate interplay between metabolism and immune responses is highlighted by the distinct metabolic programs utilized by immune cells to support their functions. Of particular interest is the pentose phosphate pathway (PPP), a key metabolic pathway branching out of glycolysis that plays a pivotal role in generating NADPH and pentose sugars crucial for antioxidant defense and biosynthesis.
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