Alternations in the chain length distribution of polysaccharides by adjusting the active sites of the 1,4-α-glucan branching enzyme.

The 1,4-α-glucan branching enzymes (GBEs, EC 2.4.1.18) catalyze the formation of new α-1,6 branching points in starch, playing an irreplaceable role in controlling the frequency and position of branch points in glucan chains, which present several potential applications in starch industry. Previously, a thermostable GBE that originates from Rhodothermus obamensis STB05 (RoGBE) is reported to be an excellent glycosyltransferase to modify the structures of starch. However, until now, how to control the length of the transferred glucan chains is still a challenge. Structural analysis of RoGBE shows that the residue at amino acid site 489 connects with the reducing end of the substrate, which may determine the chain length of binding oligosaccharides. The substitutions of Gln at this site with Arg, Glu and Gly result in alternations at catalytic activities and transglycosylation patterns of GBE. Specifically, the Q489E, and Q489R mutants had 5-10 % increases in catalytic activities, the Q489G shows that a slight decrease in activity. versus modified maltodextrin with wild-type RoGBE, maltodextrin incubated with Q489G, Q489E, and Q489R mutants show a 4.17 %-22.43 % increase in the ratio of glucan chains with DP < 13 in the oligosaccharide chains of modified maltodextrin. Crystallographic analyses and simulations were performed to reveal the structural alternations mediated by the introduced mutations. These results are important in the context of understanding the mechanism of action of the thermostable glycosyltransferase and can help develop more functional glycosyltransferases for controlling the glucan chains of polysaccharides.

The amino acid on the top of the active groove allosterically modulates product specificity of the 1,4-α-glucan branching enzyme.

The 1,4-α-glucan branching enzymes (GBEs, EC 2.4.1.18) catalyse the formation of α-1,6 branching points in starch, presenting several potential applications in modifying starch. Previous study proved that W285 is considered to act as a "switch" to stop extension of substrates in the structure of GBE from Cyanothece sp. (cceBE). In the structure of GBE from Rhodothermus obamensis STB05 (RoGBE), the amino acid 160 site is structurally similar to the W285 in cceBE. In order to explore the role of this site in RoGBE, several engineered mutants individually substituted with Arg, Phe and Ala at G160 were studied in our research. The results show that substitution with Arg and Phe increased branching activity significantly, and the ratio of short glucan chains among all oligosaccharides increased. Finally, we proposed that the G160 is a 'door model' to elucidate introduced mutagenesis that triggers and controls the length of binding glucan chains of starch.

Clinical effects of different etching modes for universal adhesives: a systematic review and meta-analysis.

BACKGROUND: To evaluate the clinical performance of universal adhesives in etch-and-rinse or self-etch application modes through meta-analysis. METHODS: A literature search was performed by two reviewers in the PubMed, Cochrane Library, and Embase databases (from January 2000 to March 2020). A total of 2,516 non-replicated records were identified and filtered. Studies that evaluated the clinical performance of universal adhesives using etch-and-rinse or self-etch mode were included. RevMan 5.3.5 (Cochrane, London, UK) was used to perform the meta-analysis. RESULTS: A total of 13 studies were included in the meta-analysis. The retention rates were higher in etch-and-rinse groups compared with self-etch groups [odds ratio (OR) =0.35, 95% confidence interval (CI): 0.18-0.71, P=0.003]. The etch-and-rinse approach also had better performance in marginal adaptation (OR =0.49, 95% CI: 0.36-0.67, P<0.001) and marginal staining (OR =0.49, 95% CI: 0.36-0.66, P<0.001). The current data showed a very low incidence rate of secondary caries or postoperative sensitivity, and there were no significant differences in the incidence rates between the etch-and-rinse groups and self-etch groups. DISCUSSION: The current evidence shows that, compared with self-etch approach, the etch-and-rinse approach for universal adhesives provides improved clinical outcomes in terms of retention rates, marginal adaptation, and marginal staining.

Dental caries and associated factors among Chinese children and adolescents: A protocol for systematic review and meta-analysis.

BACKGROUND: Dental caries is a common disease under the action of many factors. Dental caries may occur in all age groups, among which children and adolescents are at high risk of dental caries. Early identification of the risk factors of dental caries is very important for clinical staff to prevent and intervene as soon as possible and reduce the incidence of dental caries. Although Chinese scholars have studied and summarized the risk factors of dental caries in children and adolescents, the conclusions are different. Therefore, in this study, meta-analysis was used to summarize the risk factors of dental caries in Chinese children and adolescents, and to explore the characteristics of high-risk groups of dental caries, so as to provide reference for early detection and prevention of dental caries. METHODS: Medical specialty databases like PubMed, Embase, Cochrane Library, Web of Science, China Biology Medicine Database, China National Knowledge Infrastructure, China Science and Technology Journal Database, and Wanfang Database were consistently and exhaustively searched. According to the method of evidence-based medicine, the inclusion and exclusion criteria were established, and the meta-analysis of all eligible research results was carried out by using Review Manager 5.3 software. RESULTS: We will disseminate the findings of this systematic review and meta-analysis via publications in peer-reviewed journals. CONCLUSIONS: Our study was carried out to estimate the pooled prevalence of dental caries and its associated factors among Chinese children and adolescents. OSF REGISTRATION NUMBER: DOI 10.17605/OSF.IO/RA9D6.

Flexible Loop in Carbohydrate-Binding Module 48 Allosterically Modulates Substrate Binding of the 1,4-α-Glucan Branching Enzyme.

The 1,4-α-glucan branching enzyme (GBE, EC 2.4.1.18) catalyzes the formation of α-1,6 branching points in starch and plays a key role in synthesis. To obtain mechanistic insights into the catalytic action of the enzyme, we first determined the crystal structure of GBE from Rhodothermus obamensis STB05 (RoGBE) to a resolution of 2.39 Å (PDB ID: 6JOY). The structure consists of three domains: domain A, domain C, and the carbohydrate-binding module 48 (CBM48). An engineered truncated mutant lacking the CBM48 domain (ΔCBM48) showed significantly reduced ligand binding affinity and enzyme activity. Comparison of the structures of RoGBE with other GBEs showed that CBM48 of RoGBE had a longer flexible loop. Truncation of the flexible loops resulted in reduced binding affinity and activity, thereby substantiating the importance of the optimum loop structure for catalysis. In essence, our study shows that CBM48, especially the flexible loop, plays an important role in substrate binding and enzymatic activity of RoGBE. Further, based on the structural analysis, kinetics, and activity assays on wild type and mutants, as well as homology modeling, we proposed a mechanistic model (called the "lid model") to illustrate how the flexible loop triggers substrate binding, ultimately leading to catalysis.

Predicting Apnoeic Events in Preterm Infants.

Apnoea, a pause in respiration, is almost ubiquitous in preterm infants born before completing 30 weeks gestation. Apnoea often begets hypoxemia and/or bradycardia, and has the potential to result in adverse neurodevelopmental consequences. Our current inability to predict apnoeic events in preterm infants requires apnoea to first be detected by monitoring device/s in order to trigger an intervention by bedside (medical or nursing) staff. Such a reactive management approach is laborious, and makes the consequences of apnoeic events inevitable. Recent technological advances and improved signal processing have allowed the possibility of developing prediction models for apnoeic events in preterm infants. However, the development of such models has numerous challenges and is only starting to show potential. This paper identifies requisite components and current gaps in developing prediction models for apnoeic events, and reviews previous studies on predicting apnoeic events in preterm infants.