Panpan Zhang,Jinhui Jia,Pingrui Jiang,Weiyun Zheng,Xiangfei Li,Shuang Song,Chunqing Ai
Brown seaweed is rich in polysaccharides including sulfated polysaccharides and alginate, both of which provide health benefits to the host but whose differences have not received sufficient attention. In this study, alginate from Undaria pinnatifida (UPA) and sulfated polysaccharides from U. pinnatifida (UPSP) were isolated, and their action was analyzed in high fat diet-fed mice. UPA and UPSP improved body composition, fat deposition in body tissues and organs, lipid abnormality and inflammatory response in mice, and compound polysaccharides from U. pinnatifida (UPP: UPA + UPSP) had a better effect on some physiological indexes, which could be attributed to the differences in the gut microbiota. Both UPSP and UPA modulated diet-induced microbiota dysbiosis, and UPP had better effect on changes in the gut microbiota, including an increase in Bacteroidales and reduction in both Clostridiales and Lactobacillales that had positive correlations with the improvement of the physiological status. The in vitro model of bacterial culture revealed that the use of Bacteroides on UPA and UPSP was species dependent, and UPP can better maintain the diversity and stability of the Bacteroidales community. This study indicated that polysaccharides from edible brown seaweed can benefit host health by improving the intestinal microecology, which can be helpful for the application of edible brown seaweed in health foods.
Alginate is a commercially important polysaccharide widely distributed in brown algae. Carbohydrate-binding modules (CBMs), a class of commonly used polysaccharide-binding proteins, have greatly facilitated the investigations of polysaccharides. Few alginate-binding CBMs have been hitherto reported and structurally characterized. Herein, an unknown domain from a potential PL6 family alginate lyase in the marine bacterium Vibrio breoganii was discovered and recombinantly expressed. The obtained protein, designated VbCBMxx, displayed the favorable specificity to alginate. The unique sequence and well-defined function of VbCBMxx reveal a new CBM family. Moreover, the structure of VbCBMxx was determined at a 1.5 Å resolution by the X-ray crystallography, which shows a typical β-sandwich fold comprised of two antiparallel β-sheets. Site-directed mutagenesis assays confirmed that positively charged polar residues are crucial for the ligand binding of VbCBMxx. The discovery of VbCBMxx enriches the toolbox of alginate-binding proteins, and the elucidation of critical residues would guide the future practical applications of VbCBMxx.
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