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Publication Abstract from PubMed

Dextran is an alpha-(1-->6)-glucan that is synthesized by some lactic acid bacteria, and branched dextran with alpha-(1-->2)-, alpha-(1-->3)-, and alpha-(1-->4)-linkages are often produced. Although many dextranases are known to act on the alpha-(1-->6)-linkage of dextran, few studies have functionally analyzed the proteins involved in degrading branched dextran. The mechanism by which bacteria utilize branched dextran is unknown. Earlier, we identified dextranase (FjDex31A) and kojibiose hydrolase (FjGH65A) in the dextran utilization locus (FjDexUL) of a soil Bacteroidota Flavobacterium johnsoniae and hypothesized that FjDexUL is involved in the degradation of alpha-(1-->2)-branched dextran. In this study, we demonstrate that FjDexUL proteins recognize and degrade alpha-(1-->2)- and alpha-(1-->3)-branched dextrans produced by Leuconostoc citreum S-32 (S-32 alpha-glucan). The FjDexUL genes were significantly upregulated when S-32 alpha-glucan was the carbon source compared with alpha-glucooligosaccharides and alpha-glucans, such as linear dextran and branched alpha-glucan from L. citreum S-64. FjDexUL glycoside hydrolases synergistically degraded S-32 alpha-glucan. The crystal structure of FjGH66 shows that some sugar-binding subsites can accommodate alpha-(1-->2)- and alpha-(1-->3)-branches. The structure of FjGH65A in complex with isomaltose supports that FjGH65A acts on alpha-(1-->2)-glucosyl isomaltooligosaccharides. Furthermore, two cell surface sugar-binding proteins (FjDusD and FjDusE) were characterized, and FjDusD showed an affinity for isomaltooligosaccharides and FjDusE for dextran, including linear and branched dextrans. Collectively, FjDexUL proteins are suggested to be involved in the degradation of alpha-(1-->2)- and alpha-(1-->3)-branched dextrans. Our results will be helpful in understanding the bacterial nutrient requirements and symbiotic relationships between bacteria at the molecular level.

Bacteroidota polysaccharide utilization system for branched dextran exopolysaccharides from lactic acid bacteria.,Nakamura S, Kurata R, Tonozuka T, Funane K, Park EY, Miyazaki T J Biol Chem. 2023 Jul;299(7):104885. doi: 10.1016/j.jbc.2023.104885. Epub 2023 , Jun 2. PMID:37269952^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.