Identification and characterization of an endodextranase from <i>Flavobacterium johnsoniae</i> , the first <i>endo</i> -acting enzyme classified within glycoside hydrolase family 27

Glycoside hydrolase family 27 (GH27) consists primarily of exo-acting enzymes, including α-galactosidase, α-N-acetylgalactosaminidase, β-l-arabinopyranosidase, and isomalto-dextranase. Here, we examined the gene expression profiles and biochemical characteristics of a multi-domain protein, Fjoh_4436 (named FjGH27A), which contains a GH27 catalytic domain and is encoded upstream of the previously described branched dextran utilization locus in Flavobacterium johnsoniae. Expression of this gene increased 7.7-fold when cultured with α-(1→2)- and α-(1→3)-branched dextran, produced by Leuconostoc citreum S-32, as the carbon source, compared with cultures using glucose or linear dextran. The catalytic domain of FjGH27A exhibited hydrolytic activity against linear dextran and produced isomaltooligosaccharides of various sizes in an endo-acting manner. The enzyme showed the highest activity toward linear dextran at pH 5.5-6.0 and 25 °C-30 °C. This represents the first identification of an endo-acting enzyme in the GH27 family, offering new insights into the mechanism of branched dextran degradation mediated by FjGH27A.