Glycoside hydrolase family (GH) 31 contains a large variety of enzymes, but the major members are enzymes that act on relatively small oligosaccharides such as α-glucosidase. Here, we determined the crystal structure of Flavobacterium johnsoniae dextranase (FjDex31A), an enzyme from F. johnsoniae that hydrolyzes a polysaccharide, dextran. FjDex31A is composed of four domains: an N-terminal domain, a catalytic domain, a proximal C-terminal domain, and a distal C-terminal domain, as observed in typical GH31 enzymes. However, the architecture of active site residues in FjDex31A, other than subsite -1, is markedly different from that of other GH31 enzymes. The FjDex31A structure in complex with isomaltotriose shows that Gly273 and Tyr524, both of which interact with an α-glucose residue at subsite -2, as well as Trp376 and Leu308-cisGln309, are especially unique to FjDex31A. Site-directed mutagenesis of Gly273 and Tyr524 resulted in a decrease in the hydrolysis of polysaccharides dextran and pullulan, as well as that of the disaccharide isomaltose. These results suggest that, regardless of the length of sugar chains of the substrates, binding of FjDex31A to the substrates at subsite -2 is likely to be important for its activity. DATABASE: Structural data are available in the Protein Data Bank under the accession numbers 6JR6, 6JR7, and 6JR8.

中文翻译：

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约翰逊黄杆菌葡聚糖酶（一种糖苷水解酶家族31的成员）对多糖识别的结构见解。

糖苷水解酶家族（GH）31包含多种酶，但主要成员是作用于相对较小的寡糖的酶，例如α-葡萄糖苷酶。在这里，我们确定了约翰逊黄杆菌葡聚糖酶（FjDex31A）的晶体结构，该酶来自约翰逊F.水解多糖葡聚糖。FjDex31A由四个域组成：N末端域，催化域，近端C端域和远端C端域，如在典型的GH31酶中所观察到的。但是，FjDex31A中除亚位点-1之外的活性位点残基的结构与其他GH31酶明显不同。与异麦芽三糖复合的FjDex31A结构表明，Gly273和Tyr524都与亚位点-2处的α-葡萄糖残基以及Trp376和Leu308-cisGln309相互作用，对于FjDex31A尤其独特。Gly273和Tyr524的定点诱变导致多糖葡聚糖和支链淀粉以及二糖异麦芽糖的水解减少。这些结果表明，不管底物的糖链的长度如何，FjDex31A在位点-2处与底物的结合可能对其活性很重要。数据库：结构数据可从蛋白质数据库中获得，登录号为6JR6、6JR7和6JR8。FjDex31A与亚位点-2底物的结合可能对其活性很重要。数据库：结构数据可从蛋白质数据库中获得，登录号为6JR6、6JR7和6JR8。FjDex31A与亚位点-2底物的结合可能对其活性很重要。数据库：结构数据可从蛋白质数据库中获得，登录号为6JR6、6JR7和6JR8。