Xylanase B, a member of subfamily 7 of the GH30 (glycoside hydrolase family 30) from Talaromyces cellulolyticus (TcXyn30B), is a bifunctional enzyme with glucuronoxylanase and xylobiohydrolase activities. In the present study, crystal structures of the native enzyme and the enzyme–product complex of TcXyn30B expressed in Pichia pastoris were determined at resolutions of 1.60 and 1.65 Å, respectively. The enzyme complexed with 2²‐(4‐O‐methyl‐α‐d‐glucuronyl)‐xylobiose (U^4m2X) revealed that TcXyn30B strictly recognizes both the C‐6 carboxyl group and the 4‐O‐methyl group of the 4‐O‐methyl‐α‐d‐glucuronyl side chain by the conserved residues in GH30‐7 endoxylanases. The crystal structure and site‐directed mutagenesis indicated that Asn‐93 on the β2‐α2‐loop interacts with the non‐reducing end of the xylose residue at subsite‐2 and is likely to be involved in xylobiohydrolase activity. These findings provide structural insight into the mechanisms of substrate recognition of GH30‐7 glucuronoxylanase and xylobiohydrolase.

中文翻译：

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纤维素分解双歧杆菌GH30-7木聚糖酶B对底物的识别。

木聚糖酶B是来自解脂Talaromyces cellulolyticus（TC Xyn30B）的GH30（糖苷水解酶家族30）的7亚家族的成员，是一种具有葡糖醛酸木聚糖酶和木糖水解酶活性的双功能酶。在本研究中，在毕赤酵母中表达的天然酶和Tc Xyn30B酶-产物复合物的晶体结构分别以1.60和1.65Å的分辨率测定。该酶与2 ^2-（4 - O-甲基-α - d-葡萄糖醛酸基）木糖（U ^4m2 X）^络合显示Tc Xyn30B严格识别C-6羧基和4- O-甲基4‐GH30-7内切木聚糖酶中保守残基的O-甲基-α - d-葡萄糖醛酸侧链。晶体结构和定点诱变表明，β2-α2环上的Asn-93与亚位点2处木糖残基的非还原端相互作用，并可能参与木糖二糖水解酶的活性。这些发现为GH30-7葡萄糖醛酸木聚糖酶和木糖水解酶的底物识别机制提供了结构上的见识。