湖羊瘤胃微生物GH9家族葡聚糖酶基因IDSGLUC9-25的表达与功能表征

【目的】葡聚糖酶是饲用添加剂的重要成分,本研究旨在从湖羊消化道微生物中挖掘性质优良的GH9家族葡聚糖酶基因,用于研发新型饲用酶制剂。【方法】从湖羊瘤胃微生物cDNA中扩增IDSGLUC9-25基因,在大肠杆菌中进行异源表达,对重组蛋白进行诱导表达和纯化,研究重组蛋白的酶学性质和底物水解模式。【结果】IDSGLUC9-25基因编码527个氨基酸,包含一个CelD_N结构和一个GH9家族催化结构域;重组蛋白rIDSGLUC9-25分子量约为62.7 kDa,最适反应温度和pH分别为40℃和6.0,在30-50℃下活性较高,在pH 4.0-8.0范围内能够保持较高的稳定性,经pH 4.0-8.0缓冲液处理1 h后残余活性均大于90%;底物谱分析表明,rIDSGLUC9-25能催化大麦β-葡聚糖、苔藓地衣多糖、魔芋胶和木葡聚糖,比活性分别为(443.55±24.48)、(65.56±5.98)、(122.37±2.85)和(159.16±7.73) U/mg;利用薄层色谱法(thin layer chromatography, TLC)和高效液相色谱法(high performance liquid chromatography, HPLC)分析水解产物发现,rIDSGLUC9-25降解大麦葡聚糖主要生成纤维三糖(占总还原糖64.19%±1.19%)和纤维四糖(占总还原糖26.24%±0.12%),催化地衣多糖主要生成纤维三糖(占总还原糖78.46%±0.89%)。【结论】本研究报道了一种来自密螺旋体属细菌的内切β-1,4-葡聚糖酶IDSGLUC9-25 (EC 3.2.1.4),能高效催化多糖底物生成纤维三糖和纤维四糖,为研发饲用酶制剂和制备低聚寡糖建立基础。

Heterologous expression and characterization of a GH9 glucanase gene IDSGLUC9-25 from rumen microbiota in Hu sheep

【Objective】 Glucanases serve as one of the main components in feed additives. This study identified and characterized a novel GH9 glucanase gene derived from rumen microbiota in herbivores, aiming to provide a reference for the research and development of feed enzymes. 【Methods】 We obtained the IDSGLUC9-25 gene from the rumen fluid cDNA of Hu sheep and heterologously expressed it in Escherichia coli. The recombinant protein was induced for expression by isopropyl β-D-thiogalactopyranoside, purified, and then subjected to functional characterization. 【Results】 IDSGLUC9-25 encoded a protein consisting of 527 amino acid residues, which included a CelD_N domain and a GH9 family catalytic domain. The recombinant rIDSGLUC9-25 protein exhibited a molecular weight of approximately 62.7 kDa and the highest enzymatic activity at 40 °C and pH 6.0. The enzyme displayed robust catalytic activity within the temperature range of 30–50 °C. After preincubation at pH 4.0–8.0 for 1 h, rIDSGLUC9-25 retained the relative activity over 90%. The substrate spectrum analysis revealed that rIDSGLUC9-25 exhibited specific activities against barley β-glucan, moss lichenan, konjac gum, and xyloglucan, with the activities of (443.55±24.48), (65.56±5.98), (122.37±2.85), and (159.16±7.73) U/mg, respectively. The hydrolysis assay showed that rIDSGLUC9-25 primarily catalyzed the hydrolysis of β-glucan into cellotriose (representing 64.19%±1.19% of total reducing sugars) and cellotetraose (representing 26.24%±0.12% of total reducing sugars). Additionally, the enzyme predominantly generated cellotriose from the hydrolysis of lichenan (representing 78.46%±0.89% of total reducing sugars). 【Conclusion】 This study characterizes IDSGLUC9-25, an endo-β-1,4-glucanase (EC 3.2.1.4) derived from Treponema sp. The enzyme exhibited robust activity in the conversion of polysaccharides into cellotriose and cellotetraose, establishing a foundation for the development of feed enzymes and functional oligosaccharides preparation.