宏基因组来源嗜热β-木糖苷酶XlyY411的酶学性质研究

Biochemical characterization of a thermophilic β-xylosidase XlyY411 from a hot spring metagenome

  • 摘要: 从云南省元江县热水塘温泉的宏基因组中挖掘到编码糖苷水解酶39家族 (GH39) 的β-木糖苷酶基因xlyY411. 将该基因在Escherichia coli BL21进行异源表达,通过亲和层析获得较纯的重组酶XlyY411. 该酶的最适温度为85 ℃,90 ℃时的t1/2为6.2 h. 最适pH为5.0,4 ℃时,在pH = 5~9之间有较好的pH耐受性. XlyY411在添加10%的β-巯基乙醇或吐温的应用体系中,相对酶活保持在75%以上,表明其对表面活性剂有较好的耐受性. 在20%的甲醇、乙醇或异丙醇体系中,相对酶活大于50%,表明其对有机溶剂有较好的耐受性. 在2 mmol/L的木糖浓度下相对酶活为51.6%,表现出较好的产物耐受性. 酶促动力学研究表明,XlyY411的KM为(7.19±0.89) mmol,vmax4753.68 mmol/(mg·min),kcat为223.91 s,kcat/KM为31.14 s−1 ∙mmol−1. 分子对接分析表明XlyY411与已报道的GH39家族β-木糖苷酶具有相似的催化机制.

     

    Abstract: In this study, the β-xylosidase gene xlyY411, belonging to glycoside hydrolase family 39 (GH39), was mined from the metagenome of a hot spring in Yuanjiang County, Yunnan Province, China. The gene was heterologously expressed in Escherichia coli BL21 and purer recombinant enzyme XlyY411 was obtained by affinity chromatography. The optimum temperature of XlyY411 was 85 ℃, and the t1/2 at 90 ℃ was 6.2 h. The optimum pH was 5.0, and there was a good pH tolerance between pH 5−9 at 4 ℃. XlyY411 displayed a good tolerance to surfactants, while its activity of was above 75% with the addition of 10% β-mercaptoethanol or tween; XlyY411 displayed a good tolerance to organic solvents, while its activity of was above 50% with the addition of 20% methanol, ethanol or isopropanol; There was 51.6% enzyme activity at a xylose concentration of 2 mmol/L, showing its good product tolerance. Enzymatic kinetic studies showed that XlyY411 had a KM of (7.19 ± 0.89) mmol, a vmax of 4753.68 mmol/(mg·min), a kcat of 223.91 s, and a kcat/KM of 31.14 s−1·mmol−1. The molecular docking analysis indicate that XlyY411 had similar catalytic mechanism to the β-xylosidases reported in literature.

     

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