硫色曲霉木聚糖酶基因xynA与xynB在大肠杆菌中的融合表达及酶学性质分析

In-fusion Expression of Xylanase Genes XynA and XynB From Aspergillus sulphureus in E. coli and Characterization of The Recombinant Enzyme

根据硫色曲霉木聚糖酶基因xynA和xynB序列设计引物,PCR扩增获得574bp、594bp的目的基因片段.两段DNA分别用EcoRⅠ/BamHⅠ、BglⅡ/HindⅢ酶切后,连接到载体pET-28a(+)的多克隆位点,构建了xynA和xynB融合表达载体pET-xynAB,即在木聚糖酶A和B之间引入了7个氨基酸的寡肽序列(GlyGlyGlySerGlyGlyGly).将pET-xynAB转化大肠杆菌BL21,经IPTG诱导,SDS-PAGE检测到了一条约50ku的特异性表达条带.Ni-NTA柱纯化后的特异性蛋白经8mol/L脲素变性,梯度透析使蛋白质复性.酶学性质分析表明,该重组木聚糖酶的最适催化温度为50℃,最适pH值为4.4.在pH2.4～5.4范围内,酶的相对活性都在75%以上,重组酶在80℃保温30min还有近50%的残余酶活.不同种类的金属离子对重组酶的活力影响不同.

Two sets of primers were designed according to the sequences of xynA and xynB from Aspergillus sulphureus, and the DNA fragments composed of 574 bp and 594 bp were amplified by polymerase chain reaction （PCR）, respectively. The two PCR products respectively digested with EcoR Ⅰ/BamHⅠ and BgⅢ/Hind In were ligated into multiple cloning sites ofpET-28a（＋）. The resulting plasmid is pET-xynAB, in which xylanase A and B are ligated by a 7-amino acid peptide （GlyGlyGlySerGlyGlyGly）. E. coli BL21 transformed with pET-xynAB was induced by IPTG, and a special protein band about 50 ku was detected by SDS-PAGE. The protein purified with Ni-NTA column was denatured by 8 mol/L urea and dialyzed for refolding. The recombinant xylanase showed optimal activity at 50℃ and pH 4.4. The enzyme retained above 75% of its activity at the range ofpH 2.4-5.4. The xylanase displayed about 50% retained acitivity after incubating at 80℃ for 30 min. Various metal ions have different effects on activity of the recombinant xylanase.