耐碱性甘露聚糖酶基因的克隆及其在毕赤酵母中的表达

通过功能平板从土壤中筛选得到含甘露聚糖酶基因的耐碱菌株。构建其基因组文库,从中筛选到甘露聚糖酶基因TM1并测序分析,用BLAST分析表明,TM1的氨基酸序列与其他在GenBank发表的甘露聚糖酶的氨基酸序列的同源性均低于60%,故确定其为一个新的甘露聚糖酶基因(GenBank登录号为AY623903)。将此基因去除信号肽后的编码序列克隆到表达载体pHBM905C上,得到重组质粒pHBM1201。经SalⅠ酶切后分别转化毕赤酵母(Pichiapastoris)KM71、GS115、SMD1168,得到分泌表达的重组毕赤酵母。挑选相对表达量最高的重组毕赤酵母SMD1168-3在摇瓶中诱导产酶,对该酶的粗酶进行酶学性质分析表明,其最适反应温度为55℃,最适PH值为7.5,以魔芋粉为底物所测得的最高酶活为41.8U,半衰期为1h,在80℃保温5min其酶活由最初酶活的77%下降到11%,温度下降到55℃后活性可恢复到最初酶活的60%以上。

Cloning and expression in Pichia pastoris of an alkaline mannanase gene

A strain containing alkaline mannanase gene was isolated from soil by functional plates and the genome library was constructed. From it a mannanase gene TM1 was acquired and was sequenced. The BLAST analysis showed a lower-than-60% similarity of the amino acid sequence to those in GenBank and proved TM1 to be a new mannanase gene (GenBank accession number AY623903). The new gene without signal peptide was cloned into the Pichia pastoris expression vector pHBM905C. The recombinant plasmid pHBM1201 was digested by Sal I and transformed into Pichia pastoris KM71, GS115, SMD1168, respectively. All of the recombinant Pichia pastroris strains containing pHBM1201 secreted functional beta-mannanase. Because of its high mass of expression, the recombinant Pichia pastoris SMD1168-3 containing pHBM1201 was induced at shake flasks. The optimal temperature and pH of the beta-mannanase produced by the recombinant strains were 55 degrees C and 7.5, respectively. The enzymatic activity for konjak powder reached 41.8 with a half life of one hour. After keeping at 80 degrees C for 5 min, the enzymatic activity declined from 77% to 11% and the enzymatic activity could recover up to more than 60% when the temperature descended to 55 degrees C.