摘要
[ Objective ] This study aimed to obtain the recombinant Pichia yeast strain which can efficiently degrade guar gum. The properties of the recombinant enzyme were studied preliminarily. [ Method ] A positive clone that could hydrolyze guar gum was obtained through the construction and functional screening of a soil genome library. Sequence analysis indicated that the 1485-bp clone encodes a 494-amino acid protein with a relative molecular mass of 53 949 kD, containing a cellulose-binding domain. The recombinant plasmid pHBM731 was generated by inserting the optimized target gene into a Pichia pastoris expression vector pHBMg05 that was transformed into three Pichia pastoris strains, GS115, KM71 and SMD1168. The biochemical properties of the enzyme were assessed. [ Result] The cloned galactonumnan （GM）-degrading enzyme was expressed and secreted by Pichia pastoris GSll5. High cell density fermentation was induced in recombi- nant Pichia pastoris at 25 and 28 ~C ; a higher enzyme activity was observed at an induction temperature of 28 ~C. The optimal temperature for the recombinant en- zyme is 60 ~C, and the optimal pH is 6.6. The enzyme activity was 38.61 U under optimal conditions. Over 50% of the enzyme activity was maintained under the optimal conditions after 9 h. Under the optimal conditions, the effect of metal ions on enzyme activity was analyzed. Ca2 ＋ , Fe2 ＋ and Li ~ slightly enhanced enzyme activity, while Mn2＋ and Co2＋ had little effect. Enzyme activity was modestly suppressed by Mg2~ , K~ and Na＋ , but considerably suppressed by Ag2~ and Zn2~ , with Cu2 ＋ showing the strongest inhibitory effects. [ Conclusion] A novel GM-degrading enzyme expressed by soil yeast was cloned, which can potentially be used in industrial applications to obtain eommereially useful guar gum-degradation products.
[ Objective ] This study aimed to obtain the recombinant Pichia yeast strain which can efficiently degrade guar gum. The properties of the recombinant enzyme were studied preliminarily. [ Method ] A positive clone that could hydrolyze guar gum was obtained through the construction and functional screening of a soil genome library. Sequence analysis indicated that the 1485-bp clone encodes a 494-amino acid protein with a relative molecular mass of 53 949 kD, containing a cellulose-binding domain. The recombinant plasmid pHBM731 was generated by inserting the optimized target gene into a Pichia pastoris expression vector pHBMg05 that was transformed into three Pichia pastoris strains, GS115, KM71 and SMD1168. The biochemical properties of the enzyme were assessed. [ Result] The cloned galactonumnan （GM）-degrading enzyme was expressed and secreted by Pichia pastoris GSll5. High cell density fermentation was induced in recombi- nant Pichia pastoris at 25 and 28 ~C ; a higher enzyme activity was observed at an induction temperature of 28 ~C. The optimal temperature for the recombinant en- zyme is 60 ~C, and the optimal pH is 6.6. The enzyme activity was 38.61 U under optimal conditions. Over 50% of the enzyme activity was maintained under the optimal conditions after 9 h. Under the optimal conditions, the effect of metal ions on enzyme activity was analyzed. Ca2 ＋ , Fe2 ＋ and Li ~ slightly enhanced enzyme activity, while Mn2＋ and Co2＋ had little effect. Enzyme activity was modestly suppressed by Mg2~ , K~ and Na＋ , but considerably suppressed by Ag2~ and Zn2~ , with Cu2 ＋ showing the strongest inhibitory effects. [ Conclusion] A novel GM-degrading enzyme expressed by soil yeast was cloned, which can potentially be used in industrial applications to obtain eommereially useful guar gum-degradation products.
基金
Supported by Yantai Municipal Science and Technology Development Plan(2013ZH097)
Scientific and Technological Innovation Fund for Students in Binzhou Medical University(BY2013DKCX122)
