α-环糊精糖基转移酶活性区域突变提高选择形成γ-环糊精能力
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国家自然科学基金 (No. 31171643) 资助。


Increasing of product specificity of γ-cyclodextrin by mutating the active domain of α-cyclodextrin glucanotransferase from Paenibacillus macerans sp. 602-1
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National Natural Science Foundation of China (No. 31171643).

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    摘要:

    探讨α-环糊精糖基转移酶 (CGT酶) 活性区域-3亚位点 (47位赖氨酸残基),-7亚位点 (146~152位氨基酸残基) 以及环化中心位点 (195位酪氨酸残基) 对其催化底物形成γ-环糊精 (CD) 能力的影响。将α-CGT酶相应位点分别进行如下突变:K47T,Y195I,以及146~152位氨基酸残基替换为异亮氨酸 (命名为△6),并在大肠杆菌BL21中实现异源活性表达。以可溶性淀粉作为底物进行转化,利用HPLC分析各种突变酶的催化产物中3种环糊精产量和比例。结果表明,和野生酶相比,所有突变酶的淀粉水解活性和环糊精总生成量都有不同程度的下降。在产物的组成方面,突变酶Y195I的催化产物中,α-CD的含量由68%降为30%,β-CD由22.2%提高为33.3%;而γ-CD由8.9%提高为36.7%,含量提高了4倍,取代α-CD成为产物中的主要成分;γ-CD的实际产量为1.1 g/L,是野生酶 (0.4 g/L) 的3倍。突变酶K47T和△6的转化产物中α-CD比例有不同程度下降,但仍然是产物中的主要组分,β-和γ-CD的比例都有所增加。由此可见,活性区域中195位氨基酸对于α-CGT酶的活力和催化选择性具有重要的影响,Y195I突变体酶最有利于选择性形成γ-CD。纯化后突变酶Y195I的酶学性质试验表明,其最适反应温度和野生酶相同,但最适反应pH有所提高,且比野生酶具有更好的pH稳定性。因此,突变酶Y195I具有生产制备γ-CD的潜力。

    Abstract:

    We studied the mutation effect of subsites -3(Lys47), -7(146-152), and cyclization center (Tyr195) in active domain on product specificity of α-cyclodextrin glucanotransferase (α-CGTase) from Paenibacillus macerans sp. 602-1. The Lys47 was replaced by Thr47 and Tyr195 by Ile195, and the amino acids from 146 to 152 were replaced by Ile (named as Δ6). All these mutant α-CGTases were actively expressed in E. coli BL21. Compared with the wild-type α-CGTase, the starch-degrading activities of all the mutant enzymes were declined. For mutant Y195I, the percentage of α-CD was decreased from 68% to 30%, and β-CD was raised from 22.2% to 33.3%. Interestingly, γ-CD was increased from 8.9% to 36.7% and became the main product, while the actual yield was increased from 0.4 g/L to 1.1 g/L. Mutant K47T and Δ6 still produced α-CD as main product though the percentage of β- and γ-CD increased. Purified Y195I CGTase showed similar optimum temperature with the wild-type α-CGTase, but its optimum pH shifted from 5.0 to 6.0 with better pH stability. In summary, mutant Y195I CGTase has the potential to produce γ-CD as the main product.

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谢婷,岳洋,宋炳红,钞亚鹏,钱世钧. α-环糊精糖基转移酶活性区域突变提高选择形成γ-环糊精能力[J]. 生物工程学报, 2013, 29(9): 1234-1244

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  • 收稿日期:2013-04-21
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  • 在线发布日期: 2013-09-04
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