Dror Adi, Shemesh Einav, Dayan Natali, Fishman Ayelet
Department of Biotechnology and Food Engineering, Technion-Israel Institute of Technology, Haifa, Israel.
Appl Environ Microbiol. 2014 Feb;80(4):1515-27. doi: 10.1128/AEM.03371-13. Epub 2013 Dec 20.
The abilities of enzymes to catalyze reactions in nonnatural environments of organic solvents have opened new opportunities for enzyme-based industrial processes. However, the main drawback of such processes is that most enzymes have a limited stability in polar organic solvents. In this study, we employed protein engineering methods to generate a lipase for enhanced stability in methanol, which is important for biodiesel production. Two protein engineering approaches, random mutagenesis (error-prone PCR) and structure-guided consensus, were applied in parallel on an unexplored lipase gene from Geobacillus stearothermophilus T6. A high-throughput colorimetric screening assay was used to evaluate lipase activity after an incubation period in high methanol concentrations. Both protein engineering approaches were successful in producing variants with elevated half-life values in 70% methanol. The best variant of the random mutagenesis library, Q185L, exhibited 23-fold-improved stability, yet its methanolysis activity was decreased by one-half compared to the wild type. The best variant from the consensus library, H86Y/A269T, exhibited 66-fold-improved stability in methanol along with elevated thermostability (+4.3°C) and a 2-fold-higher fatty acid methyl ester yield from soybean oil. Based on in silico modeling, we suggest that the Q185L substitution facilitates a closed lid conformation that limits access for both the methanol and substrate excess into the active site. The enhanced stability of H86Y/A269T was a result of formation of new hydrogen bonds. These improved characteristics make this variant a potential biocatalyst for biodiesel production.
酶在有机溶剂的非天然环境中催化反应的能力为基于酶的工业过程带来了新机遇。然而,此类过程的主要缺点是大多数酶在极性有机溶剂中的稳定性有限。在本研究中,我们采用蛋白质工程方法来生成一种在甲醇中具有更高稳定性的脂肪酶,这对生物柴油生产很重要。两种蛋白质工程方法,即随机诱变(易错PCR)和结构导向的一致性方法,被并行应用于嗜热栖热放线菌T6的一个未探索的脂肪酶基因。在高甲醇浓度下孵育一段时间后,使用高通量比色筛选测定法来评估脂肪酶活性。两种蛋白质工程方法都成功产生了在70%甲醇中半衰期值升高的变体。随机诱变文库的最佳变体Q185L,其稳定性提高了23倍,但其甲醇分解活性与野生型相比降低了一半。一致性文库的最佳变体H86Y/A269T,在甲醇中的稳定性提高了66倍,同时热稳定性提高(+4.3°C),并且从大豆油中产生脂肪酸甲酯的产量提高了2倍。基于计算机模拟,我们认为Q185L取代促进了一种封闭的盖子构象,限制了甲醇和过量底物进入活性位点。H86Y/A269T稳定性的提高是形成新氢键的结果。这些改进的特性使该变体成为生物柴油生产的潜在生物催化剂。