Rhizopus oryzae lipase (ROL) is important because of its extreme sn-1,3-regioselectivity, but it shows poor thermostability, which severely restricts its application. In this work, the thermostability of ROL was greatly enhanced by rational design. First, several sites that may affect the thermostability of ROL were identified by multiple-sequence alignment. The half-lives of mutants V209L and D262G at 55 °C were about 4.38- and 4.2-times those of the wild-type, respectively. Then, a disulfide bond was introduced between positions 190 and 238 based on the prediction of Disulfide by Design 2, which greatly improved the thermostability of the protein. The activity of variant E190C/E238C retained about 58.2% after incubation at 55 °C for 720 min, whereas the half-life of wild type ROL was only about 11.7 min. On the basis of the results obtained by the two methods, we carried out a combined mutation. Quadruple mutant V209L/D262G/E190C/E238C was constructed and the thermostability was improved even further. The half-lives at 55 °C and 65 °C were 102.5- and 20-times those of the wild-type ROL. This improvement in thermostability will give ROL wider industrial applicability, especially in the preparation of structured lipids.
Lili Xu,Qingqing Zhao,Haibo Liu,Dankui Liao,Aixing Tang,Youyan Liu
Limonene dioxide (LDO) is essential for manufacturing bio-based polycarbonate and non-isocyanate polyurethanes. Herein, we report a strategy for the chemoenzymatic epoxidation of (R)-(+)-limonene to LDO with high selectivity using Rhizopus oryzae whole cells. The presence of sufficient excess acid in the system is essential, in addition to overcoming the hydrolysis of the intermediate product, 1,2-limonene oxide, to accomplish the double epoxidation of limonene. When using a high concentration of H 2 O 2 and trisodium citrate, the conditions were effectively established, even when Novozym 435 was substituted, which had previously been reported to be ineffective in achieving high-yield double epoxidation of limonene. The transfer of H 2 O 2 and peracids between the cell and solvent slowed production. The total amount of peracids generated remained constant, but their concentrations remained moderate, favoring the double epoxidation of limonene. An LDO yield of 93 % and no intermediate product, limonene oxide, were obtained under optimized conditions within 20 h.
Nano-sized Fe 3 O 4 was synthesized by chemical co-precipitation and subsequently modified with 3-aminopropyltriethoxysilane (APTES) and glutaraldehyde to introduce aldehyde group on its surface. With the help of “interface activation” by adding sucrose esters-11 as surfactant, lipase from Rhizopus oryzae was successfully immobilized onto the carrier with great enhancement of activity. The hydrolysis activity of immobilized enzyme were 9.16 times and 31.6 times of free enzyme when p-nitrophenol butyrate and p-nitrophenol palmitate were used as substrates. The thermo-stability of immobilized enzyme was also enhanced compared to free enzyme. The immobilized enzyme was successfully applied in synthesis of 1,3-diacyglycerols (1,3-DAG). The specific esterification activity of immobilized enzyme was about 1.5 times of the free enzyme. The immobilized enzyme showed good region-selectivity towards 1,3-diacyglycerols and retained nearly 80% of its activity after reused for 60 times, revealing a good industrial application prospect.
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