Codon optimization, expression and enzymatic comparison of Rhizopus oryzae lipases pro-ROL and m-ROL in Pichia pastoris / 生物工程学报

Rhizopus oryzae lipase (ROL) is not only a biocatalyst used in a broad range of biotechnological fields, but also a model to investigate the function of intramolecular chaperone in the post-translational processing of lipase. In this study, we cloned and expressed the mature lipase gene (m-ROL) containing the pre-sequence (pro-ROL) of R. oryzae HU3005 in Pichia pastoris GS115 and characterized their enzymatic activities. m-ROL exhibited higher hydrolysis activity towards middle-chain substrates (C10 and C12) at pH 9.0, whereas pro-ROL preferred short-chain substrates (C4) and displayed maximal activity at pH 8.0. Moreover, pro-ROL possessed better thermal stability than m-ROL. This enzymatic discrepancy between m-ROL and p-ROL may be due to the pre-sequence that affects the folding and conformation of the mature lipase domain. To improve the expression level of m-ROL in P. pastoris, overlap extension PCR was conducted to substitute eight less-frequently used codons of m-ROL with frequently used codons. After methanol-induced expression for 72 h, the activity and protein content of the codon optimized m-ROL reached 132.7 U/mL and 50.4 mg/L, while the activity of the parental m-ROL and pro-ROL are 28.7 U/mL and 14.4 mg/L, 29.6 U/mL and 14.1 mg/L, respectively.

Homologous expression of Burkholderia cepacia G63 lipase gene based on T7 RNA polymerase expression system / 生物工程学报

In order to realize over-expression of Burkholderia cepacia (B. cepacia) lipase, we introduced the widely used T7 RAN polymerase expression system into B. cepacia G63 to over-express the lipase gene. By using PCR technique, we amplified the T7 RNA polymerase gene (T7 RNAP) from the BL21 (DE3) and cloned it into the suicide plasmid pJQ200SK. After that, we flanked T7 RNAP with two 500 bp homologous fragments and integrated it into the genomes of B. cepacia by tri-parental mating, so that T7 RNAP was under-controlled by lipase gene (lipA) promoter. Then, we cloned the lipA and its partner gene lipB into the vector pUCPCM and pBBR22b both or separately. Therefore, we got 7 expression plasmids pBBR22blipAB, pBBR22blipA, pUCPCMlipAB, pUCPCMlipA, pUCPCMdeltalipAlipB, pUCPCMdeltalipA, pUCPCMdeltalipB, and then electroporated them into B. cepacia containing T7 RNA. After shake flask culture, we found B. cepacia containing pUCPCMlipAB produced the most quantity of lipase, and lipase activity was up to 607.2 U/mg, 2.8-folds higher than that of the wild strain. Moreover, lipase activities of all engineering strains except the one containing pUCPCMdeltalipB were enhanced to some extent. The specific activities of wild type B. cepacia and B. cepacia containing pUCPCMlipAB were respectively 29 984 U/mg and 30 875 U/mg after ammonium sulfate precipitation and gel filtration chromatography. The T7 RNA polymerase expression system could effectively enhanced lipase expression in B. cepacia, and secretion signal PelB and ribosome-binding site may promote lipase expression in engineering strain.

Two-step synthesis of the full length Aspergillus niger lipase gene lipA leads to high-level expression in Pichia pastoris / 生物工程学报

Aspergillus niger lipases are important biocatalysis widely used in industries for food processing and pharmaceutical preparation. High-level expression recombinants can lead to cost effective lipase large scale production. Full length gene synthesis is an efficient measure to enhance the expression level of the gene. In order to reduce the non-specific binding between oligonucleotides and bases mutation caused by the complicate secondary structure of DNA and excessive PCR amplification, a frequently phenomenon in one-step gene synthesis, we used a two-step method including assembly PCR (A-PCR) and digestion-ligation step to synthesis Aspergillus niger lipase gene lipA. Assisted by DNA2.0 and Gene2Oliga software, we optimized the codon usage and secondary structure of RNA and induced enzyme sites Cla I (237 site) and Pst I (475 site) into the gene. In the first step, fragments F1 (237 bp), F2 (238 bp) and F3 (422 bp) were separately synthesized by assembly PCR. In the second step, fragments F1, F2 and F3 were separately digested by Cla I and Pst I, and then ligated into a full length lipA gene. Two-step method efficiently enhanced successful ratio for full-length gene synthesis and dispersed the risk for gene redesign. The synthesized gene was cloned into pPIC9K vector and transferred into Pichia pastoris. After methanol inducement, the expression level of the codon optimized lipA-syn gene reached 176.0 U/mL, 10.8-fold of the original lipA gene (16.3 U/mL) in Pichia pastoris GS1115. The recombinant offers the possibility for lipase large-scale production.

Directed evolution of lipase of Bacillus pumilus YZ02 by error-prone PCR / 生物工程学报

Random mutagenesis on Bacillus pumilus lipase YZ02 gene was conducted by using error-prone PCR strategy. Through two cycles of directed evolution, two optimum mutants BpL1-7 and BpL2-1369 with lipase activity improved 2 folds and 6 folds respectively were screened. The sequence of BpL2-1369 lipase gene showed that four nucleotides substitution, T61C, C147T, A334G and T371A have occurred, and three of them caused amino acid changes. Thus, amine acid Ser21 was changed into Pro21, Arg112 to Gly112, and Leu124 to His124. According to the 3D structure of Bacillus pumilus lipase mimicked by SWISS-MODEL Repository, three mutated amino acids were located at the third amino acid of the first alpha-helix, the turn between the fourth and fifth beta fold, and the first amino acid of the fifth beta fold, respectively. The BpL and BpL2-1369 genes were ligated into pET28a vector, and transferred into E. coli BL21 (DE3). After induced by IPTG the lipases were purified and characterized. The results showed that the specific activity of the evolved lipase was 1.31-fold than that of the wild lipase, and the Km decreased from 8.24 mmol/L to 7.17 mmol/L. The pH stability of the evolved lipase was better than wild lipase when pH>8.0.