(S)-酮基布洛芬拆分用脂肪酶基因的克隆及表达

本实验室筛选出一株具有不对称拆分消旋酮基布洛芬氯乙酯的菌株NK13为材料,经鉴定为巨大芽孢杆菌Bacillus megaterium。通过构建其基因文库,从中筛选得到阳性克隆重组子pUC-NK1。测序分析表明,该重组子质粒中包含一长度为633bp的脂肪酶基因的完整开放阅读框,核苷酸同源性对比证明该脂肪酶基因属首次发现(GenBank Accession No.EU381317),将此基因克隆到原核表达载体pET21b(+)中构建重组表达质粒pET-NKest1,转化Escherichia coli BL21,经Isopropyl-β-D-Thiogalactoside(IPTG)诱导在宿主菌中得到表达,经SDS-PAGE电泳检测证明该脂肪酶成熟蛋白分子量约为20kDa。薄层层析与HPLC检测结果显示,表达菌株转化外消旋酮基布洛芬氯乙酯得到(S)-酮基布洛芬过量(e.e.%),由野生菌NK13的5.84%提高到75.28%,提高约15倍,说明该脂肪酶具有优先拆分得到(S)-酮基布洛芬的特性。     

NK13中(S)- 酮基布洛芬拆分用酯酶基因的克隆及表达

以本实验室筛选出的一株具有不对称拆分消旋酮基布洛芬氯乙酯的菌株NK13为材料,经初步鉴定为巨大芽孢杆菌(Bacillus megaterium),通过构建其基因文库,从中筛选得到一阳性克隆重组子pUC-NK。测序分析表明,该重组子质粒中包含一长度为933bp的酯酶基因的完整开放阅读框,核苷酸同源性对比证明该酯酶基因属首次发现（GenBank登录号为DQ196347）,将此基因克隆到原核表达载体pET21b+中构建重组表达质粒pET-NKest,转化E.coli BL21,经IPTG诱导在宿主菌中得到表达,经SDS-PAGE电泳检测证明该酯酶蛋白分子量约为34KDa。薄层层析与HPLC检测结果显示,表达菌株的转化效率较原始菌有明显提高,由表达菌45min就能转化酮基布洛芬氯乙酯47.4％,而得到的(S)-酮基布洛芬过量（e.e.%）由野生菌NK13的5.84％提高到55.46％,提高将近10倍,说明该酯酶具有优先拆分得到(S)-酮基布洛芬的特性。     

利用非经典分泌蛋白质实现脂肪酶A的分泌表达

【目的】以枯草芽孢杆菌脂肪酶A(Lipase A)为报告蛋白,尝试利用4种非经典分泌蛋白质及其前50个氨基酸作为分泌信号以实现其分泌表达。【方法】我们扩增了脂肪酶A的编码基因和非经典分泌蛋白质的编码序列,构建了8种针对脂肪酶A的分泌表达载体,并转化至枯草芽孢杆菌WB800菌株,通过测定重组菌株的酶活、利用蛋白质电泳和免疫印迹等技术检测脂肪酶A的分泌情况【结果】以Pdh A的氨基酸序列和Sod A、Eno的前50氨基酸序列作为分泌信号的重组菌株较好的实现了脂肪酶A的分泌表达。【结论】部分非经分泌蛋白质的编码基因或其前50个氨基酸序列能够引导脂肪酶A分泌至细胞外。     

拆分获得(R)-酮基布洛芬酯酶基因的筛选、克隆与表达

以自筛选出的具有一定不对称拆分外消旋酮基布洛芬氯乙酯能力的野生菌Bacillus megaterium NK13为材料,通过构建其基因文库,筛选得到一个阳性克隆重组子pUC18-NK-HYD3。分析测序结果发现外源片段中包含一段完整的741 bp的开放阅读框,其编码的蛋白中含有酯酶的GXSXG保守序列。经在NCBI的BLAST系统中比对,证明该酯酶基因属于首次发现(GenBank Accession Number: GU143552)。将酯酶基因克隆到载体pET21b(+)中,转化E. coli BL21(DE3),经IPTG诱导后在宿主菌得到表达。SDS-PAGE电泳检测证明该酯酶蛋白分子量约为28 kDa。TLC和HPLC检测结果显示,该酯酶优先水解(R)-型底物,在重组菌菌液体系,转化率为15%时,酯酶拆分获得(R)-酮基布洛芬的过量值(e.e.%)最高,达62.74％;改用重组菌湿菌体的PBS体系后,在转化率为10%~50%时,酯酶拆分获得(R)-酮基布洛芬的过量值(e.e.%)一直保持在73%~76%之间。     

过表达TatAdCd转位酶对枯草芽孢杆菌脂肪酶分泌的影响

【目的】研究过表达枯草芽孢杆菌Tat运输途径的Tat Ad Cd转位酶对促进脂肪酶分泌的影响。【方法】用cdd基因的串联启动子和前导区,替换tat AD-CD操纵子的启动子和前导区,并在染色体sac B基因位点整合表达;采用q RT-PCR方法表征tat AD-CD操纵子的表达水平;用脂肪酶表达质粒p HP13L转化Tat Ad Cd转位酶过表达菌株,构建产脂肪酶重组菌。通过测定脂肪酶活性,以及聚丙烯酰胺凝胶电泳,考察Tat Ad Cd转位酶过表达对脂肪酶分泌的影响。【结果】tat AD-CD操纵子被过表达,其胞内m RNA相对水平提高了185倍。Tat Ad Cd转位酶的过表达,使脂肪酶发酵单位提高了40%。【结论】使用cdd基因的串联启动子和前导区,能够有效地过表达目的基因;枯草芽孢杆菌脂肪酶可以同时经由Sec途径和Tat途径分泌;过表达Tat Ad Cd转位酶,能够显著提高脂肪酶的分泌量。     

绿色荧光蛋白在枯草芽孢杆菌WB600中的表达

根据绿色荧光蛋白(green fluorescent protein,GFP)的特性,将GFP作为目的基因,与穿梭载体p HY300PLK结合,构建一个芽孢杆菌WB600的蛋白表达体系,为在枯草芽孢杆菌中表达其他蛋白提供了一定的技术和理论支持。本文结合p HY300PLK的克隆位点,设计gfp基因的引物,PCR扩增后回收的gfp基因片段进行双酶切,与相同双酶切的pHY300PLK连接获得pHY300PLK-GFP,通过电转化将pHY300PLK-GFP转化至芽孢杆菌WB600中并检测。获得转化子WB1,检测到转化子在荧光显微镜下显示绿色荧光,且后续测序检测表明重组质粒构建成功。     

微生物酶不对称水解合成S(+)-布洛芬的研究 Ⅱ.反应条件和产物提取

皮状丝孢酵母具有较强不对称水解底物专一性.在试验的五种布洛芬消旋酯中,水解甲酯和异丙酯生成s(+)-布洛芬ee可达97%,乙酯为93%以上;而水解活性以乙酯最强,转化率高于30%.不对称水解最适pH6.5—7.0;温度在28—37℃范围内拆分能力无明显差别.该酵母的水解酶为胞内酶,将酵母细胞制成两酮干粉进行水解可提高立体专一性.产物S(+)-布洛芬可借助于酸碱反应和有机溶剂提取得到,同时回收未水解的酯.     

蛋白激发子PeaT1在枯草芽胞杆菌中的分泌表达及重组菌株提高小麦抗旱和促生的作用

PeaT1是从极细链格孢菌Alternaria tenuissima中分离的一种蛋白激发子,具有促进植物生长和诱导植物产生系统获得抗性的功能,为了实现peaT1基因在枯草芽胞杆菌Bacillus subtilis中的分泌表达,增加其应用途径,从枯草芽胞杆菌基因组DNA中分别扩增获得P43启动子和nprB基因的信号肽序列,并用SOE (Splicing by over lapping extension) 方法与peaT1基因连接,将连接产物克隆到大肠杆菌-枯草芽胞杆菌穿梭表达载体pHY300-PLK上,构建了重组表达载体pHY43N-peaT1。将重组载体转化枯草芽胞杆菌WB800菌株,SDS-PAGE和Western blotting分析证实,在NprB信号肽的引导下,枯草芽胞杆菌成功分泌表达了PeaT1蛋白。构建的重组菌株能够显著增强幼苗抗旱性,提高小麦株高。     

信号肽优化在枯草芽孢杆菌体系中对脂肪酶LipS分泌表达的影响

枯草芽孢杆菌具有良好的安全性和优异的外分泌能力,是目前常用的脂肪酶异源分泌表达体系。在枯草体系中如何提高脂肪酶分泌量是目前的研究热点。该体系中信号肽与目的基因不匹配和目标蛋白总表达量不高是导致脂肪酶LipS分泌表达效果较差的重要原因。针对这些问题,依据信号肽结构特征的不同(正电荷与疏水氨基酸个数的差异)对枯草芽孢杆菌体系中Sec和Tat这两个主要分泌途径的信号肽进行了筛选,结果显示Tat途径中的phoD信号肽分泌效果明显优于其他信号肽。在此基础上,通过替换使用诱导型表达载体、突变优化phoD信号肽,并考察了表达条件的影响,显著提高了脂肪酶LipS的分泌表达量,发酵液中转酯酶活达到62.07U/L,占总酶活的62.30%,较原始分泌表达体系的分泌量提高了13.7倍。     

利用枯草芽孢杆菌ytkA和ywoF基因启动子与信号肽重组分泌表达mpd基因

用大肠杆菌-枯草芽孢杆菌穿梭载体pNW33N和去除了信号肽编码序列的成熟mpd基因构建了穿梭启动子探针pNW33N-mpd。用该探针从质粒pMPDP3和pMPDP29上克隆来自于枯草芽孢杆菌ytkA和ywoF基因上游的启动子功能片段,构建了穿梭表达载体pNYTM和pNYWM。将表达载体pNYTM和pNYWM转入枯草芽孢杆菌1A751获得表达菌株1A751(pNYTM)和1A751(pNYTM),mpd基因在ytkA和ywoF基因的启动子和信号肽的带动下实现了分泌表达且具有天然活性,结果表明ytkA基因的启动子强度强于ywoF基因的启动子。利用ytkA基因的强启动子和nprB基因的分泌型信号肽编码序列构建了新的穿梭分泌表达载体pYNMK,并使mpd基因在枯草芽孢杆菌WB800中得到了更高水平的分泌表达,表达菌株WB800(pYNMK)在培养到第84h时甲基对硫磷水解酶酶活达到最高值为10.40u/mL,是出发菌株邻单胞菌M6表达量的10.8倍,重组表达产物有91.4%分泌在培养基中。     

Integration of purification with immobilization of Candida rugosa lipase for kinetic resolution of racemic ketoprofen

The two processes for the partial purification and for the immobilization of a crude lipase preparation (Candida rugosa Lipase OF) have been successfully integrated into one by simple adsorption of the enzyme onto a cation ion exchanger resin (SP-Sephadex C-50) at pH 3.5. Due to selective removal of the unfavorable lipase isoenzyme (L1), the enzyme components (mainly L2 and L3) that are tightly fixed on the resin displayed a significantly improved enantioselectivity (E value: 50 versus 13 with addition of Tween-80) in the biocatalytic hydrolysis of 2-chloroethyl ester of rac-ketoprofen. The activity yields of the immobilized lipase were 48 and 70%, respectively when emulsified and non-emulsified substrates were employed for enzyme assay. Moreover, the concentration of Tween-80 was found to be a factor affecting the lipase enantioselectivity. By using such an immobilized enzyme as biocatalyst, the process for preparing enantiopure (S)-ketoprofen becomes simpler and more practical as compared with the previously reported procedures and the product was obtained with >94% ee at 22.3% conversion in the presence of an optimal concentration (0.5 mg/ml) of Tween-80 at pH 3.5. Furthermore, the operational stability of the immobilized biocatalyst was examined in different types of reactors. In an air-bubbled column reactor, the productivity was much higher than that in a packed-bed column reactor, in spite of a slightly lower stability. Under optimal conditions, the air-bubbled column reactor could be operated smoothly for at least 350 h, remaining nearly 50% activity.     

Molecular cloning and functional expression of a novel extracellular lipase from the thermotolerant yeast Candida thermophila

The thermotolerant yeast Candida thermophila SRY-09 isolated from Thailand produces an extracellular lipase that hydrolyses various triglycerides. To clone the gene encoding the lipase, Saccharomyces cerevisiae was transformed with a C. thermophila genomic library and screened for lipase activity on medium containing olive oil emulsion and rhodamine B. One C. thermophila lipase gene (CtLIP) was found that contained an ORF of 1317 bp encoding a deduced polypeptide of 438 amino acids. Candida thermophila lipase contained a Gly-Asp-Ser-Gln-Gly motif which matched the consensus Gly-X-Ser-X-Gly conserved among lipolytic enzymes. Heterologous expression of the cloned CtLIP under the control of the alcohol oxidase gene (AOX1) promoter in the methylotrophic yeast Pichia pastoris, and enzymatic measurements confirmed the function of the respective protein as a lipase. The recombinant CtLIP could hydrolyse various substrates at high temperature (55 degrees C) with higher efficiency than at 37 or 45 degrees C and preferentially hydrolysed two-positional ester bonds. As with C. thermophila, the heterologously expressed lipase was secreted into the medium by Pichia pastoris.     

Screening and its potential application of lipolytic activity from a marine environment: characterization of a novel esterase from <Emphasis Type="Italic">Yarrowia lipolytica</Emphasis> CL180

To develop an enantioselective lipase/esterase hydrolyzing racemic ofloxacin ester to levofloxacin, samples were collected from a variety of marine environments such as cold sea, hydrothermal vent area, sediment, tidal flat area, arctic sea, marine organisms, and so on. Microorganisms were isolated by plating on an enrichment medium with simultaneous detection of lipolytic activities and screened for the hydrolysis of ofloxacin ester. Three candidates among isolates were selected, and one of them, identified as Yarrowia lipolytica CL180, hydrolyzed preferentially S-enantiomer of racemic ofloxacin ester. The lipase/esterase gene (yli180) was cloned by screening a genomic library. The sequence analysis revealed an open reading frame consisting of 1,431 bp that encoded a protein of 476 amino acids with a molecular mass of 53 kDa. The yli180 gene was expressed in Escherichia coli and purified to homogeneity. The optimum activity of the recombinant protein (rYli180) occurred at pH 7.5 and 35°C, respectively. rYli180 preferentially hydrolyzed p-nitrophenyl esters of fatty acids with short chain lengths of ≤10 carbon atoms. This study represents a novel esterase of type B1 carboxylesterase/lipase family from a marine isolate, showing a potential usage as a biocatalyst because of enantioselectivity toward racemic ofloxacin ester.     

Construction and characterization of a recombinant esterase with high activity and enantioselectivity to (S)-ketoprofen ethyl ester

The ester-hydrolyzing enzyme families, including lipase and esterase, mediated a broad range of reactions and, thus, were able to act on a variety of ester compounds that are found naturally or exploited industrially. With the increasing demand for pharmacological use, attempts to produce an enantiomer (S)-ketoprofen from the corresponding ethyl ester have recently been proliferating, but information about the structure and function of related enzymes has not been reported to date in detail. Here, we reported the construction, expression, and one-step purification of a potential esterase in Escherichia coli with a hexahistidine tag at its N-terminus. The expression level of the enzyme was more than 20% of the total protein in E. coli, resulting in approximately 1.2mg of the purified proteins by an affinity resin, Ni-NTA, from a 0.2L of bacterial culture in a single step. As typical properties, its innate traits that revealed favorable reactions at alkaline pH and high activity to the triglycerides composed of short chain fatty acids (99% ee(p)). The small-scale conversion using the recombinant enzyme strongly suggested the enzyme to be useful for enzyme-mediated chiral resolution of (S)-ketoprofen.     

牦牛瘤胃中产脂肪酶微生物的分离与鉴定

【背景】脂肪酶是一类特殊的酯键水解酶,广泛应用于工业化生产中,微生物是工业脂肪酶的主要来源。瘤胃中微生物种类繁多、数量庞大,已有关于瘤胃微生物产纤维素酶的报道,尚无产脂肪酶瘤胃微生物的分离筛选报道。【目的】从牦牛瘤胃中分离筛选出能够产脂肪酶的微生物,并进行菌株鉴定及其酶学性质的研究。【方法】以橄榄油为唯一碳源,通过中性红油脂平板进行初步筛选后,用改进铜皂-分光光度法测定酶活力进行复筛;再经形态学观察、生理生化实验和16S rRNA基因序列分析进行菌种鉴定;研究3种脂肪酶的最适作用温度、pH值及金属离子、有机溶剂和表面活性剂对酶活力的影响。【结果】筛选出6株酶活力较高的菌株,其中3株为液化沙雷氏菌,2株为白地霉,1株为卷枝毛霉。脂肪酶的酶学性质研究表明:液化沙雷氏菌、白地霉和卷枝毛霉所产脂肪酶的最适作用温度为45、35和40°C;最适pH为8.0、7.0和7.0;Ca2+和Mg2+对3种脂肪酶均有激活作用;Zn2+对3种脂肪酶有不同程度的抑制作用,EDTA、SDS可使3种脂肪酶失活;3种脂肪酶对丙三醇的耐受力较高,卷枝毛霉脂肪酶对甲醇、乙醇、丙酮的耐受力较高。【结论】从牦牛瘤胃中分离出3种产脂肪酶的微生物,且证实瘤胃微生物在脂肪酶研究方面具有较高的价值。     

Hydrolysis of triacylglycerol arachidonic and linoleic acid ester bonds by human pancreatic lipase and carboxyl ester lipase

The hydrolysis of polyenoic fatty acid ester bonds with pure human colipase-dependent lipase, with carboxyl ester lipase (CEL) and with these enzymes in combination was studied, using [3H]arachidonic- and [14C]linoleic acid-labelled rat chylomicrons as a model substrate. During the hydrolysis with colipase-dependent lipase, the amount of 3H appearing in 1,2-X-diacylglycerol (DG) markedly exceeded that of 14C. When CEL was added in addition this [3H]DG was efficiently hydrolyzed. CEL alone hydrolyzed the triacylglycerol (TG) at a low rate. The hydrolysis pattern with human duodenal content was similar to that seen with colipase-dependent lipase and CEL in combination. Increasing the concentration of taurodeoxycholate (TDC) and taurocholate (TC) or of TDC alone stimulated the hydrolysis of [3H]- and [14C]TG, but increased the accumulation of labelled DG that could act as substrate for CEL. It is suggested that very-long-chain polyenoic fatty acids of DG formed during the action of the colipase-dependent lipase on TG containing these fatty acids may be a physiological substrate for CEL.     

Carboxyl ester lipase cofractionates with scavenger receptor BI in hepatocyte lipid rafts and enhances selective uptake and hydrolysis of cholesteryl esters from HDL3

Cholesteryl esters are selectively removed from high density lipoproteins by hepatocytes and steroidogenic cells through a process mediated by scavenger receptor BI. In the liver this cholesterol is secreted into bile, primarily as free cholesterol. Previous work showed that carboxyl ester lipase enhanced selective uptake of cholesteryl ether from high density lipoprotein by an unknown mechanism. Experiments were performed to determine whether carboxyl ester lipase plays a role in scavenger receptor BI-mediated selective uptake. When added to cultures of HepG2 cells, carboxyl ester lipase cofractionated with scavenger receptor BI and [(3)H]cholesteryl ether-labeled high density lipoprotein in lipid raft fractions of cell homogenates. Confocal microscopy of immunostained carboxyl ester lipase and scavenger receptor BI showed a close association of these proteins in HepG2 cells. The enzyme and receptor also cofractionated from homogenates of mouse liver using two different fractionation methods. Antibodies that block scavenger receptor BI function prevented carboxyl ester lipase stimulation of selective uptake in primary hepatocytes from carboxyl ester lipase knockout mice. Heparin blockage of cell-surface proteoglycans also prevented carboxyl ester lipase stimulation of cholesteryl ester uptake by HepG2 cells. Inhibition of carboxyl ester lipase activity in HepG2 cells reduced hydrolysis of high density lipoprotein-cholesteryl esters approximately 40%. In vivo, hydrolysis was similarly reduced in lipid rafts from the livers of carboxyl ester lipase-null mice compared with control animals. Primary hepatocytes from these mice yielded similar results. The data suggest that carboxyl ester lipase plays a physiological role in hepatic selective uptake and metabolism of high density lipoprotein cholesteryl esters by direct and indirect interactions with the scavenger receptor BI pathway.