凝胶色谱柱复性在低分子量尿激酶原突变体(DscuPA\|32K)中的应用

将构建的一种具溶栓和抗栓双重功能尿激酶原突变体(DscuPA\|32K)基因,在大肠杆菌中进行表达。由于DscuPA\|32K分子较大并且表达量较高,目的蛋白质基本以包涵体的形式存在。包涵体中的蛋白质是无活性的蛋白质,为了获得有活性的蛋白质,就需要对包涵体进行变性及复性。尝试了一种新的凝胶色谱柱复性方法,并通过柱复性方法与常规的稀释复性方法进行了比较,发现柱复性方法明显优于稀释复性方法,具有成本低,效率高,并对目的蛋白质(DscuPA\|32K)进行了初步纯化等优点,尤其对酶这一类容易失活降解的蛋白质进行复性时,很值得进行推广应用。     

RGD-葡激酶的凝胶过滤层析法复性及其纯化

构建的溶栓和抗栓双重功能的RGD-葡激酶突变体(RGD-Sak)在大肠杆菌中高表达,目的蛋白质以包涵体形式存在。为获得有活性的蛋白质,需要对包涵体进行变复性。利用凝胶层析方法对包涵体中RGD-Sak进行复性,并与稀释复性法进行比较,发现凝胶柱复性方法具有操作周期短、简便、成本低而高效等优点。复性后蛋白质用Q-Sepharose FF离子交换进一步纯化,纯度达95%,酪蛋白凝胶板活性测定表明两种复性法得到的蛋白质比活性相当。圆二色谱测定显示两种复性法得到的蛋白质的二级结构成份和谱形一致,说明在两种复性过程中完成了RGD-Sak分子的正确折叠。     

蛇毒蛋白原核表达包涵体复性研究进展

外源基因在大肠杆菌中表达后常形成不溶性的无活性包涵体。包涵体的形成已经成为研究和应用活性蛋白质生产的主要障碍。然而,在合适的条件下,包涵体经过溶解、纯化、复性过程后可在体外重新折叠成有活性的蛋白质。迄今,已对蝰科、眼镜蛇科11种毒蛇的18个基因(包括金属蛋白酶、PLA₂、β-银环蛇毒素、心脏素素、丝氨酸蛋白酶、神经生长因子、C-型凝集素等)成功进行了原核表达,采用稀释复性、透析复性和层析复性三种方法成功进行了包涵体复性。着重就蛇毒蛋白原核表达后包涵体复性所用的方法予以综述。     

重组羧肽酶原B的复性方法研究

构建的羧肽酶原B表达质粒在大肠杆菌中获得高表达。但目的蛋白是以包涵体的形式存在。为了获得活性羧肽酶B,必须对其包涵体进行变复性。首先利用稀释复性确定了羧肽酶原B复性的最佳缓冲液;在凝胶过滤复性中,研究了柱长和洗脱流速对羧肽酶原B复性效率的影响;另外对比了稀释复性、透析复性、凝胶层析复性和Ni2 亲合层析法等四种方法对羧肽酶原B的复性效果。结果发现,这4种方法的复性效果有以下顺序:凝胶过滤复性>稀释复性>Ni2 亲合层析>透析复性。     

抗SARS 人源单链抗体H12的表达及复性

从SARS免疫抗体库获得的一株抗SARS-CoV人源单链抗体H12,亟待鉴定.为了快速制备大量具有生物活性的单链抗体H12,构建了pET28a-H12原核高表达载体,表达量占菌体总蛋白质30%以上.采用稀释复性和分子筛柱复性两种方法对包涵体蛋白进行复性与纯化,结果显示两种方法都能使得单链抗体复性.与稀释复性法相比,柱复性效果更好,其抗原结合活性是稀释复性法的1.51倍.柱复性后的单链抗体亲和力测定的解离常数Kd为73.5nmol/mL.为进一步研究单链抗体H12的功能奠定了基础.     

抗SARS 人源单链抗体H12的表达及复性

从SARS免疫抗体库获得的一株抗SARS-CoV人源单链抗体H12,亟待鉴定。为了快速制备大量具有生物活性的单链抗体H12,构建了pET28a-H12原核高表达载体,表达量占菌体总蛋白质30%以上。采用稀释复性和分子筛柱复性两种方法对包涵体蛋白进行复性与纯化,结果显示两种方法都能使得单链抗体复性。与稀释复性法相比,柱复性效果更好,其抗原结合活性是稀释复性法的1.51倍。柱复性后的单链抗体亲和力测定的解离常数K_d为73.5nmol/mL。为进一步研究单链抗体H12的功能奠定了基础。     

重组羧肽酶原B的复性方法研究*

构建的羧肽酶原B表达质粒在大肠杆菌中获得高表达。但目的蛋白是以包涵体的形式存在。为了获得活性羧肽酶B,必须对其包涵体进行变复性。首先利用稀释复性确定了羧肽酶原B复性的最佳缓冲液;在凝胶过滤复性中,研究了柱长和洗脱流速对羧肽酶原B复性效率的影响;另外对比了稀释复性、透析复性、凝胶层析复性和Ni²⁺亲合层析法等四种方法对羧肽酶原B的复性效果。结果发现,这4种方法的复性效果有以下顺序:凝胶过滤复性>稀释复性>Ni²⁺亲合层析>透析复性。     

一种从大肠杆菌包涵体中分离纯化GST-TRAF6融合蛋白的方法

利用8 mol/L尿素溶液对表达在大肠杆菌包涵体中的GST-TRAF6融合蛋白进行变性,通过逐级稀释复性的方法对尿素溶解后的GST-TRAF6融合蛋白进行复性,将复性后的GST-TRAF6融合蛋白进一步利用谷胱甘肽琼脂糖树脂亲和层析的方法进行分离纯化,将分离纯化后的蛋白通过Western blot方法进行验证,最后利用体外泛素化反应检测经包涵体变性、复性和纯化后的GST-TRAF6融合蛋白的生物学活性。经过包涵体变性、梯度稀释复性和谷胱甘肽琼脂糖树脂亲和层析3个步骤后纯化得到纯度达90%以上、浓度为396 ng/μL的蛋白质溶液。利用GST蛋白作为对照,经Western blot验证表明,纯化得到的蛋白确为GSTTRAF6融合蛋白。进一步利用体外泛素化反应分析其泛素连接酶活性发现,17 ng/μL浓度的GST-TRAF6融合蛋白能够以泛素分子作为底物在5 min内快速催化自由泛素链的生成。结果表明,表达在大肠杆菌包涵体中的GST-TRAF6融合蛋白经尿素变性溶解后能够成功复性并分离纯化,在溶解性改变的同时恢复了其泛素连接酶活性。为从大肠杆菌包涵体中大规模分离纯化蛋白质提供了一种新的复性方法。     

蛋白质的排阻色谱复性的新进展

外源蛋白在大肠杆菌中高效表达时 ,常常形成不溶的、无活性的包涵体 ,包涵体蛋白的复性是重组蛋白生产过程中的一个技术难题。排阻色谱 (sizeexclusionchromatography ,SEC)用于蛋白复性是一种较新的、适用于任何一种蛋白的方法 ,与常用的稀释复性法相比 ,它能在高的起始蛋白浓度下对蛋白进行复性 ,活性回收率较高 ,同时又能使目标蛋白得到一定程度的纯化。对使用SEC复性的进展进行了评述 ,其内容包括SEC复性的原理及其复性过程中的影响因素 ,并对其未来发展进行了展望。     

抑菌蛋白Reg3A的表达纯化与功能

利用原核表达系统表达人源抑菌蛋白Reg3A,经包涵体的复性和纯化获得有体外抑菌功能的活性抑菌蛋白,并对其体外抑菌功能进行初步研究。构建Reg3A原核表达载体PET-32a-Reg3A转化补充稀缺tRNA基因的表达菌株大肠杆菌BL21-Codonplus,阳性重组子采用诱导培养基诱导5h后,采用超声破碎的方法提取包涵体蛋白,经包涵体蛋白的纯化和透析复性后通过Ni-NTA亲和层析交换柱,获得纯度达95%的蛋白质。Western blot鉴定显示在15 kD处有特异性条带。使用纯化后的蛋白进一步进行抑菌圈实验和抑菌活性实验,对获得蛋白的体外抑菌活性进行评估,从而为进一步进行Reg3A蛋白功能的评估及应用奠定基础。     

重组抗血红素ScFv包涵体蛋白的复性及纯化研究

抗血红素多二硫键ScFv在大肠杆菌中绝大多数表达产物为包涵体,为了获得可溶性的具有生物活性的ScFv,摸索了不同的复性条件,包括透析法、稀释和层析相结合的方法。研究发现,先对溶解的变性ScFv溶液稀释,进行初步的蛋白质复性,再利用Sephadex G-25凝胶层析进一步复性、降低变性剂浓度和纯化,至少可以得到95％纯度,产率为150mg／L的目标蛋白,通过一次凝胶过滤层析,达到了去除变性剂、复性及纯化ScFv蛋白三种目的,为多二硫键ScFv在大肠杆菌中的表达和纯化提供了一种经济可行的方法。     

白细胞介素—2—绿脓杆菌外毒素融合蛋白的分高纯化及其复性研究

表达的白细胞介素－２－绿脓杆菌外毒素（ＩＬ－２－ＰＥ）融合蛋白以包含体形式存在于宿主菌中,为分离纯化表达产物提供了方便,但因需进行复性,也增加了后处理的难度．我们采用４ｍｏｌ／Ｌ尿素、０．５％ＴｒｉｔｏｎＸ－１００的１×ＰＢＳ洗涤包含体两遍,再经ＳｅｐｈａｃｒｙｌＳ－３００分子筛及ＤＥＡＥ－ＳｅｐｈａｒｏｓｅＦＦ阴离子交换柱层析后,获得的融合蛋白纯度可达９０％～９５％。此外,我们从ＧＳＳＧ浓度、Ｌ－精氨酸浓度、复性蛋白质的起始浓度、复性液的ｐＨ值、复性温度及复性时间等参数入手,系统地研究了融合蛋白的复性条件,探索到了ＩＬ－２－ＭＥ４０和ＩＬ－２－ＰＥ６６４Ｇｌｕ融合蛋白复性的最适条件。     

大肠杆菌表达的重组人PAI－1的纯化

纯化了工程细菌表达的可溶态和包含体形式的ｒｈＰＡＩ－１,纯度均达９８％,其ｒｈＰＡＩ－１蛋白质得率分别为１５％和１９％,比活性分别为３３５００ＩＵ／ｍｇ和２７７０００ＩＵ／ｍｇ。Ｎ端氨基酸序列分析显示,ｒｈＰＡＩ－１Ｎ端１５个氨基酸与天然ＰＡＩ－１完全一致;包含体复性研究表明,包含体的复性与复性蛋白的浓度及复性液中助溶剂的浓度密切相关。纯化的ｒｈＰＡＩ－１为分析ＰＡＩ－１结构与功能及探讨其临床应用提供了材料。     

Enhanced protein renaturation by temperature-responsive polymers

The application of temperature-sensitive polymer (PNIPAAm) for the renaturation of beta-lactamase from inclusion bodies was investigated. It was observed that PNIPAAm was more effective than PEG in enhancing protein renaturation. At a concentration of 0.1%, PNIPAAm improved the yield of beta-lactamase activity by 41% from 46. 5 to 65.4 IU/mL, compared to 26% with PEG from 46.5 to 58.7 IU/mL. Kinetic study indicated that PNIPAAm did not significantly affect the initial rate of protein renaturation but did increase final activity yield. In the presence of PEG and PNIPAAm, the activity yields increased with temperature, indicating that hydrophobic interactions between denatured protein and polymer molecules contributed to the enhanced protein renaturation with polymers. The sequential addition approach, aiming at enhancing protein renaturation by reducing local protein concentration during renaturation, was also shown effective in enhancing protein renaturation, especially in the presence of polymers. With the sequential addition approach, the activity yield was increased by 60. 5% from 46.5 to 74.6 IU/mL with PNIPAAm. Similar behavior was also observed with PEG. PNIPAAm exhibited similar behavior as PEG on the renaturation of beta-lactamase in terms of temperature effect and concentration effect, indicating that the mechanism for enhanced protein renaturation for the two polymers might be similar. PNIPAAm exhibits a lower critical solution temperature (LCST) of 32 degrees C and can be effectively separated from aqueous solution and recycled. A protein renaturation process employing PNIPAAm, which offers the advantages of enhanced renaturation efficiency, minimum loss of protein aggregates, and ease of polymers recycling, was proposed.     

A simplified bioprocess for human alpha-fetoprotein production from inclusion bodies

A simple and effective Escherichia coli (E. coli) bioprocess is demonstrated for the preparation of recombinant human alpha-fetoprotein (rhAFP), a pharmaceutically promising protein that has important immunomodulatory functions. The new rhAFP process employs only unit operations that are easy to scale and validate, and reduces the complexity embedded in existing inclusion body processing methods. A key requirement in the establishment of this process was the attainment of high purity rhAFP prior to protein refolding because (i) rhAFP binds easily to hydrophobic contaminants once refolded, and (ii) rhAFP aggregates during renaturation, in a contaminant- dependent way. In this work, direct protein extraction from cell suspension was coupled with a DNA precipitation-centrifugation step prior to purification using two simple chromatographic steps. Refolding was conducted using a single-step, redox-optimized dilution refolding protocol, with refolding success determined by reversed phase HPLC analysis, ELISA, and circular dichroism spectroscopy. Quantitation of DNA and protein contaminant loads after each unit operation showed that contaminant levels were reduced to levels comparable to traditional flowsheets. Protein microchemical modification due to carbamylation in this urea-based process was identified and minimized, yielding a final refolded and purified product that was significantly purified from carbamylated variants. Importantly, this work conclusively demonstrates, for the first time, that a chemical extraction process can substitute the more complex traditional inclusion body processing flowsheet, without compromising product purity and yield. This highly intensified and simplified process is expected to be of general utility for the preparation of other therapeutic candidates expressed as inclusion bodies.     

Oxidative renaturation of lysozyme at high concentrations

Newly synthesized cloned gene proteins expressed in bacteria frequently accumulate in insoluble aggregates or inclusion bodies. Active protein can be recovered by solubilization of inclusion bodies followed by renaturation of the solubilized (unfolded) protein. The recovery of active protein is highly dependent on the renaturation conditions chosen. The renaturation process is generally conducted at low protein concentrations (0.01-0.2 mg/mL) to avoid aggregation. We have investigated the potential of successfully refolding reduced and denatured hen egg white lysozyme at high concentrations (1 and 5 mg/mL). By varying the composition of the renaturation media, optimum conditions which kinetically favor proper folding over inactivation were found. Solubilizing agents such as guanidinium chloride (GdmCl) and folding aids such as L-arginine present in low concentrations during refolding effectively enhanced renaturation yields by suppressing aggregation resulting in reactivation yields as high as 95%. Quantitatively the kinetic competition between lysozyme folding and aggregation can be described using first-order kinetics for the renaturation reaction and third-order kinetics for the overall aggregation pathway. The rate constants for both reactions have been found to be strongly dependent on denaturant and thiol concentration. This strategy supercedes the necessity to reactivate proteins at low concentrations using large renaturation volumes. The marked increase in volumetric productivity makes this a viable option for recovering biologically active protein efficiently and in high yield in vitro from proteins produced as inclusion bodies within microbial cells. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 221-230, 1997.     

rPA(K)的原核表达及其产物的初步纯化

rPA(K)是经过缺失/定点突变技术所获得的t-PA突变体。本实验以IPTG诱导,实现了rPA(K)在原核系统中的表达。实验证明目的产物的表达形式为包涵体,且当以IPTG诱导3h时,表达量最高,为41%。此后对该表达产物进行了初步纯化,即通过对不同超声破碎次数,包涵体洗涤液(脲,Triton X-100,乙醇)的不同浓度对纯化的影响因素进行了摸索。结果表明,超声2次,2M脲,0.5%Triton X-100,20%乙醇对目的蛋白纯化的效果最好,从而为进一步的纯化和复性奠定基础。     

精氨酸、精氨酸盐酸、半胱氨酸、胱氨酸对重组人tPA蛋白复性的影响

以重组人tPA蛋白为材料研究了精氨酸、精氨酸盐酸盐、半胱氨酸、胱氨酸对蛋白质复性效果的影响,重组tPA蛋白包涵体经尿素变性溶解后,在精氨酸、精氨酸盐酸盐、半胱氨酸、胱氨酸存在的条件下进行复性,结果表明,碱性的精氨酸在质量分数0.2%时可减少蛋白质凝聚,显著提高复性效果,tPA复性后的活性可提高50%以上,半胱氨酸单独使用具有类似β-巯基乙醇的作用,精氨酸盐酸盐和胱氨酸单独使用对复性无影响,而半胱氨酸和胱氨酸联合使用,有类似氧化-还原系统作用。可提高活性20%。     

包涵体蛋白体外复性的研究进展

外源基因在大肠杆菌中高水平表达时 ,通常会形成无活性的蛋白聚集体即包涵体。包涵体富含表达的重组蛋白 ,经分离、变性溶解后须再经过一个合适的复性过程实现变性蛋白的重折叠 ,才能够得到生物活性蛋白。近年来 ,发展了许多特异的策略和方法来从包涵体中复性重组蛋白。最近的进展包括固定化复性以及用一些低分子量的添加剂等来减少复性过程中蛋白质的聚集 ,提高活性蛋白的产率。