IMPACT-TWIN蛋白纯化系统的机制及其应用

IMPACT-TWIN系统是一种新型的蛋白融合表达及纯化系统,已被应用到蛋白质工程的众多领域。此系统中目的蛋白与蛋白自剪接元件intein及几丁质结合蛋白域CBD构成融合蛋白,利用几丁质亲和层析柱,通过诱导内含肽的肽键裂解活性,使目的蛋白释放出来,而内含肽与几丁质结合蛋白仍结合在几丁质介质上,实现了单柱分离纯化蛋白。本文主要阐述了IMPACT-TWIN蛋白表达纯化系统的机制、特点,以及其在蛋白表达纯化方面应用的最新进展。     

重组血管活性肠肽的制备及鉴定

为利用基因工程技术获得重组血管活性肠肽(vasoactive intestinal peptide,VIP),根据大肠杆菌的密码偏好性,设计并人工合成编码28个氨基酸的VIP基因。克隆到表达载体PTWIN,构建重组质粒PTWIN-VIP,转化宿主菌E. coli Strain ER2566,构建表达工程菌。实现由重组VIP,内含肽与纤维素结合域（cellulose binding domain, CBD）组成的融合蛋白表达。融合蛋白经几丁质亲和层析纯化,通过改变温度和缓冲液PH值切割融合蛋白,获得目的多肽。所得的多肽经质谱测定分子量结果与理论值相符。生物活性分析表明,重组VIP能显著降低急性炎症小鼠血清中抵抗素的水平,发挥抗炎作用。重组VIP的制备及其抗炎活性的鉴定为其深入开发奠定了基础。     

重组Maxadilan的制备与鉴定

为利用基因工程技术获得重组Maxadilan(RMMAX), 根据Maxadilan的氨基酸序列, 设计并人工合成了在原核表达的基因。克隆到表达载体pKYB, 重组质粒pKYB-MAX转化表达宿主菌Escherichia coli strain ER2566, 构建表达工程菌。用诱导剂IPTG诱导由目的多肽、内含肽和几丁质结合域(Chitin binding domain, CBD)组成的“三元”融合蛋白表达; 用几丁质珠亲和层析纯化了裂解液中的融合蛋白, 用b-巯基乙醇切割融合蛋白, 获得目的蛋白。所得的多肽经激光飞行质谱测定分子量结果与理论值相符, 生物活性分析表明, 重组Maxadilan有显著的提升血糖的作用。     

胸腺肽α1-Spl DnaX内含肽融合蛋白的切割动力学研究

目的:研究胸腺肽α1(Tα1)与Spl DnaX内含肽融合蛋白AS的体外切割动力学。方法:构建Tα1和SplDnaX内含肽的融合表达载体pET-AS,转化大肠杆菌BL21(DE3),经乳糖诱导获得可溶性表达的融合蛋白AS,用镍亲和层析纯化该蛋白;综合评价温度、β-巯基乙醇(β-ME)浓度和诱导切割时间对Spl DnaX内含肽介导融合蛋白AS自切割释放Tα1的影响。结果:在大肠杆菌中诱导表达了融合蛋白AS,经镍柱纯化获得该蛋白;随着温度升高和β-ME浓度增加,诱导切割时间延长,Spl DnaX内含肽介导的切割率逐渐增大;最终采用300 mmol/Lβ-ME切割24 h,融合蛋白的硫解切割率大于90%。结论:通过对Spl DnaX内含肽的诱导切割条件进行摸索,确定了最适宜的切割条件,为利用该方法制备Tα1和其他小分子多肽提供了技术基础。     

蛋白内含子介导纯化的表达载体的构建及应用

将抗膀胱癌单链抗体(PG)融合在蛋白内含子(intein)的C末端,利用intein的N末端具有的chitin binding domain(CBD)对几丁质柱的吸附特性及intein的自切割活性对PG进行一次性纯化。同时,引入大肠杆菌分子伴侣肽基脯氨酰顺反异构酶(FkpA)与目的蛋白进行共表达及融合表达,以使目的蛋白以可溶形式存在。结果显示,PG融合蛋白对几丁质柱的吸附效率很高,intein的自切割释放PG的效率也较高,但PG仅出现在SDS洗脱液中。FM与PG共表达能显著地提高目的蛋白的可溶性。Intein介导的纯化系统前景远大。     

新型断裂内含肽介导的可控性C端断裂

内含肽介导的蛋白质断裂被广泛地应用于蛋白质纯化、连接和环化. 但目前的方法都是用传统的连续的内含肽来介导蛋白质断裂反应,因而往往存在自发性断裂、产率低等问题. 本实验选择3个S1型新型断裂内含肽Ter ThyX、Ssp GryB和Rma DnaB来实现蛋白质断裂反应的可控性. 在可控性C端断裂反应中,S1型断裂内含肽的C端片段（IC ）与硫氧还蛋白（T）融合作为前体蛋白,加入化学合成的Ssp DnaB S1型断裂内含肽 的N端小肽与二硫苏糖醇（DTT）共同诱导C端断裂反应.结果表明,该小肽可以诱导这 3个不同的S1型断裂内含肽的前体蛋白发生C端断裂反应. 该方法为利用内含肽C端断 裂介导的蛋白质纯化提供了更多的选择,并为内含肽的结构与功能的关系研究提供-有用的线索.     

双Intein介导3片段vWF的反式剪接

von Willebrand因子(vWF)基因突变导致血管性血友病(VWD),由于其基因过大在基因治疗研究中难以为多数病毒载体携带.利用双内含肽(intein)的蛋白质反式剪接功能研究断裂成3段的vWF基因分别表达后在蛋白水平的连接,旨在为vWF基因的3载体联合转移应用于VWD基因治疗研究提供依据.将vWF cDNA于满足剪接所需的保守性氨基酸Cys1099、Ser2004的密码子前断裂为3段(N、M和C),分别与splitSspDnaE intein的N端(En)、C端(Ec)和splitSspDnaB intein的N端(Bn)、C端(Bc)编码序列融合,构建到原核表达载体pET-28a(+)中的His-Tag的下游,得到3种表达载体pET-NEn、pET-EcMBn和pET-BcC.分别转化感受态大肠杆菌BL21(DE3)细胞,经IPTG诱导表达后,以SDS-PAGE分析融合蛋白的表达,并进一步用His-Tag的特异性抗体进行分析;亲和层析纯化分别表达的带His-Tag标签的3段蛋白,复性后体外混合进行剪接实验以观察3片段vWF的连接.结果显示,3段预期大小的融合intein的vWF蛋白均有表达,用His-Tag抗体进行的Western印迹得到进一步证实;3段纯化的蛋白混合后可见明显的剪接条带形成,与vWF的预期分子量大小一致,表明双intein通过蛋白质反式剪接可有效连接3个片段的vWF,为进一步应用蛋白质剪接技术的3重载体真核细胞转vWF基因奠定了基础.     

DnaB Split Intein高表达载体及其介导的环肽库构建

以pET28a为起始质粒,构建高表达DnaB split intein的重组质粒.将质粒pVmut上的编码IntC-dnaB-N-IntN片段克隆至pET28a,得到表达载体pEV,在T7启动子的作用下可使融合DnaB split intein大量表达;并在split intein介导下发生催化DnaB-N的剪接反应,生成环化的DnaB-N蛋白.将合成的包含随机编码5肽的大小为115 bp的片段插入质粒pEV DnaB-N位置,转化大肠杆菌后得到一个编码含有6肽(含5个随机氨基酸和1个Cys)的包含约103个克隆的表达载体pEV-IS库.随机挑取20个克隆,测序证明均按正确阅读框插入了不同的小肽序列;挑取其中9个克隆进行表达.结果表明可产生大量的融合蛋白,90%的融合蛋白在16℃表达20 h后发生体内剪接.将在30℃表达3 h的融合蛋白用His柱进行纯化,通过MALDI-TOF质谱检测到了目的环肽分子量.     

新型抗2-型糖尿病基因重组RMBAY的克隆、表达及生产环节优化

利用基因重组方法构建RMBAY的原核表达载体pKY-BAY,并研究其生产的优化条件。选用大肠杆菌偏爱密码子,用PCR方法合成全长RMBAY多肽基因,并定向插入到高效表达载体pKYB-mcs中,用大肠杆菌ER2566进行表达,融合蛋白经Chitin-Beads柱纯化后,结合在柱上的融合蛋白用β-巯基乙醇诱导蛋白内含肽的N端自动切割,释放目的肽,目的肽由质谱鉴定。 实验结果表明：利用载体pKY-B在大肠杆菌ER2566中,RMBAY能够实现高效表达;在优化的生产条件下,RMBAY的产量可达到6.7mg/L发酵产物,纯度大于98%,质谱鉴定RMBAY的分子量为3.887kDa. 与理论值相符合。     

内毒素结合肽的原核表达、纯化及生物学活性鉴定

重组人内毒素结合肽 (endotoxinbindingpeptide ,EBP)融合蛋白在大肠杆菌中表达 ,分离和纯化后对其进行生物学活性观察 .将构建好的PinpointⅩa3 EBP生物素融合表达载体转化大肠杆菌DH5α ,IPTG诱导表达菌株 ,亲和层析法纯化表达产物 ,因子Ⅹa(factorⅩa)切割分离内毒素结合肽 ,采用凝胶过滤和反相液相高效色谱法两步纯化 ,从相对分子质量、N端 1 0个氨基酸的序列分析等方面进行鉴定 ;利用人单核细胞U937对重组内毒素结合肽进行了生物学活性的检测 .结果发现 ,内毒素结合肽以包涵体形式存在 ,因子Ⅹa酶切融合蛋白后得到 3 5kD的内毒素结合肽 ,纯化后内毒素结合肽纯度达 99%以上 ,N端 1 0个氨基酸的分析结果与预期相符 ;初步证实内毒素结合肽具有较好的LPS结合活性 ,能够抑制LPS的作用 .经原核表达及纯化复性 ,获得了具有较好生物学活性的内毒素结合肽 ,为进一步研究其功能奠定了良好的基础     

Construction of a mini-intein fusion system to allow both direct monitoring of soluble protein expression and rapid purification of target proteins

Affinity purification of recombinant proteins has been facilitated by fusion to a modified protein splicing element (intein). The fusion protein expression can be further improved by fusion to a mini-intein, i.e. an intein that lacks an endonuclease domain. We synthesized three mini-inteins using overlapping oligonucleotides to incorporate Escherichia coli optimized codons and allow convenient insertion of an affinity tag between the intein (predicted) N- and C-terminal fragments. After examining the splicing and cleavage activities of the synthesized mini-inteins, we chose the mini-intein most efficient in thiol-induced N-terminal cleavage for constructing a novel intein fusion system. In this system, green fluorescent protein (GFP) was fused to the C-terminus of the affinity-tagged mini-intein whose N-terminus was fused to a target protein. The design of the system allowed easy monitoring of soluble fusion protein expression by following GFP fluorescence, and rapid purification of the target protein through the intein-mediated cleavage reaction. A total of 17 target proteins were tested in this intein-GFP fusion system. Our data demonstrated that the fluorescence of the induced cells could be used to measure soluble expression of the intein fusion proteins and efficient intein cleavage activity. The final yield of the target proteins exhibited a linear relationship with whole cell fluorescence. The intein-GFP system may provide a simple route for monitoring real time soluble protein expression, predicting final product yields, and screening the expression of a large number of recombinant proteins for rapid purification in high throughput applications.     

Expression of SMAP-29 cathelicidin-like peptide in bacterial cells by intein-mediated system

In this work, the intein fusion approach was used for expression and purification of cathelicidin-like peptide SMAP-29 from Escherichia coli cultures. To overcome the high toxicity of the antimicrobial peptide against host cells, both C- and N-terminal fusions with Sce VMA intein were evaluated. The fusion of SMAP-29 with the N-terminus of intein had a dramatic lethal effect. In contrast, chimeric constructs harboring SMAP-29 linked to the C-terminus of intein displayed no significant inhibition of bacterial growth. Expression of intein-SMAP fusion protein was then induced in ER2566 E. coli strain by IPTG addition and different experimental conditions were tested in order to optimize the recovery of the soluble protein complex. Peptide purification was carried out by affinity chromatography: the chitin binding domain linked to intein was used to immobilize the chimeric protein on a chitin column and intein-mediated splicing of target peptide was obtained by thiol addition. Microbroth dilution assay showed that recombinant SMAP-29 displayed a high, dose-dependent bactericidal activity. These data demonstrate that the fusion of SMAP-29 with C-intein was able to inactivate the antimicrobial properties of the cathelicidin peptide allowing the expression of fusion protein in the host cell. The intein-mediated purification supplied an effective way to recover the fusion partner in its proper biologically active form.     

蛋白质剪切及其应用

蛋白质剪切是一种翻译后修饰事件 ,它将插入前体蛋白的中间的蛋白质肽段 (Intein ,internalproteinfrag ment)剪切出来 ,并用正常肽键将两侧蛋白质多肽链 (Extein ,flankingproteinfragments)连接起来。在此过程中不需要辅酶或辅助因子的作用 ,仅需四步分子内反应。Intein及其侧翼序列可以通过突变产生高度特异性的自我切割用于蛋白质纯化、蛋白质连接和蛋白质环化反应 ,在蛋白质工程方面有广泛的应用前景。     

Study of protein splicing and intein-mediated peptide bond cleavage under high-cell-density conditions

Protein splicing elements (inteins), capable of catalyzing controllable peptide bond cleavage reactions, have been used to separate recombinant proteins from affinity tags during affinity purification. Since the inteins eliminate the use of a protease in the recovery process, the intein-mediated purification system has the potential to significantly reduce recovery costs for the industrial production of recombinant proteins. Thus far, the intein system has only been examined and utilized for expression and purification of recombinant proteins at the laboratory scale for cells cultivated at low cell densities. In this study, protein splicing and in vitro cleavage of intein fusion proteins expressed in high-cell-density fed-batch fermentations of recombinant Escherichia coli were examined. Three model intein fusion constructs were used to examine the stability and splicing/cleavage activities of the fusion proteins produced under high-cell-density conditions. The data indicated that the intein fusion protein containing the wild-type intein catalyzed efficient in vivo protein splicing during high-cell-density cultivation. Also, the intein fusion proteins containing modified inteins catalyzed efficient thiol-induced in vitro cleavage reactions. The results of this study demonstrated the potential feasibility of using the intein-mediated protein purification system for industrial-scale production of recombinant proteins.     

Production of the catalytic core of human peptidylglycine α-hydroxylating monooxygenase (hPHMcc) in Escherichia coli

Most mammalian bioactive peptides possess a C-terminal amino acid amide moiety. The presence of the C-terminal amide is a significant impediment to the recombinant production of α-amidated peptides. α-Amidated peptides are produced in vivo by the enzymatic cleavage of a precursor with a C-terminal glycine residue. Peptidylglycine α-hydroxylating monooxygenase catalyzes the key step in the oxidation of the glycine-extended precursors to the α-amidated peptide. Herein, we detail the production of the catalytic core of human peptidylglycine α-hydroxylating monooxygenase (hPHMcc) in Escherichia coli possessing a N-terminal fusion to thioredoxin (Trx). Trx was fused to hPHMcc to enhance the yield of the resulting 52 kDa protein as a soluble and catalytically active enzyme. The Trx-hPHMcc-His(6) fusion was purified to homogeneity and exhibited steady-state kinetic parameters that were similar to purified rat PHMcc. The bacterial production of recombinant hPHMcc will foster efforts to generate α-amidated peptides by the co-expression of hPHMcc and the α-amidated peptide precursors in E. coli or the in vitro amidation of recombinantly expressed α-amidated peptide precursors.     

In vivo analysis of fibroin heavy chain signal peptide of silkworm Bombyx mori using recombinant baculovirus as vector

In order to investigate the functional signal peptide of silkworm fibroin heavy chain (FibH) and the effect of N- and C-terminal parts of FibH on the secretion of FibH in vivo, N- and C-terminal segments of fibh gene were fused with enhanced green fluorescent protein (EGFP) gene. The fused gene was then introduced into silkworm larvae and expressed in silk gland using recombinant AcMNPV (Autographa californica multiple nuclear polyhedrosis virus) as vector. The fluorescence of EGFP was observed with fluorescence microscope. FibH-EGFP fusion proteins extracted from silk gland were analyzed by Western blot. Results showed that the two alpha helices within N-terminal 163 amino acid residues and the C-terminal 61 amino acid residues were not necessary for cleavage of signal peptide and secretion of the fusion protein into silk gland. Then the C-terminal 61 amino acid residues were substituted with a His-tag in the fusion protein to facilitate the purification. N-terminal sequencing of the purified protein showed that the signal cleavage site is between position 21 and 22 amino acid residues.     

Intein-mediated rapid purification of recombinant human pituitary adenylate cyclase activating polypeptide

In order to obtain the recombinant human PACAP efficiently by intein-mediated single column purification, a gene encoding human PACAP was synthesized and cloned into Escherichia coli expression vector pKYB. The recombinant vector pKY-PAC was transferred into E. coli ER2566 cells and the target protein was over-expressed as     

Utilizing the C-terminal cleavage activity of a protein splicing element to purify recombinant proteins in a single chromatographic step.

A conventional affinity protein purification system often requires a separate protease to separate the target protein from the affinity tag. This paper describes a unique protein purification system in which the target protein is fused to the C-terminus of a modified protein splicing element (intein). A small affinity tag is inserted in a loop region of the endonuclease domain of the intein to allow affinity purification. Specific mutations at the C-terminal splice junction of the intein allow controllable C-terminal peptide bond cleavage. The cleavage is triggered by addition of thiols such as dithiothreitol or free cysteine, resulting in elution of the target protein while the affinity-tagged intein remains immobilized on the affinity column. This system eliminates the need for a separate protease and allows purification of a target protein without the N-terminal methionine. We have constructed general cloning vectors and demonstrated single-column purification of several proteins. In addition, we discuss several factors that may affect the C-terminal peptide bond cleavage activity.