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。     

重组蛋白ApSerpin-FA72的包涵体复性及活性研究

[目的]原核表达及制备重组光滑鳖甲丝氨酸蛋白酶抑制剂(Ap Serpin-FA72),探索包涵体最优复性条件与最适酶反应条件。[方法]采用超声破碎获得大量包涵体,通过包涵体的洗涤、包涵体的溶解方法对包涵体进行纯化,获得高纯度的包涵体进行复性液成分与复性方法的摸索。测定Trx A-Ap Serpin-FA72对胰蛋白酶的IC50、最适反应p H和最适反应温度。[结果]在32℃、180 r/min、0. 4 mmol/L IPTG浓度下以沉淀形式表达大量蛋白,通过包涵体复性在含有L-精氨酸复性液中获得有生物活性的Trx A-Ap Serpin-FA72,对胰蛋白酶的IC50为0. 48μmol/L,p H在7～9,温度在60℃时有较高的抑制活性。[结论]L-精氨酸是复性液中重要的组成部分,复性的重组蛋白Trx A-Ap SerpinFA72对胰蛋白酶有较强的抑制能力,是一种热稳定较好的弱碱性胰蛋白酶抑制剂。     

刺桐属胰蛋白酶抑制剂的结构与生物活性关系

刺桐胰蛋白酶抑制剂（ETI）属于丝氨酸蛋白酶抑制剂,它能和胰蛋白酶及瑞替普酶（r-PA）等精氨酸特征性的丝氨酸蛋白酶发生了可逆亲合作用,根据此特性可将ETI作为固定配基制备成亲合填料,用于大规模高效分离r-PA,满足临床对溶栓制剂r-PA的大量需求,本对刺桐属胰蛋白酶抑制剂的结构与抑制活性关系进行综述。     

HIV-1蛋白酶的表达、纯化及其抑制剂体外筛选方法的建立

从HIV-1IIIB病毒RNA经RT-PCR得到HIV-1蛋白酶编码序列,克隆到pet28a质粒中构建HIV-1蛋白酶表达载体。阳性克隆转染E.coliBL21DE3,经IPTG诱导,蛋白酶以包涵体的形式表达,表达量占菌体总蛋白量的40%。包涵体经TritonX-100洗涤后溶解于8M尿素,溶解后的蛋白溶液经sephacyls-200H.R分子筛柱纯化后纯度达到90%以上,收集蛋白酶峰稀释复性并通过超滤进行浓缩。经检测,纯化的蛋白酶具有较高的活性。用荧光标记的蛋白酶底物检测不同浓度indinavir对蛋白酶活性的影响,表明该方法可以用于蛋白酶抑制剂的筛选。     

HIV-1蛋白酶的表达、纯化及其抑制剂体外筛选方法的建立

从HIV-1 ⅢB病毒RNA经RT-PCR得到HIV-1蛋白酶编码序列,克隆到pet28a质粒中构建HIV-1蛋白酶表达载体.阳性克隆转染E.coli BL21 DE3,经IPTG诱导,蛋白酶以包涵体的形式表达,表达量占菌体总蛋白量的40%.包涵体经Triton X-100洗涤后溶解于8M尿素,溶解后的蛋白溶液经sephacyl s-200 H.R分子筛柱纯化后纯度达到90%以上,收集蛋白酶峰稀释复性并通过超滤进行浓缩.经检测,纯化的蛋白酶具有较高的活性.用荧光标记的蛋白酶底物检测不同浓度indinavir对蛋白酶活性的影响,表明该方法可以用于蛋白酶抑制剂的筛选.     

苜蓿夜蛾中肠丝氨酸蛋白酶cDNA的克隆、序列分析及原核表达

【目的】本研究旨在从苜蓿夜蛾Heliothis viriplaca中肠克隆出丝氨酸蛋白酶（serine protease, SP）基因的cDNA序列,测定原核表达后的蛋白经纯化及复性后的活性。【方法】运用RT-PCR和cDNA末端快速扩增方法（rapid amplification of cDNA ends, RACE）克隆苜蓿夜蛾幼虫中肠丝氨酸蛋白酶cDNA全序列,用大肠杆菌Escherichia coli表达系统进行表达。重组蛋白经纯化后,利用梯度透析法进行复性,以BApNA为底物,进行活性测定。【结果】克隆获得的苜蓿夜蛾中肠丝氨酸蛋白酶基因命名为HvSP（GenBank登录号：JX866720）,该基因全长880 bp,开放阅读框长762 bp,编码254个氨基酸,推测分子量和pI值分别为26.9 kDa和9.49。由HvSP推导的氨基酸与鳞翅目昆虫SP氨基酸序列的一致性在52%~95%之间,其中与棉铃虫Helicoverpa armigera SP（GenBank登录号：CAA72962）的氨基酸序列一致性最高,达95%。成功构建重组载体pET21b-HvSP进行原核表达,Western-blot鉴定确定为目的蛋白。蛋白可溶性分析发现重组蛋白为包涵体。在Glycine-NaOH缓冲液中,当pH为10.0时,复性的重组蛋白活性达到最高,为35.74 U/mL。【结论】本研究在苜蓿夜蛾体内获得了一个新的丝氨酸蛋白酶基因,且原核表达后的重组蛋白经过变性、纯化及复性后具有活性。该结果为进一步研究丝氨酸蛋白酶在鳞翅目昆虫体内的生理功能奠定了基础。     

蛇毒丝氨酸蛋白酶

蛇毒是含有许多种生物活性蛋白质和多肽的复杂混合物 ,在蛇毒中蛋白酶占据着独特的位置 ,特别是蝰亚科和蝮亚科。目前可将蛇毒中蛋白水解酶主要分成两大类 ,其中一类是可被ＰＭＳＦ或ＤＦＰ抑制其活性的丝氨酸蛋白酶类。它们的蛋白质序列与胰蛋白酶、激肽释放酶比较显示较大同源性 ,均具有一个共同活性中心和相同的酶催化机制。但由于活性中心外的序列差异导致底物专一性差异和生物活性差异。另一类是可被金属螯合剂ＥＤＴＡ抑制其活性的金属蛋白酶类。一般说来 ,参加它们催化作用活性中心的金属离子是锌 ,隶属于一个新的金属蛋白酶亚科 (ｍ…     

光滑鳖甲丝氨酸蛋白酶抑制剂基因ApSerpin-FA72的克隆、表达及功能验证

【目的】本研究旨在对光滑鳖甲Anatolica polita borealis丝氨酸蛋白酶抑制剂基因进行克隆及表达分析,以验证光滑鳖甲丝氨酸蛋白酶抑制剂的功能。【方法】利用PCR和cDNA末端快速扩增(rapid amplification of cDNA ends,RACE)技术克隆获得光滑鳖甲丝氨酸蛋白酶抑制剂基因。采用生物信息学方法对该基因及其编码蛋白的基本性质进行预测和分析,同时构建其编码产物的系统进化树;构建光滑鳖甲丝氨酸蛋白酶抑制剂蛋白重组表达载体,表达、纯化蛋白进行功能验证。【结果】获得光滑鳖甲丝氨酸蛋白酶抑制剂基因Ap Serpin-FA72(Gen Bank登录号:MF188125),其基因编码序列长为1 176 bp,编码由391个氨基酸残基组成的多肽,蛋白理论分子量为43.7 k D,理论等电点为5.14,包含一个由21个氨基酸组成的信号肽。As Serpin-FA72属亲水蛋白,分泌到胞外发挥作用,可能具有胁迫应答的功能,与赤拟谷盗Triboloum castaneum Serpin的同源性最高。纯化得到的融合蛋白Trx A-Ap Serpin-FA72大小约为63.7 k D。功能验证表明,重组蛋白Trx A-Ap SerpinFA72对胰蛋白酶及胰凝乳蛋白酶活性均有抑制作用。【结论】光滑鳖甲丝氨酸蛋白酶抑制剂基因的表达产物对胰蛋白酶及胰凝乳蛋白酶活性具有抑制作用,表明其可能对消化类丝氨酸蛋白酶活性起抑制作用,对其功能活性的验证有助于深入研究Ap Serpin-FA72与丝氨酸蛋白酶之间的关系。     

ATF-PAI2CD融合蛋白的生物学功能

为了解尿激酶型纤溶酶激活物 (urokinase typeplaminogenactivator,uPA)的氨基末端片段 (amino terminalfrag ment,ATF)和纤溶酶激活物抑制剂 2 (plasminogenactivatorinhibitortype 2 ,PAI 2 )突变体PAI 2CD融合蛋白在大肠杆菌的表达情况及进一步研究其生物学活性、将ATF PAI2CD融合基因与大肠杆菌表达载体pLY 4重组得到表达质粒pZWE ATF PAI2CD ,以其转化大肠杆菌JF112 5 ,经温度诱导 ,ATF PAI2CD获得较高水平表达 ,融合蛋白质以包涵体形式存在 ,占菌体总蛋白质的 15 %。包涵体经洗涤、8mol L尿素溶解、稀释复性及离子交换色谱一步分离 ,纯度达 90 % ,分子量与理论值相符。每升发酵液得重组融合蛋白质 5 0mg。经牛奶板法检测具有纤溶抑制活性 ,比活性达 12 0 0 0IU mg ;应用放射竞争法证实融合蛋白质能与肿瘤细胞表面的uPA受体特异性结合。双功能融合蛋白质的纤溶抑制活性与野生型PAI 2 (或PAI 2突变体 ,PAI 2CD)基本一致 ,与肿瘤细胞表面的uPA受体的结合能力同pro uPA。     

刺桐胰蛋白酶抑制剂亲和填料的制备及纯化瑞替普酶

刺桐属胰蛋白酶抑制剂(ETI)是一种丝氨酸蛋白酶抑制剂,能特异性的抑制胰蛋白酶、组织纤溶酶原激活剂(tPA)、瑞替普酶(rPA)等丝氨酸蛋白酶。实验利用ETI工程菌,经诱导表达、体外复性及纯化获得ETI蛋白,并将该蛋白键合到CNBr活化的琼脂糖凝胶,制备ETI亲和填料,纯化瑞替普酶 。     

High-level expression and purification of Escherichia coli oligopeptidase B

Oligopeptidase B (OpdB) of Escherichia coli, previously called protease II, has a trypsin-like specificity, cleaving peptides at lysine and arginine residues and belongs to the prolyl oligopeptidase family of new serine peptidases. In this study, we report the fusion expression of E. coli oligopeptidase B with an N-terminal histidine tag using pET28a as the expression vector. Although most of the recombinant OpdB was produced as inclusion bodies, the solubility of the recombinant protease increased significantly when the expression temperature shifted from 37 to 30 degrees C. Recombinant OpdB (approximately 10 mg) could be purified from the soluble fraction of the crude extract of 1L log-phase E. coli culture containing 1.5 g wet bacterial cells. The purified OpdB has a molecular weight of approximately 80 kDa and a specific activity of 4.8 x 10(4) U/mg. OpdB could also be purified from the inclusion bodies with a lower yield. The recombinant enzyme was very stable under 40 degrees C. By comparison of the substrate specificity of the purified OpdB with that of OpdA, another trypsin-like protease in E. coli, we found that Boc-Glu-Lys-Lys-MCA is a specific substrate for E. coli OpdB. We also found that compared to OpdA, OpdB is much more sensitive to GMCHA-OPh(t)Bu, a synthetic trypsin inhibitor that can retard the growth of E. coli.     

Structural basis of trypsin inhibition and entomotoxicity of cospin, serine protease inhibitor involved in defense of Coprinopsis cinerea fruiting bodies

Cospin (PIC1) from Coprinopsis cinerea is a serine protease inhibitor with biochemical properties similar to those of the previously characterized fungal serine protease inhibitors, cnispin from Clitocybe nebularis and LeSPI from Lentinus edodes, classified in the family I66 of the MEROPS protease inhibitor classification. In particular, it exhibits a highly specific inhibitory profile as a very strong inhibitor of trypsin with K(i) in the picomolar range. Determination of the crystal structure revealed that the protein has a β-trefoil fold. Site-directed mutagenesis and mass spectrometry results have confirmed Arg-27 as the reactive binding site for trypsin inhibition. The loop containing Arg-27 is positioned between the β2 and β3 strands, distinguishing cospin from other β-trefoil-fold serine protease inhibitors in which β4-β5 or β5-β6 loops are involved in protease inhibition. Biotoxicity assays of cospin on various model organisms revealed a strong and specific entomotoxic activity against Drosophila melanogaster. The inhibitory inactive R27N mutant was not entomotoxic, associating toxicity with inhibitory activity. Along with the abundance of cospin in fruiting bodies of C. cinerea and the lack of trypsin-like proteases in the C. cinerea genome, these results suggest that cospin and its homologs are effectors of a fungal defense mechanism against fungivorous insects that function by specific inhibition of serine proteases in the insect gut.     

In situ proteolytic digestion of inclusion body polypeptides occurs as a cascade process

Misfolded proteins undergo a preferent degradation ruled by the housekeeping bacterial proteolytic system, but upon precipitation as inclusion bodies their stability dramatically increases. The susceptibility of aggregated polypeptides to proteolytic attack remains essentially unexplored in bacteria and also in eukaryotic cells. We have studied here the in vitro proteolysis of beta-galactosidase fusion proteins by trypsin treatment of purified inclusion bodies. A cascade digestion process similar to that occurring in vivo has been observed in the insoluble fraction of the digestion reaction. This suggests that major protease target sites are not either lost or newly generated by protein precipitation and that the digestion occurs in situ probably on solvent-exposed surfaces of inclusion bodies. In addition, the sequence of the proteolytic attack is influenced by protein determinants other than amino acid sequence, the early digestion steps having a dramatic influence on the further cleavage susceptibility of the intermediate degradation fragments. These observations indicate unexpected conformational changes of inclusion body proteins during their site-limited digestion, that could promote protein release from aggregates, thus partially accounting for the plasticity of in vivo protein precipitation and solubilization in bacteria.     

Refolding and structural characteristic of TRAIL/Apo2L inclusion bodies from different specific growth rates of recombinant Escherichia coli

TNF-related apoptosis-inducing ligand (TRAIL/Apo2L) was produced mainly as inclusion bodies (IBs) by recombinant Escherichia coli with a temperature-inducible expression system. The yield of TRAIL type 2 IBs at higher preinduction specific growth rate (mu = 0.15 h-1) was higher than that of TRAIL type 1 IBs at lower preinduction specific growth rate (mu = 0.05 h-1). With the same optimized refolding protocols, two types of IBs exhibited different refolding features. Refolded type 1 IBs had higher recovery of more than 80% compared with type 2 IBs (57-63%). By the measurements of fluorescence and CD spectroscopy, type 1 TRAIL IBs dissolved by urea appeared to be a closer secondary structure to the native TRAIL than type 2. Furthermore, with trypsin treatment, the striking decrease in stability of type 1 IBs against protease digestion cannot be attributed to their small size particles observed by scanning electron microscope and probably depend on different protein structure properties between the two IBs. Different properties of inclusion bodies were mainly influenced by different physiological states of the cells just prior to the induction.     

Three-dimensional structure of protein C inhibitor predicted from structure of alpha 1-antitrypsin with computer graphics

The three-dimensional structure of a proteolytically modified protein C inhibitor, a member of the serine protease inhibitor superfamily, was constructed with computer graphics based on its amino acid sequence homology with that of the modified alpha 1-antitrypsin whose structure had been elucidated by X-ray crystallography. The intact form of protein C inhibitor was predicted with an alpha-carbon model based on its hydrophilicity and hydrogen bond pattern. Furthermore, a model of its interaction with activated protein C was constructed based on the structure of the complex between trypsin and its inhibitor, which had been determined by X-ray crystallography.     

Expression of a kallikrein-like protease from the snake venom: engineering of autocatalytic site in the fusion protein to facilitate protein refolding

In order to circumvent the difficulty encountered in the expression and purification of the recombinant products in E. coli system, we have developed a novel and facile method of removing the polyhistidine tag from target proteins after heterologous gene expression. The expression of a serine protease (Tm-5) from Taiwan habu (Trimeresurus mucrosquamatus) is taken as an exemplar to illustrate the basic rationales and protocols involved. In place of an enterokinase recognition site, a polyhistidine tag linked to an autocatalyzed site based on cleavage specificity of the serine protease flanking on the 5'-end of Tm-5 clone sequence was engineered before protein expression in E. coli system. Renaturation of the fusion protein after expression revealed that the recombinant protease had refolded successfully from the inclusion bodies. Upon autocleavage of the expressed protease, the polyhistidine tag with additional amino acid residues appended to the N-terminus of the coding sequence is found to be removed accordingly. The protein expressed and purified by this new strategy possesses a molecular weight of approximately 28,000 in accord with the expected value for this venom protease. Further characterization of the recombinant protein employing a variety of techniques which include immunoblot analysis, RP-HPLC, ESI-MS, and N-terminal amino acid sequencing all shows indistinguishable properties to those of the isolated native protease. Most noteworthy is that the recombinant Tm-5 protease also exhibits amidase activity against N-benzoyl-Pro-Phe-Arg-p-nitroanilide, a unique and strict substrate for native Tm proteases reported previously.     

Molecular cloning and characterization of cDNA encoding fibrinolytic enzyme-3 from earthworm Eisenia foetida

Earthworm fibrinolytic enzyme (EFE), a multi-com-ponent protease purified from some earthworm breeds,belongs to serine protease family with fibrinolytic activity[1]. It has been used in prevention and treatment of cardiacand cerebrovascular diseases in Ch…     

Molecular cloning, sequencing, and expression of a fibrinolytic serine-protease gene from the earthworm Lumbricus rubellus

The full-length cDNA of the lumbrokinase fraction 6 (F6) protease gene of Lumbricus rubellus was amplified using an mRNA template, sequenced and expressed in E. coli cells. The F6 protease gene consisted of pro- and mature sequences by gene sequence analysis, and the protease was translated and modified into active mature polypeptide by N-terminal amino acid sequence analysis of the F6 protease. The pro-region of F6 protease consisted of the 44 residues from methionine-1 to lysine-44, and the mature polypeptide sequence (239 amino acid residues and one stop codon; 720 bp) started from isoleucine-45 and continued to the terminal residue. F6 protease gene clones having pro-mature sequence and mature sequence produced inclusion bodies in E. coli cells. When inclusion bodies were orally administrated rats, generated thrombus weight in the rat's venous was reduced by approximately 60 % versus controls. When the inclusion bodies were solubilized in pepsin and/or trypsin solutions, the solubilized enzymes showed hemolytic activity in vitro. It was concluded the F6 protease has hemolytic activity, and that it is composed of pro- and mature regions.