中国南海新α芋螺毒素Mr1.8的合成及二硫键测定

目的:采用固相方法合成新型α4/7芋螺毒素Mr1.8(PECCTHPACHVSNPELC-NH2),并测定其折叠后的二硫键配对方式。方法:采用Fmoc-固相法合成线性肽Mr1.8,通过空气氧化折叠获得含二硫键的折叠产物,利用两步折叠法测定其二硫键连接方式。结果:Mr1.8线性肽经折叠生成2种产物Ⅰ和Ⅱ,质谱和二硫键分析结果显示Mr1.8-Ⅱ为正确折叠产物,其二硫键框架为(Cys1-Cys3,Cys2-Cys4)。结论:Mr1.8是一种新的α4/7型芋螺毒素,其一种主要折叠产物的二硫键框架为(Cys1-Cys3,Cys2-Cys4)。     

虎纹捕鸟蛛毒素Ⅴ的二硫键定位分析

虎纹捕鸟蛛毒素Ⅴ是从虎纹捕鸟蛛毒液中分离得到的一种昆虫毒素.它含有35个氨基酸残基,其中6个半胱氨酸形成三对二硫键.首先采用多酶将天然的肽链裂解后,通过MALDI-TOF质谱分析酶解肽段,推断出1对二硫键位于Cys9-Cys21,然后利用改进的部分还原分步测序法,确定虎纹捕鸟蛛毒素Ⅴ的另外2对二硫键的配对方式为Cys2-Cys16和Cys15-Cys28.因此,虎纹捕鸟蛛毒素Ⅴ的3对二硫键分别以Cys2-Cys16,Cys9-Cys21,Cys15-Cys28（即1-4、2-5和3-6）的方式配对.     

虎纹捕鸟蛛毒素V的二硫键定位分析

虎纹捕鸟蛛毒素V是从虎纹捕鸟蛛毒液中分离得到的一种昆虫毒素．它含有35个氨基酸残基,其中6个半胱氨酸形成三对二硫键．首先采用多酶将天然的肽链裂解后,通过MALDI-TOF质谱分析酶解肽段,推断出1对二硫键位于Cys9-Cys21,然后利用改进的部分还原分步测序法,确定虎纹捕鸟蛛毒素V的另外2对二硫键的配对方式为Cys2-Cysl6和Cys15-Cys28．因此,虎纹捕鸟蛛毒素V的3对二硫键分别以Cys2-Cys16,Cys9一Cys21,Cys15一Cys28(即1-4、2-5和3-6)的方式配对．     

玉米过氧化物还原蛋白BAS1的原核表达及其功能研究

植物过氧化物还原蛋白BAS1是巯基依赖的过氧化物酶,通过催化的Cys残基还原过氧化氢,依赖NADPH的叶绿体硫氧还蛋白还原酶保持BAS1的还原态。玉米含有两种BAS1:2-Cys PrxA和2-Cys PrxB。利用RT-PCR方法从玉米幼叶中克隆了编码成熟2-Cys PrxA的基因,并将蛋白Cys34残基突变成Ser34。SDS-PAGE显示纯化的野生型和突变体蛋白为一条主带,分子量约为23kDa;体外蛋白结合实验表明纯化的叶绿体硫氧还蛋白还原酶通过分子间二硫键结合纯化的2Cys PrxA的C34S突变体,非还原SDS-PAGE显示纯化的野生型2Cys PrxA含有分子间二硫键组成的二体,而纯化的C34S突变体呈现单体,巯基专一性标记化合物AMS修饰及活性分析表明纯化的BAS1还原态是催化还原过氧化氢所所必须的,它由硫氧还蛋白还原酶及其辅酶NADPH所催化。     

AUT凝胶电泳在牛胰核糖核酸酶折叠研究中的应用

目的:牛胰核糖核酸酶是一种用于蛋白折叠研究的经典模式蛋白,在折叠研究过程中主要使用高效液相色谱用于分离检测不同阶段的蛋白折叠中间体。高效液相色谱具有自动化、分离效果好、样品可回收等优点,同时也存在检测通量较低、仪器设备较为昂贵等不足。AUT凝胶电泳简便、快捷、检测通量较高,本文尝试将其应用于牛胰核糖核酸酶的折叠研究。方法:使用AUT凝胶电泳、酶活性检测、质谱对牛胰核糖核酸酶还原变性过程及产生的折叠中间体进行检测;通过高效液相色谱和质谱对折叠中间单体进行分离检测,并分别进行AUT凝胶电泳检测以解析各折叠中间单体在电泳中的条带位置;通过AUT凝胶电泳和酶切后质谱鉴定各折叠中间单体的二硫键配对方式。结果:AUT凝胶电泳可以有效区分不同条件下的牛胰核糖核酸酶还原变性过程,检测结果与酶活性、质谱结果相符,并可以很好地区分牛胰核糖核酸酶还原变性过程折叠中间体。高效液相色谱将牛胰核糖核酸酶还原变性过程折叠中间体分离为13个色谱峰,并与AUT凝胶电泳中的11个条带位置进行匹配。确认牛胰核糖核酸酶还原变性过程折叠中间单体的二硫键配对方式,并与AUT凝胶电泳条带进行匹配,Cys58-Cys110和Cys26-Cys84构象熵减作用强于Cys40-Cys95和Cys65-Cys72。结论:AUT凝胶电泳适用于检测牛胰核糖核酸酶折叠中间体,可以与高效液相色谱、质谱等检测技术相互补充,共同应用于牛胰核糖核酸酶的折叠研究。     

大肠杆菌二硫键形成蛋白A（DsbA）研究进展

二硫键形成蛋白A(DisulfidebondformationproteinA,DsbA)是存在于大肠杆菌周质胞腔内的一种参与新生蛋白质折叠过程中催化二硫键形成的折叠酶。综述了DsbA三维结构、进化过程、协助蛋白质体内外复性方面的研究进展。DsbA比硫氧还原蛋白具有更强的氧化性,其强氧化性来自于Cys30残基异常低的pKa值和不稳定的氧化型结构,通过定点突变的研究表明了Cys30残基是DsbA活性中心最关键的氨基酸残基之一。DsbA不论在体内与目标蛋白融合表达还是在体外以折叠酶形式添加,都能有效地催化蛋白质的折叠复性,同时DsbA还具有部分分子伴侣的活性。     

rhIL-12二硫键、N-糖基化位点及C端氨基酸序列分析

重组人白细胞介素12（rhIL-12）是一种已经用于治疗肿瘤,寄生虫、病毒性感染及造血障碍等疾病研究的异二聚体糖蛋白。结构确证是质量控制的重要内容,此研究对CHO细胞表达的rhIL-12二硫键配对方式、N-糖基化位点以及C端氨基酸序列进行了分析,使用Trypsin、Chymotrypsin和Glu-C三种酶分别对rhIL-12进行非还原酶解,尽可能地在其所有半胱氨酸残基之间断裂而形成二硫键相连的肽段,然后使用LC-MS/MS对酶解后的肽段样品进行分析,确定了rhIL-12样品中存在和理论配对方式相符的7对二硫键。将rhIL-12二硫键还原后并烷基化修饰保护,分别采用Trypsin,Chymotrypsin和GluC进行酶解,并用LC-MS/MS对酶解后肽段进行了质谱肽图及C端氨基酸序列分析,确定了rhIL-12 p35亚基C端氨基酸序列的8个氨基酸、p40亚基C端氨基酸序列的15个氨基酸。对rhIL-12样品还原及烷基化后用Trypsin变性酶解,所得肽段在H₂O及H₂¹⁸O水中分别用PNGase F糖苷酶处理酶切产物。并通过二级质谱分析脱糖后糖肽段分子量变化,从而确定了rhIL-12的3个N糖基化修饰位点,分别为p35亚基的71位和85位以及p40亚基的200位。通过建立酶解结合二级质谱鉴定的方法,证明了新药rhIL-12的二硫键位点、C端氨基酸序列和糖基化位点与理论一致。     

蛋白质组研究中肽质量指纹谱鉴定方法的建立及应用

建立了用肽质量指纹谱和数据库检索方法鉴定凝胶电泳分离蛋白南的方法。用标准蛋白质对胶上蛋白５质原位酶切制备肽谱的方法进行了讨论。分析了实际细胞蛋白质样品,获得双向电泳分离的人肺癌细胞蛋白质谱中三个蛋白质点的肽指纹谱。并通过数据７库检索分别鉴定为甘油醛－３－磷酸脱氢酶－２,测在蛋白羟基末端水解同工酶和丙糖磷酸异构酶。     

低压低氧延迟预适应小鼠海马差异表达蛋白的分离及鉴定研究

目的:探索低压低氧延迟预适应(HHDP)小鼠海马差异表达蛋白。方法:建立小鼠海马HHDP动物模型后,用含尿素的细胞裂解液提取海马总蛋白质。经等电聚焦、SDS-PAGE电泳、考马斯亮蓝R250染色,比较对照组及HHDP组双向电泳图谱上蛋白质点的差异。切取HHDP组表达增高的蛋白质点,经脱色、胰蛋白酶酶切、提取肽片段,进行MALDI-TOF-MS检测。结果:在正常对照组和HHDP组海马总蛋白双向电泳图谱上,分别检测到481±38和477±21个点,匹配点为169±6个。其中HHDP组比对照组增高大于2倍的有33±10个点,降低大于2倍的有21±12个点。电泳图谱平均相关系数为0.7748±0.0267。有12个点在HHDP组显著增高(P<0.05,n=4),对其进行了肽质量指纹图谱分析,其中8个蛋白点得到相应的肽质量指纹图谱。数据库检索显示其中一个为果糖二磷酸醛缩酶A。3个在蛋白质数据库中没有检索到与之相匹配的任何蛋白,可能为新蛋白。另外4个可找到与其有部分匹配的氨基酸序列,但分子量和等电点与对应蛋白相差悬殊,它们可能具有同源性。结论:小鼠海马HHDP时,果糖二磷酸醛缩酶A等多种蛋白表达发生改变,可能是产生HHDP的重要机制之一。     

重组单抗药物的肽图分析

建立了重组单抗药物的肽图分析方法。在变性条件下向抗体溶液加入还原剂,打开抗体内部所有交联的二硫键,再加入烷基化试剂封闭所有的自由巯基,使抗体分子在溶液中以游离伸展肽链的形式存在。加入胰蛋白酶,将充分伸展的肽链酶解成小的肽段。用反相高效液相色谱层析分析肽图谱。对连续3批中试产品及理化测定对照品进行肽图分析,各样品均能酶解完全,批间肽图谱一致。该方法实用有效,适于进行重组单抗等结构复杂的大分子蛋白药物的肽图检查分析。     

Predicting disulfide bond connectivity in proteins by correlated mutations analysis

MOTIVATION: Prediction of disulfide bond connectivity facilitates structural and functional annotation of proteins. Previous studies suggest that cysteines of a disulfide bond mutate in a correlated manner. RESULTS: We developed a method that analyzes correlated mutation patterns in multiple sequence alignments in order to predict disulfide bond connectivity. Proteins with known experimental structures and varying numbers of disulfide bonds, and that spanned various evolutionary distances, were aligned. We observed frequent variation of disulfide bond connectivity within members of the same protein families, and it was also observed that in 99% of the cases, cysteine pairs forming non-conserved disulfide bonds mutated in concert. Our data support the notion that substitution of a cysteine in a disulfide bond prompts the substitution of its cysteine partner and that oxidized cysteines appear in pairs. The method we developed predicts disulfide bond connectivity patterns with accuracies of 73, 69 and 61% for proteins with two, three and four disulfide bonds, respectively.     

Disulfide bond structures of IgG molecules: Structural variations,chemical modifications and possible impacts to stability and biological function

The disulfide bond structures established decades ago for immunoglobulins have been challenged by findings from extensive characterization of recombinant and human monoclonal IgG antibodies. Non-classical disulfide bond structure was first identified in IgG₄ and later in IgG₂ antibodies. Although, cysteine residues should be in the disulfide bonded states, free sulfhydryls have been detected in all subclasses of IgG antibodies. In addition, disulfide bonds are susceptible to chemical modifications, which can further generate structural variants such as IgG antibodies with trisulfide bond or thioether linkages. Trisulfide bond formation has also been observed for IgG of all subclasses. Degradation of disulfide bond through β-elimination generates free sulfhydryls disulfide and dehydroalanine. Further reaction between free sulfhydryl and dehydroalanine leads to the formation of a non-reducible cross-linked species. Hydrolysis of the dehydroalanine residue contributes substantially to antibody hinge region fragmentation. The effect of these disulfide bond variations on antibody structure, stability and biological function are discussed in this review.Key words: recombinant monoclonal antibody, disulfide bond, trisulfide bond, free sulfhydryl, dehydroalanine, thioether, aggregation     

Structure and function in rhodopsin: effects of disulfide cross-links in the cytoplasmic face of rhodopsin on transducin activation and phosphorylation by rhodopsin kinase.

Six rhodopsin mutants containing disulfide cross-links between different cytoplasmic regions were prepared: disulfide bond 1, between Cys65 (interhelical loop I-II) and Cys316 (end of helix VII); disulfide bond 2, between Cys246 (end of helix VI) and Cys312 (end of helix VII); disulfide bond 3, between Cys139 (end of helix III) and Cys248 (end of helix VI); disulfide bond 4, between Cys139 (end of helix III) and Cys250 (end of helix VI); disulfide bond 5, between Cys135 (end of helix III) and Cys250 (end of helix VI); and disulfide bond 6, between Cys245 (end of helix VI) and Cys338 (C-terminus). The effects of local restrictions caused by the cross-links on transducin (G(T)) activation and phosphorylation by rhodopsin kinase (RK) following illumination were studied. Disulfide bond 1 showed little effect on either G(T) activation or phosphorylation by RK, suggesting that the relative motion between interhelical loop I-II and helix VII is not crucial for recognition by G(T) or by RK. In contrast, disulfide bonds 2-5 abolished both G(T) activation and phosphorylation by RK. Disulfide bond 6 resulted in enhanced G(T) activation but abolished phosphorylation by RK, suggesting the structure recognized by G(T) was stabilized in this mutant by cross-linking of the C-terminus to the cytoplasmic end of helix VI. Thus, the consequences of the disulfide cross-links depended on the location of the restriction. In particular, relative motions of helix VI, with respect to both helices III and VII upon light activation, are required for recognition of rhodopsin by both G(T) and RK. Further, the conformational changes in the cytoplasmic face that are necessary for protein-protein interactions need not be cooperative, and may be segmental.     

Furin cleavage potentiates the membrane fusion-controlling intersubunit disulfide bond isomerization activity of leukemia virus Env

The membrane fusion protein of murine leukemia virus is a trimer of a disulfide-linked peripheral-transmembrane (SU-TM) subunit complex. The intersubunit disulfide bond is in SU linked to a disulfide bond isomerization motif, CXXC, with which the virus controls its fusion reaction (M. Wallin, M. Ekstr?m, and H. Garoff, EMBO J. 23:54-65, 2004). Upon receptor binding the isomerase rearranges the intersubunit disulfide bond into a disulfide bond isomer within the motif. This facilitates SU dissociation and fusion activation in the TM subunit. In the present study we have asked whether furin cleavage of the Env precursor potentiates the isomerase to be triggered. To this end we accumulated the late form of the precursor, gp90, in the cell by incubation in the presence of a furin-inhibiting peptide. The isomerization was done by NP-40 incubation or by a heat pulse under alkylation-free conditions. The cells were lysed in the presence of alkylator, and the precursor was immunoprecipitated, gel isolated, deglycosylated, and subjected to complete trypsin digestion. Disulfide-linked peptide complexes were separated by sodium dodecyl sulfate-tricine-polyacrylamide gel electrophoresis under nonreducing conditions. This assay revealed the size of the characteristic major disulfide-linked peptide complex that differentiates the two isomers of the disulfide bond between Cys336 (or Cys339) and Cys563, i.e., the bond corresponding to the intersubunit disulfide bond. The analyses showed that the isomerase was five- to eightfold more resistant to triggering in the precursor than in the mature, cleaved form. This suggests that the isomerase becomes potentiated for triggering by a structural change in Env that is induced by furin cleavage in the cell.     

Disulfide bond that constrains the HIV-1 gp120 V3 domain is cleaved by thioredoxin

A functional disulfide bond in both the HIV envelope glycoprotein, gp120, and its immune cell receptor, CD4, is involved in viral entry, and compounds that block cleavage of the disulfide bond in these proteins inhibit HIV entry and infection. The disulfide bonds in both proteins are cleaved at the cell surface by the small redox protein, thioredoxin. The target gp120 disulfide and its mechanism of cleavage were determined using a thioredoxin kinetic trapping mutant and mass spectrometry. A single disulfide bond was cleaved in isolated and cell surface gp120, but not the gp160 precursor, and the extent of the reaction was enhanced when gp120 was bound to CD4. The Cys(32) sulfur ion of thioredoxin attacks the Cys(296) sulfur ion of the gp120 V3 domain Cys(296)-Cys(331) disulfide bond, cleaving the bond. Considering that V3 sequences largely determine the chemokine receptor preference of HIV, we propose that cleavage of the V3 domain disulfide, which is facilitated by CD4 binding, regulates chemokine receptor binding. There are 20 possible disulfide bond configurations, and, notably, the V3 domain disulfide has the same unusual -RHStaple configuration as the functional disulfide bond cleaved in CD4.     

Bombyxin-II and its disulfide bond isomers: synthesis and activity.

Bombyxin-II, an insulin superfamily peptide of the silkmoth Bombyx mori, and its disulfide bond isomers have been synthesized by two ways of stepwise, semi-regioselective disulfide bond formation. The disulfide bond CysA20-CysB22 or CysA7-CysB10 was formed first, and then the two other disulfide bonds were formed by iodine oxidation. The conditions for the iodine oxidation were improved to suppress oxidative degradation of unprotected Trp residues. With these conditions, bombyxin-II was synthesized in high yields (26% and 32%). Its disulfide bond isomers were also obtained. Specific activity of the products indicates that the disulfide bond CysA20-CysB22 is important to the bombyxin activity.     

Biological regulation through protein disulfide bond cleavage

It is thought that disulfide bonds in secreted proteins are inert because of the oxidizing nature of the extracellular milieu. We have suggested that this is not necessarily the case and that certain secreted proteins contain one or more disulfide bonds that can be cleaved and that this cleavage is central to the protein's function. This review discusses disulfide bond cleavage in the secreted soluble protein, plasmin. Cleavage of plasmin disulfide bond(s) triggers peptide bond cleavage and formation of the tumour angiogenesis inhibitor, angiostatin. Tumour cells secrete phosphoglycerate kinase which facilitates cleavage of the plasmin disulfide bond(s). Phosphoglycerate kinase is not a conventional disulfide bond reductase. We propose that phosphoglycerate kinase facilitates cleavage of a particular plasmin disulfide bond by hydroxide ion, which results in formation of a sulfenic acid and a free thiol. The free thiol is then available to exchange with another nearby disulfide bond resulting in formation of a new disulfide and a new free thiol. The reduced plasmin is then susceptible to discreet proteolysis which results in release of angiostatin.     

A novel engineered interchain disulfide bond in the constant region enhances the thermostability of adalimumab Fab

We constructed a system for expressing the Fab of the therapeutic human monoclonal antibody adalimumab at a yield of 20 mg/L in the methylotrophic yeast Pichia pastoris. To examine the contribution of interchain disulfide bonds to conformational stability, we prepared adalimumab Fab from which the interchain disulfide bond at the C-terminal region at both the CH₁ and CL domains was deleted by substitution of Cys with Ala (Fab_ΔSS). DSC measurements showed that the Tm values of Fab_ΔSS were approximately 5 °C lower than those of wild-type Fab, suggesting that the interchain disulfide bond contributes to conformational thermostability. Using computer simulations, we designed a novel interchain disulfide bond outside the C-terminal region to increase the stability of Fab_ΔSS. The resulting Fab (mutSS Fab_ΔSS) had the mutations H:V177C and L:Q160C in Fab_ΔSS, confirming the formation of the disulfide bond between CH₁ and CL. The thermostability of mutSS Fab_ΔSS was approximately 5 °C higher than that of Fab_ΔSS. Therefore, the introduction of the designed interchain disulfide bond enhanced the thermostability of Fab_ΔSS and mitigated the destabilization caused by partial reduction of the interchain disulfide bond at the C-terminal region, which occurs in site-specific modification such as PEGylation.     

Identification and characterization of disulfide bonds in proteins and peptides from tandem MS data by use of the MassMatrix MS/MS search engine

A new database search algorithm has been developed to identify disulfide-linked peptides in tandem MS data sets. The algorithm is included in the newly developed tandem MS database search program, MassMatrix. The algorithm exploits the probabilistic scoring model in MassMatrix to achieve identification of disulfide bonds in proteins and peptides. Proteins and peptides with disulfide bonds can be identified with high confidence without chemical reduction or other derivatization. The approach was tested on peptide and protein standards with known disulfide bonds. All disulfide bonds in the standard set were identified by MassMatrix. The algorithm was further tested on bovine pancreatic ribonuclease A (RNaseA). The 4 native disulfide bonds in RNaseA were detected by MassMatrix with multiple validated peptide matches for each disulfide bond with high statistical scores. Fifteen nonnative disulfide bonds were also observed in the protein digest under basic conditions (pH = 8.0) due to disulfide bond interchange. After minimizing the disulfide bond interchange (pH = 6.0) during digestion, only one nonnative disulfide bond was observed. The MassMatrix algorithm offers an additional approach for the discovery of disulfide bond from tandem mass spectrometry data.     

Biological regulation through protein disulfide bond cleavage

Abstract

It is thought that disulfide bonds in secreted proteins are inert because of the oxidizing nature of the extracellular milieu. We have suggested that this is not necessarily the case and that certain secreted proteins contain one or more disulfide bonds that can be cleaved and that this cleavage is central to the protein's function. This review discusses disulfide bond cleavage in the secreted soluble protein, plasmin. Cleavage of plasmin disulfide bond(s) triggers peptide bond cleavage and formation of the tumour angiogenesis inhibitor, angiostatin. Tumour cells secrete phosphoglycerate kinase which facilitates cleavage of the plasmin disulfide bond(s). Phosphoglycerate kinase is not a conventional disulfide bond reductase. We propose that phosphoglycerate kinase facilitates cleavage of a particular plasmin disulfide bond by hydroxide ion, which results in formation of a sulfenic acid and a free thiol. The free thiol is then available to exchange with another nearby disulfide bond resulting in formation of a new disulfide and a new free thiol. The reduced plasmin is then susceptible to discreet proteolysis which results in release of angiostatin.