可溶性三聚化CD40-异亮氨酸拉链融合蛋白的制备及鉴定

以克隆的CD40cDNA为模板,经多步PCR构建羧基端融合异亮氨酸拉链(isoleucine zipper,IZ)三聚化基序和His6标签的可溶性CD40融合蛋白(sCD40IZ)的原核表达载体,在大肠杆菌中获得高效表达,分子量为27kD,与理论大小相符,表达产物主要存在于包涵体中,对包涵体蛋白进行稀释复性和纯化得到可溶性的sCD40IZ重组蛋白,该蛋白在溶液中的分子量为91kD,表明最有可能以三聚体形式存在。活性分析显示该蛋白能够与细胞上的CD40L结合,并且其结合活性与不含IZ基序的可溶性CD40相比明显提高。这些结果表明,在可溶性CD40羧基端融合IZ基序能够促进形成三聚体,并且具有增强的配基结合活性。     

Stability and folding of a mutant ribose-binding protein ofEscherichia coli

A mature mutant ribose-binding protein (RBP) ofEscherichia coli was obtained by site-directed mutagenesis, replacing Thr-3 in the N-domain of wild-type mature RBP (WT-mRBP) with a Trp residue (N-Trp-mRBP). The equilibrium unfolding properties and the refolding kinetics of this protein were monitored by fluorescence and circular dichroism (CD). The stability of N-Trp-mRBP appears to be the same as that of C-Trp-mRBP, another mutant obtained by replacing Phe-187 with a Trp, and lower than that of WT-mRBP. The overall refolding rate of N-Trp-mRBP is much smaller than that of C-Trp-mRBP, which, in turn, is similar to that of WT-mRBP. For the case of WT-mRBP, the rate constant obtained by Tyr fluorescence is identical to the value obtained by CD. But with C-Trp-mRBP, the rate constant from CD is smaller than the value from the Trp fluorescence and this difference in the rate constants is much greater with the N-TrpmRBP.     

Tyr61的芳香族侧链对稳定瘦素的结构至关重要

为了研究第61位Tyr（Tyr61）在瘦素（leptin）结构与功能中的作用,构建了2个瘦素突变体Y61F与Y61Q并对其进行了功能分析．Y61F突变体瘦素显示出与野生型瘦素相同的天然凝胶电泳迁移率及相似的折叠效率,而Y61Q突变体瘦素则显示出明显慢的电泳迁移率且较野生型瘦素更难于折叠．受体结合及免疫活性测定显示, Y61F突变体保留了野生型瘦素的大部分生物学活性,而Y61Q突变体仅保留了野生型瘦素16％的受体结合活性及30％的免疫活性．圆二色性分析及二级结构估算表明,Y61F突变体具有与野生型瘦素几乎一样的二级结构组成,而Y61Q突变体的结构则较野生型瘦素更为松散.本研究表明,Tyr61的芳香族侧链被包埋于分子内部的疏水区域中对稳定瘦素结构及其发挥生理功能至关重要,而Tyr61上的羟基在这一过程中并不起重要作用．     

Human parvovirus B19 virus-like particles: In vitro assembly and stability

Virus-like particles (VLPs) are biological nanoparticles identical to the natural virions, but without genetic material. VLPs are suitable for the analysis of viral infection mechanisms, vaccine production, tissue-specific drug delivery, and as biological nanomaterials. Human parvovirus B19 (B19) infects humans; therefore VLPs derived from this virus have enormous potential in medicine and diagnostics. Current production of self-assembled VLPs derived from B19 is typically carried out in eukaryotic expression systems. However many applications of VLPs require access to its internal core. Consequently, the processes of disassembly and further reassembly of VLPs are critical both for purification of viral proteins, and for encapsulation purposes. Herein we report the in vitro self-assembly of B19 VLPs derived from the recombinant VP2 protein expressed in Escherichia coli and the effects of pH and ionic strength on the assembly process. Our results demonstrate that VP2 is able to form VLPs completely in vitro. At neutral pH, homogeneous VLPs assemble, while at acidic and basic pHs, with low ionic strength, the major assemblies are small intermediates. The in vitro self-assembled VLPs are highly stable at 37 °C, and a significant fraction of particles remain assembled after 30 min at 80 °C.     

重组蛋白复性技术研究进展

本对近年来重组蛋白复性技术的研究进行了评述。比较分析了液相和固相复性的各种方法,提出了复性优化的方案,介绍了在化学复性基础上发展物理复性如高压复性法的新思路。     

人EGF受体L2结构域在大肠杆菌中表达、包涵体柱上复性及纯化

以PCR方法从克隆的EGFR胞外区cDNA中扩增编码EGFR-L2结构域的DNA片段,在其3′端加入编码His6标签的序列,与pET-3c连接构建EGFR-L2原核表达载体。该蛋白在大肠杆菌BL21(DE3)中获得高效表达,免疫印迹分析表明表达产物全部以包涵体形式存在,分步透析法和稀释法都不能获得可溶性复性产物,而Ni²⁺-NTA柱上复性法不仅能够获得可溶性的EGFR-L2蛋白,而且产物同时得到高度纯化,纯度>95％,复性的EGFR-L2与其配基EGF具有特异性的结合活性,但亲和力较低。这表明His6标签不但便于纯化目标蛋白,而且可利用Ni²⁺-NTA柱进行柱上复性,适用于不易通过常规方法复性的重组蛋白的制备。     

A7—B7二硫键缺失对胰岛素原重折叠及结构的影响

为研究A7 B7二硫键在胰岛素原结构和折叠中的作用 ,构建了A7 B7二硫键缺失的胰岛素原突变体 ,研究了其与野生型胰岛素原在体外重折叠产率、自由巯基氧化速度、CD谱、受体及抗体结合活性 ,以及对胰蛋白酶酶切敏感性的差别。结果表明 ,A7 B7二硫键缺失可导致胰岛素原α 螺旋明显减少以及对胰蛋白酶的酶切敏感性显著增加 ,其对胰岛素原结构的影响主要导致了受体结合活性的大幅度降低。突变体在体外重折叠 1h后巯基氧化速率较野生型明显减慢 ,但其最终折叠产率与野生型相当。由此提出一个胰岛素原折叠的可能途径 ,即A链链内二硫键最先形成 ,然后是两对链间二硫键。且A2 0 B19二硫键比A7 B7二硫键很可能先形成 ,在折叠中更重要。     

Human SLC26A4/Pendrin STAS domain is a nucleotide-binding protein: Refolding and characterization for structural studies

Mutations in the human SLC26A4/Pendrin polypeptide (hPDS) cause Pendred Syndrome /DFNB4, syndromic deafness with enlargement of the vestibular aqueduct and low-penetrance goiter. Here we present data on cloning, protein overexpression and purification, refolding, and biophysical characterization of the recombinant hPDS STAS domain lacking its intrinsic variable sequence (STAS-ΔIVS). We report a reproducible protein refolding protocol enabling milligram scale expression and purification of uniformly ¹⁵N- and ¹³C^/15N-enriched hPDS STAS-ΔIVS domain suitable for structural characterization by solution NMR. Circular dichroism, one-dimensional ¹H, two-dimensional ¹H–¹⁵N HSQC, and ¹H–¹³C HSQC NMR spectra confirmed the well-folded state of purified hPDS STAS-ΔIVS in solution. Heteronuclear NMR chemical shift perturbation of select STAS-ΔIVS residues by GDP was observed at fast-to-intermediate NMR time scales. Intrinsic tryptophan fluorescence quench experiments demonstrated GDP binding to hPDS STAS-ΔIVS with K_d of 178 μM. These results are useful for structure/function characterization of hPDS STAS, the cytoplasmic subdomain of the congenital deafness protein, pendrin, as well as for studies of other mammalian STAS domains.     

Crystal structure of human BACE2 in complex with a hydroxyethylamine transition-state inhibitor

BACE2 is a membrane-bound aspartic protease of the A1 family with a high level of sequence homology to BACE1. While BACE1 is involved in the generation of amyloid plaques in Alzheimer's disease by cleaving Abeta-peptides from the amyloid precursor protein, the physiological function of BACE2 is not well understood. BACE2 appears to be associated with the early onset of dementia in patients with Down's syndrome, and it has been shown to be highly expressed in breast cancers. Further, it may participate in the function of normal and abnormal processes of human muscle biology. Similar to other aspartic proteases, BACE2 is expressed as an inactive zymogen requiring the cleavage of its pro-sequence during the maturation process. We have produced mature BACE2 by expression of pro-BACE2 in Escherichia coli as inclusion bodies, followed by refolding and autocatalytic activation at pH 3.4. Using a C and N-terminally truncated BACE2 variant, we were able to crystallize and determine the crystal structure of mature BACE2 in complex with a hydroxyethylamine transition-state mimetic inhibitor at 3.1 angstroms resolution. The structure of BACE2 follows the general fold of A1 aspartic proteases. However, similar to BACE1, its C-terminal domain is significantly larger than that of the other family members. Furthermore, the structure of BACE2 reveals differences in the S3, S2, S1' and S2' active site substrate pockets as compared to BACE1, and allows, therefore, for a deeper understanding of the structural features that may facilitate the design of selective BACE1 or BACE2 inhibitors.     

Antiperoxidase antibodies enhance refolding of horseradish peroxidase

The effect of monoclonal antibodies on protein folding was studied using horseradish peroxidase refolding from guanidine hydrochloride as a model process. Among the five antiperoxidase clones tested, one was found to increase the yield of catalytically active peroxidase after guanidine treatment. The same clone also increased the activity of the native peroxidase by a factor of 2-2.5. While peroxidase refolding under standard conditions resulted in the recovery of only 7-8% of the initial catalytic activity, antibody-assisted refolding increased the yield to 50-100% (or 20-40% from the activity of native enzyme with antibodies). Kinetics of autorefolding and antibody-assisted refolding differed significantly. In the course of autorefolding the catalytic activity was recovered within the first 2.5 min and did not change further within a 2.5- to 60-min interval, whereas in the course of antibody-assisted refolding maximal catalytic activity was attained only in 60 min. The yield of active peroxidase for the antibody-assisted refolding depended linearly on the antibody concentration. The observed effect was strongly specific. Other antiperoxidase clones tested as well as nonspecific antithyroglobulin antibody affected neither kinetics, no the yield of peroxidase refolding.     

Refolding of protein inclusion bodies directly from E. coli homogenate using expanded bed adsorption chromatography

To avoid the intrinsic problem of aggregation associated with the traditional solution-phase refolding process, we proposed a solid-phase refolding method integrated with the expanded bed adsorption chromatography. The model protein was a fusion protein of recombinant human growth hormone and a glutathione S-transferase fragment. It was demonstrated that the inclusion body proteins in the cell homogenate could be directly refolded with higher yield. To verify the applicability of this method, we have tested with success three types of the starting materials, i.e., rhGH monomer, inclusion bodies containing the fusion protein, and the E. coli cell homogenate. This direct refolding process could reduce the number of the renaturation steps required and allow the refolding at a higher concentration, approximately 2 mg fusion protein per ml resin. This revised version was published online in July 2006 with corrections to the Cover Date.     

革兰氏阴性细菌β-桶状结构外膜蛋白体外折叠的研究进展

除了细胞质膜,革兰氏阴性细菌细胞还有一层组成细胞壁的外膜(Outer Membrane)。膜蛋白是外膜的主要组成成分之一,绝大多数外膜蛋白是由反向平行的β-折叠(β-Strands)通过相邻的氢键结合形成的β-桶状结构蛋白(β-Barrel Proteins)。这些蛋白既可作为通道蛋白、转运蛋白、酶、受体、毒力因子,也可作为结构蛋白发挥稳定外膜的重要作用,它们是否正确折叠并整合到外膜对革兰氏阴性细菌的生存至关重要。大多数外膜蛋白易于重组表达和体外重折叠(in vitro refolding),并且折叠状态可通过多种方法测定,因此β-桶状结构外膜蛋白被当着模式蛋白来研究各类生物和非生物因子对膜蛋白折叠的影响,是膜蛋白研究的一大热点。本文将从β-桶状结构外膜蛋白体外折叠的研究方法和影响折叠的因素角度对近年相关研究进展进行综合述评,最后总结了外膜蛋白体外折叠模式,并结合作者的相关研究结果和观点对该领域的研究前景进行了展望。