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。     

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。     

包含体蛋白质的复性研究进展

包含体的形成是异源蛋白质在大肠杆菌中高效表达的必然结果,也是目前产生重组蛋白质最有效的方法之一。不可溶、无生物活性的包含体必须经过变性、复性才能获得天然结构,完整特定的生物学功能。聚集是造成重组蛋白质复性产率低下的主要因素,因此理解蛋白质聚集机制,减少和防止聚集的发生是建立高效、高产率复性方法的关键。分子伴侣、低分子量添加物等在复性过程中的应用及新的复性方法的建立都大大提高了重组蛋白质复性产率。     

Kinetic model of lysozyme renaturation with the molecular chaperone GroEL

From the renaturation kinetics of denatured/reduced lysozyme assisted by the molecular chaperone GroEL, a simplified kinetic model was established based on the competition between protein folding and aggregation. In the presence of GroEL and ATP, the aggregate formation was a second order reaction. With 2 mM ATP, a renaturation yield of 90% at a high renaturation rate was obtained when the molar ratio of GroEL to lysozyme was 1:1.     

Production of a recombinant human basic fibroblast growth factor with a collagen binding domain

Summary Basic fibroblast growth factor (bFGF) is a potent in vitro mitogen for capillary endothelial cells, stimulates angiogenesis in vivo, and may participate in tissue repair. Basic FGF is found in abundance in tissues such as brain, kidney, and cartilage. This study reports the expression, purification, and renaturation of a biologically active human basic fibroblast growth factor fusion protein (hbFGF-Fl) fromEscherichia coli. A prokaryotic expression vector was engineered to produce a tripartite fusion protein consisting of a purification tag, a protease-sensitive linker and collagen binding domain, and a cDNA sequence encoding the active fragment of hbFGF. The expressed hbFGF-F1 and hbFGF-F2 (it contains the collagen binding domain), located in inclusion bodies, were solubilized with 6 M guanidine-HCl and renatured by a glutathione redox system and protracted dialysis under various experimental conditions. The purification of the recombinant proteins was achieved by binding the His-tag of the fusion protein on a nickel-nitrilotriacetic acid metal chelate column. The biological activity of the recombinant growth factor was demonstrated by its ability to stimulate proliferation of human vein endothelial cells, monitored by [³H]thymidine incorporation, where commercial recombinant human bFGF (rhbFGF) served as a positive control. Purified rhbFGF-F1 and rhbFGF-F2 constructs exhibited proliferative activity comparable to commercial rhbFGF. The high-affinity binding was demonstrated by the binding of [³H]collagen to the rhbFGF-F2 protein immobilized on a Ni-nitrilotriacetic acid column. The rhbFGF-F2 fusion protein bound to collagen-coated surfaces with high affinity. Taken together, these results demonstrate that biologically active rhbFGF fusion proteins can be recovered from transformed bacteria by oxidative refolding; thus, providing a means for their high-yield production, purification, and renaturation from microorganisms. Furthermore, we demonstrate that the auxiliary collagen binding domain effectively targets the recombinant growth factor to type 1 collagen. These studies advance the technology necessary to generate large quantities of targeted bFGF fusion proteins for specific biomedical applications.     

重组人睫状神经营养因子的复性研究

利用凝胶层析对人睫状神经营养因子原核基因工程产品进行复性研究,发现此方法的复性率高于稀释透析法.而且在复性的同时也进行了一步纯化工作.该方法简单、迅速、高效、重复性好,可用于规模生产.     

Isolation, renaturation, and formation of disulfide bonds of eukaryotic proteins expressed in Escherichia coli as inclusion bodies

Expression of recombinant proteins in Escherichia coli often results in the formation of insoluble inclusion bodies, In case of expression of eukaryotic proteins containing cysteine, which may form disulfide bonds in the native active protein, often nonnative inter- and intramolecular disulfide bonds exist in the inclusion bodies. Hence, several methods have been developed to isolate recombinant eukaryotic polypeptides from inclusion bodies, and to generate native disulfide bonds, to get active proteins. This article summarizes the different steps and methods of isolation and renaturation of eukaryotic proteins containing disulfide bonds, which have been expressed in E. coli as inclusion bodies, and shows which methods originally developed for studying the folding mechanism of naturally occurring proteins have been successfully adapted for reactivation of recombinant eukaryotic proteins. (c) 1993 John Wiley & Sons, Inc.     

Sequence specificity of cytosine methylation in the DNA of the Chinese hamster ovary (CHO-K1) cell line

We have determined the DNA renaturation kinetics for those DNA sequences of the Chinese hamster ovary (CHO-K1) cells in which enzymatic cytosine methylation occurred immediately after strand synthesis and for those in which methylation was delayed after strand synthesis. DNA sequences showing immediate or delayed methylation were found to be distributed throughout all repetition classes of the DNA of these cells, with a slight concentration of immediate methylation in moderately repetitive sequences and with delayed methylation being slightly over-represented in the highly repetitive fraction. However, DNA sequences showing both classes of methylation were represented equally in unique DNA sequences. We interpret these data to mean that the methylase acting near the replication forks (the ‘immediate’ methylase) is a relatively inefficient enzyme, missing some 20% of hemimethylated sites produced by DNA replication in these cells. We suggest that the methylase performing maintenance methylation at sites remote from the replication forks (the ‘delayed’ methylase) is simply a back-up enzyme for the first and that it has no true sequence specificity. The implications of this for the function(s) of DNA methylation in mammalian cells are discussed.     

Two-dimensional zymogram analysis of nucleases in Bacillus subtilis

A two-dimensional zymogram procedure for the analysis of nucleases is described. Isoelectric focusing (IEF) and nonequilibrium pH gradient electrophoresis (NEPHGE) were compared as first dimensions in combination with sodium dodecyl sulfate (SDS) electrophoresis as the second dimension in analyzing nucleases in lysates of Bacillus subtilis. All renaturable nucleases detected following SDS electrophoresis alone were resolved in NEPHGE-SDS electrophoresis gels whereas, in IEF gels, most either were at the basic end or were not present in the second-dimension gels. This method of analysis has revealed a complexity in nuclease species in B. subtilis not previously recognized. Eighty-three discreet nuclease activities have been detected in B. subtilis lysates. Using purified deoxyribonuclease I (bovine pancreas), as little as 10 pg of nuclease can be detected.     

Unfolding and refolding of hen egg-white riboflavin binding protein

The unfolding and refolding of riboflavin-binding protein (RfBP) from hen egg-white induced by addition of guanidinium chloride (GdnHCl), and its subsequent removal by dialysis have been studied by c.d. and fluorescence for both the native and reduced protein. The reduction of its nine disulphide bonds causes a reduction in the secondary structure (alpha-helix plus beta-sheet) from 63% to 33% of the amino acid residues. Unfolding of the native protein occurred in two phases; the first involving a substantial loss of tertiary structure, followed by a second phase involving loss of secondary structure at higher GdnHCl concentrations. By contrast this biphasic behaviour was not discernible in the reduced protein. The loss of ability to bind riboflavin occurred after the first phase of unfolding. Comparison of unfolding of the holoprotein and apoprotein suggested that riboflavin has only a small stabilizing effect on the unfolding process. After removal of GdnHCl, the holoprotein, apoprotein and reduced protein assumed their original conformation. The significance of the results in relation to various models for protein folding is discussed.