As a large family of hydrolases, GTPases are widespread in cells and play the very important biological function of hydrolyzing GTP into GDP and inorganic phosphate through binding with it. GTPases are involved in cell cycle regulation, protein synthesis, and protein transportation. Chaperones can facilitate the folding or refolding of nascent peptides and denatured proteins to their native states. However, chaperones do not occur in the native structures in which they can perform their normal biological functions. In the current study, the chaperone activity of the conserved GTPases of Escherichia coli is tested by the chemical denaturation and chaperone-assisted renaturation of citrate synthase and α-glucosidase. The effects of ribosomes and nucleotides on the chaperone activity are also examined. Our data indicate that these conserved GTPases have chaperone properties, and may be ancestral protein folding factors that have appeared before dedicated chaperones.
Citrate (si)-Synthase ; chemistry ; Cloning, Molecular ; Conserved Sequence ; Escherichia coli ; cytology ; enzymology ; GTP Phosphohydrolases ; chemistry ; genetics ; isolation & purification ; metabolism ; Guanosine Diphosphate ; pharmacology ; Guanosine Triphosphate ; analogs & derivatives ; pharmacology ; Molecular Chaperones ; chemistry ; genetics ; isolation & purification ; metabolism ; Protein Denaturation ; drug effects ; Protein Renaturation ; drug effects ; Ribosomes ; metabolism ; alpha-Glucosidases ; chemistry

Kv2.1 channel currents in pancreatic beta-cells are thought to contribute to action potential repolarization and thereby modulate insulin secretion. Because of its central role in this important physiological process, Kv2.1 channel is a promising target for the treatment of type 2 diabetes. Jingzhaotoxin-XI (JZTX-XI) is a novel peptide neurotoxin isolated from the venom of the spider Chilobrachys jingzhao. Two-microelectrode voltage clamp experiments had showed that the toxin inhibited Kv2.1 potassium currents expressed in Xenopus Laevis oocytes. In order to investigate the structure-function relationship of JZTX-XI, the natural toxin and a mutant of JZTX-XI in which Arg3 was replaced by Ala, were synthesized by solid-phase chemistry method with Fmoc-protected amino acids on the PS3 automated peptide synthesizer. Reverse-phase high performance liquid chromatography (RP-HPLC) and matrix assisted laser desorption/ ionization time-of-flight mass spectrometry (MALDI-TOF/TOF MS) were used to monitor the oxidative refolding process of synthetic linear peptides to find the optimal renaturation conditions of these toxins. The experiments also proved that the relative molecular masses of refolded peptides were in accordance with their theoretical molecular masses. RP-HPLC chromatogram of co-injected native and refolded JZTX-XI was a single peak. Under the whole-cell patch-clamp mode, JZTX-XI could completely inhibit hKv2.1 and hNav1.5 channels currents expressed in HEK293T cells with IC50 values of 95.8 nmol/L and 437.1 nmol/L respectively. The mutant R3A-JZTX-XI could also inhibit hKv2.1 and hNav1.5 channel currents expressed in HEK293T cells with IC50 values of 1.22 micromol/L and 1.96 micromol/L respectively. However, the prohibitive levels of R3A-JZTX-XI on hKv2.1 and hNav1.5 channels were reduced by about 12.7 times and 4.5 times respectively, indicating that Arg3 was a key amino acid residue relative to the hKv2.1 channel activity of JZTX-XI, but it is also an amino acid residue correlated with the binding activity of JZTX-XI to hNav1.5 channel. Our findings should be helpful to develop JZTX-XI into a molecular probe and drug candidate targeting to Kv2.1 potassium channel in the pancreas.
Animals ; HEK293 Cells ; Humans ; Insulin-Secreting Cells ; metabolism ; Mutant Proteins ; genetics ; pharmacology ; NAV1.5 Voltage-Gated Sodium Channel ; metabolism ; Neurotoxins ; chemical synthesis ; genetics ; pharmacology ; Protein Refolding ; Shab Potassium Channels ; antagonists & inhibitors ; metabolism ; Sodium Channel Blockers ; pharmacology ; Spider Venoms ; genetics ; pharmacology ; Transfection

To obtain the pure and soluble P51 antigen of HIV-1 strain CN54, we transformed the Escherichia. coli strain BL21 codonplus-RIL with recombinant plasmid pTHioHisA51 which carries a gene encoding the Polymerase (Pol) P51 antigen of HIV-1 CN54 formerly, and induced protein expression by IPTG. We purified the recombinant protein with Chelating Sepharose FF-Ni and DEAE-Sepharose FF column chromatography, then renatured the recombinant protein by dialyzation. Purified protein was identified by Western blotting. We labeled and coated antigen P51 in a dual-antigen sandwich system, and tested it with serum samples from HIV-infected individuals. The results showed that P51 was expressed as inclusion body, and represented about 50% of total cellular protein. After purification and renaturation, the purity of P51 was up to 95%. Western blotting and sandwich ELISA demonstrated that recombinant P51 had good anti-HIV antibody specificity and sensitivity. The results suggested that recombinant HIV-1 P51 can be prepared as diagnostic reagent, and provides valuable support for HIV-1 detection and vaccine research.
Escherichia coli ; genetics ; metabolism ; HIV Antibodies ; blood ; immunology ; HIV Infections ; immunology ; virology ; HIV Reverse Transcriptase ; biosynthesis ; genetics ; immunology ; HIV-1 ; classification ; immunology ; Humans ; Protein Renaturation ; Recombinant Proteins ; biosynthesis ; genetics ; immunology ; Sensitivity and Specificity

To establish a refolding process for the protein fused with 12-peptide of hirudin and reteplase (HV12p-rPA), we developed an anion-exchange chromatography assisted method to form correct disulfide bonds. After evaluating various parameters by orthogonal experiments with Q Sepharose XL as refolding medium, we found that urea gradient, sample loading size and L-Arg concentration were three major factors to affect the refolding outcomes, and urea gradient was critical to the recovery yield. Meanwhile, enzymatic activity of the refolded protein was decreased by the increase of sample loading size, and the optimal concentration of L-Arg in the eluting buffer was 1 mol/L. Thus, a dual-gradient of urea and pH on the anion-exchange chromatography resulted in remarkable increase of specific fibrinolytic and anti-coagulative activities of the refolded protein. Compared with the dilution method for refolding HV12p-rPA, the present approach was more effective and advantageous.
Chromatography, Ion Exchange ; methods ; Disulfides ; chemistry ; Fibrinolytic Agents ; analysis ; chemistry ; Hirudins ; analysis ; chemistry ; Protein Refolding ; Recombinant Fusion Proteins ; analysis ; chemistry ; Recombinant Proteins ; analysis ; chemistry ; Tissue Plasminogen Activator ; analysis ; chemistry

OBJECTIVETo establish a prediction method for the refolding of inclusion bodies and classify refolding types of different inclusion bodies directly from their primary structure to improve the efficiency of high throughput refolding process.

METHODSForty-three recombinant proteins performing important biological functions were expressed in E. coli. The probability of forming inclusion bodies of these proteins was predicted using Harrison's two parameter prediction model based on the proteins' amino acid composition. Subsequently, the proteins from the inclusion bodies were refolded using a double denaturation method that involved washing and denaturation in GdnHCl solution followed by denaturation in Urea solution and refolding through dilution.

RESULTSAll the proteins were detected in the form of inclusion bodies using SDS-PAGE method. The proteins were divided into two types according to the results of both solubility prediction and refolding experiments. Fourteen proteins were predicted to have the dependency of soluble expression. The refolding yields of these inclusion bodies were up to 70%. Twenty-nine proteins were predicted to have the high dependency of insoluble expression, and their refolding yields could be higher than 70% and lower than 60%. Comparison of the characteristics between the proteins with high and low refolding yields showed that the theoretical pI was significantly different (P<0.05).

CONCLUSIONSHarrison's two parameter prediction model has the value for potential application in classification of the inclusion bodies and prediction of solubility of proteins refolded from different inclusion bodies. This a novel method enhances the efficiency of high throughput refolding of inclusion bodies, and suggests that the theoretical pI of the proteins is an important parameter in the prediction of refolding yields.

Escherichia coli ; genetics ; metabolism ; Escherichia coli Proteins ; chemistry ; genetics ; Genetic Vectors ; genetics ; Inclusion Bodies ; chemistry ; Models, Biological ; Protein Refolding ; Recombinant Proteins ; biosynthesis ; genetics

Pulldown assay is an in vitro method for studies of protein-protein interactions, in which tagged proteins are usually expressed as the bait to enrich other proteins that could bind to them. In this technology, the GST tag is broadest used for its modest size and hydrophilic property. In most cases, the GST tag could increase the hydrophility of the fusion protein and help to avoid the formation of inclusion bodies. However, in the other few cases, the target protein may be strongly hydrophobic or have complicated structures that were hard to fold and assemble in correct conformations without champerons, and even the existence of GST tag could not make them soluble. These proteins were always expressed as inclusion bodies and had no functions. LMO2 was a small molecular weight and insoluble protein, in this study, GST system and MBP system were used to express GST-LMO2 and MBP-LMO2 fusion proteins, respectively. We found that GST-LMO2 fusion protein was expressed as inclusion bodies whereas MBP-LMO2 fusion protein was expressed in soluble form. Moreover, the production rate of MBP-LMO2 was also much higher than GST-LMO2. Then MBP-LMO2 fusion proteins and renatured GST-LMO2 fusion proteins were used as bait in pulldown assay to study the interaction between LMO2 and endogenous GATA1 in K562 cells. Western blot analyses showed that both of these proteins could bind to endogenous GATA1 in K562 cells, but recovered GATA1 protein by MBP-LMO2 fusion protein was much more than GST-LMO2 fusion protein. These results suggest that using of MBP system is a helpful attempt in the case of studying small molecular weight, strong hydrophobic proteins.
Adaptor Proteins, Signal Transducing ; Carrier Proteins ; chemistry ; Chemical Precipitation ; DNA-Binding Proteins ; chemistry ; GATA1 Transcription Factor ; chemistry ; Genetic Vectors ; Glutathione Transferase ; chemistry ; Humans ; K562 Cells ; LIM Domain Proteins ; Maltose-Binding Proteins ; Metalloproteins ; chemistry ; Protein Binding ; Protein Interaction Domains and Motifs ; Protein Renaturation ; Proto-Oncogene Proteins ; chemistry ; Recombinant Fusion Proteins ; genetics ; metabolism

OBJECTIVETo study the activities of interleukin (IL)-2 and granulocyte-macrophage colony-stimulating factor (GM-CSF) (hIL-2/mGM-CSF).

METHODSSOE PCR was used to change the linker of the fusion protein for higher activities. The fusion protein was expressed in Escherichia coli (E. coli) BL21 (DE3) in inclusion body (IB) form. After IB was extracted and clarified, it was denatured and purified by affinity chromatography. The protein was refolded by dilution in a L-arginine refolding buffer and refined by anion chromatography. The protein activity was detected by cytokine-dependent cell proliferation assay.

RESULTSThe expression of hIL-2/mGM-CSF in E. coli yielded approximately 20 mg protein /L culture and the purity was about 90%. The specific activities of IL-2 and GM-CSF were 5.4 x 10(6) IU/mg and 7.1 x 10(6) IU/mg, respectively.

CONCLUSIONThis research provides important information about the anti-tumor activity of hIL-2/mGM-CSF in vivo, thus facilitating future clinical research on hIL-2/mGM-CSF used in immune therapy.

Animals ; Arginine ; chemistry ; genetics ; metabolism ; Base Sequence ; Biological Assay ; Cell Proliferation ; Chromatography, Affinity ; Chromatography, Ion Exchange ; Cytokines ; metabolism ; Escherichia coli ; genetics ; Gene Expression ; Granulocyte-Macrophage Colony-Stimulating Factor ; chemistry ; genetics ; isolation & purification ; metabolism ; Humans ; Interleukin-2 ; chemistry ; genetics ; isolation & purification ; metabolism ; Mice ; Molecular Sequence Data ; Protein Folding ; Protein Renaturation ; Recombinant Fusion Proteins ; chemistry ; genetics ; isolation & purification ; metabolism

To obtain the recombinant 18 kD protein with high purity and normal bioactivity of Cysticercus cellulosae (rCE18), E. coli cells with the rCE18 were disrupted ultra-sonically, and the inclusion bodies were washed with a solution containing 0.2% deoxycholic acid sodium (DOC)and 2% DOC, respectively. Then they were denatured with 0.9% sodium lauroyl sarcosine (SKL) followed by dialysis and gel filtration to refold and purify the target protein. At the same time, this method was compared with GST-FF affinity chromatography and recovering from SDS-PAGE gel. Biological activity of purified rCE18 was analyzed with indirect ELISA, and the purity of the products was identified using SDS-PAGE. The purity of refolded inclusion bodies exceeded 60% and the total recovery of activated protein rCE18 was about 41.3%. The specificity of rCE18 reached up to 97.2% using indirect ELISA. An effective way for purifying and refolding rCE18 expressed in E. coli as inclusion bodies was established, rCE18 with higher purity and activity was obtained, which has the potential for developing diagnosis methods of porcine cysticercosis.
Animals ; Antigens, Helminth ; biosynthesis ; genetics ; immunology ; isolation & purification ; Chromatography, Gel ; Cysticercus ; genetics ; immunology ; metabolism ; Escherichia coli ; genetics ; metabolism ; Inclusion Bodies ; metabolism ; Protein Renaturation ; Recombinant Proteins ; genetics ; immunology ; isolation & purification

Nerve growth factor (NGF) promotes neuronal survival and differentiation and stimulates neurite outgrowth. NGF is synthesized as a precursor-proNGF in vivo. In this paper, a pET-proNGF prokaryocyte expression vector was constructed and transformed into E. coli BL21(DE3)pLysS. The proNGF was expressed in the form of non-active aggregated monomer in E. coli after induction with IPTG. SDS-PAGE revealed the proNGF expression product had a Mr.30.2 kD. Western blotting analysis showed that the protein had good antigenicity. Fusion protein was successfully purified by Ni2+-NTA affinity chromatography and cleaved by Enterokinase and 13.1 mg proNGF was obtained from 100 mL cell culture in a typical experiment. The protein was dialyzed in a redox system containing reduced and oxidized glutathione. RP-HPLC was used to analysis the result of the refolding. The refolded proNGF protein can induce neurite outgrowth of PC12 cells, which indicated that pro-form of NGF we obtained had biological activity.
Escherichia coli ; genetics ; metabolism ; Genetic Vectors ; genetics ; Humans ; Nerve Growth Factor ; biosynthesis ; genetics ; Protein Precursors ; biosynthesis ; genetics ; Protein Renaturation ; Recombinant Fusion Proteins ; biosynthesis ; genetics ; isolation & purification

Overexpression of recombinant Human Cu, Zn-Superoxide Dismutase (rhCu, Zn-SOD) in E. coli results in the form of insoluble inclusion body. Purity of rhSOD inclusion body was over 80% by isolation and purification. After preliminary renaturation by conventional dilution or dialysis, enzyme preparations was respectively purified by using Copper Metals-Chelating Affinity Chromatography (Copper-MCAC). RhSOD specific activity purified by MCAC (from the sample renatured partly by dialysis) was 2.2 times as much as that by dialysis and protein recovery was 64%. RhSOD specific activity purified by MCAC (from the sample renatured partly by dilution) was 5.3 times as much as that by dilution and protein recovery was 25%. The two rhSOD preparations purified by MCAC had specific activities about 5000 u/mg and activity recoveries were all over 130% of the enzyme activities in the samples renatured partly by dilution or dialysis. The above-mentioned results indicated that Copper-MCAC resulted in a purification and further renaturation of target protein. SDS-PAGE showed that the target protein rhSOD (19 kD) was purified homogeneously and NBT activity identification proved that the purified and renatured rhSOD had very strong SOD activity. In conclusion, Copper Metals-Chelaing Affinity Chromatography appears to be a simple, rapid and efficient procedure for purifying and further renaturing rhCu, Zn-SOD by dilution or dialysis. The method provided a new idea for purifying and renaturing recombinant proteins expressed in the form of inclusion body in E. coli.
Chelating Agents ; chemistry ; Chromatography, Affinity ; methods ; Escherichia coli ; genetics ; metabolism ; Humans ; Inclusion Bodies ; genetics ; Protein Renaturation ; Recombinant Proteins ; biosynthesis ; genetics ; isolation & purification ; Superoxide Dismutase ; biosynthesis ; genetics