Purification and Refolding of a Novel β-Agarase from Inclusion Body of E. coli

β-agarase AgaB appears to represent a new family of glycoside hydrolase; it is structurally and functionally different from other known agarases. In the present study, AgaB was expressed with a temperature-inducible expression system in E. coli BL21 (DE3) as a fusion protein bearing a C-terminal hexahistidine tag. The protein existed mainly in the form of inclusion body. After being washed and solubilized, AgaB in inclusion body was denatured and purified to electrophoretic purity by immobilized metal affinity chromatography. The purified AgaB was then refolded using a simple pulse dilution method, and the refolded AgaB showed a high specific hydrolysis activity of about 1600 units /mg protein. Forty milligrams of refolded pure protein were obtained from 1L of culture.

Efficient Protein Refolding Using Surfactants at High Final Protein Concentration

The refolding of denatured hen egg white lysozyme (HEWL) was examined by surfactants at a high final refolded HEWL concentration (1 mg/mL). Hexadecyltrimethylammonium bromide (CTAB) and sucrose fatty acid monoester (DK-SS) were used to dissolve denatured HEWL without denaturants such as guanidine hydrochloride (GuHCl) and urea. When denatured HEWL was perfectly dissolved in buffer solutions containing surfactants and dithiothreitol (DTT), the concentration of CTAB was about one-twentieth times less than that of DK-SS. The concentration of CTAB strongly affected the refolding yield, and the maximum refolding yield was obtained at 0.88 mM CTAB, which is around the critical micelle concentration of CTAB. The refolding yield was influenced by the molar ratio of oxidized glutathione (GSSG) to DTT, and the maximum refolding yield was obtained when [GSSG]/[DTT] was 1.5. The refolding yield was markedly dependent upon the solution pH of HEWL, and exhibited 80% at pH 5.2.

Microwave based reversible unfolding and refolding of alcohol oxidase protein probed by fluorescence and circular dichroism spectroscopy

The reversible effect of microwave mediated denaturation of protein at low exposure time of 10 s has been demonstrated for the first time. The effect of microwave (2.45 GHz and 900 W) was confirmed in a homo-octameric alcohol oxidase in aqueous solution of pH 7.5. The unfolding events did not transverse through any intermediate states and no subunits of the protein were detached during the process. The refolding of the protein achieved at 4℃ for 24 h had regenerated the native enzyme. This reversible refolding approach excludes any chemical reagent and therefore established as simple technique for protein unfolding-folding studies.

Evidence for the Existence of Cross-Linked Intermediates during Unfolding and Refolding of CK in UGGE

Urea gradient gel electrophoresis (UGGE) is an important technique for studying the conformation changes of proteins during denaturation. This paper reports on an investigation of the unfolding and refolding of creatine kinase (CK) by UGGE. The native and denatured CK underwent electrophoresis in polyacrylamide gels containing a linear 08 mol/L gradient of urea perpendicular to the direction of migration. The results showed that unfolding and refolding of CK is a relatively rapid process. The denatured enzyme could refold to a conformation with activity during electrophoresis at low urea concentrations, indicating that denaturation in urea is reversible. More importantly, both the native and denatured CK were separated into multiple parallel bands through UGGE, but the bands decreased significantly when mercaptoethanol was added to the samples. The results suggest that various kinds of unfolding and refolding intermediates were formed during UGGE, which are assumed to be oligomers with disulfide bonds between peptide chains. Urea/SDS (sodium dodecylsulphate) polyacrylamide two dimensional electrophoresis proved that these unfolding and refolding intermediates formed during UGGE were oligomers which were composed of different number of subunits cross linked by disulfide bonds. The results indicate that the unfolding and refolding of CK are relatively rapid processes with some cross linked intermediates with disulfide bonds during unfolding and refolding of the enzyme.

In vitro insulin refolding:Characterization of the intermediates and the putative folding pathway

The in vitro refolding process of the double-chain insulin was studied based on the investigation of in vitro single-chain insulin refolding. Six major folding intermediates, named P1A, P2B, P3A, P4B, P5B, and P6B, were captured during the folding process. The refolding experiments indicate that all of these intermediates are on-pathway. Based on these intermediates and the formation of hypothetic transients, we propose a two-stage folding pathway of insulin. (1) At the early stage of the folding process, the reduced A chain and B chain individually formed the intermediates: two A chain intermediates (P1A and P3A), and four B chain intermediates (P2B, P4B, P5B, and P6B). (2) In the subsequent folding process, transient I was formed from P3A through thiol/disulfide exchange reaction; then, transients II and III, each containing two native disulfides, were formed through the recognition and interaction of transient I with P4B or P6B and the thiol group's oxidation reaction mainly using GSSG as oxidative reagent; finally, transients II and III, through thiol/mixture disulfide exchange reaction, formed the third native disulfide of insulin to complete the folding.

Refolding of OPTA-labeled creatine kinase denatured by guanidinium chloride

Although refolding of fully denatured protein molecules in vitro is not a valid model of folding of the nascent peptide chain in a biologically active protein in vivo, it can provide some useful information for protein folding. Therefore, refolding of denatured proteins has been extensively studied in recent years. It has been previously reported that during the refolding of guanidine or urea denatured creatine kinase, the enzymatic activity and the na-

Effects of Glycerol in the Refolding and Unfolding of Creatine Kinase

The effects of glycerol in the refolding, reactivation, unfolding, and inactivation of guanidine denatured creatine kinase were studied by observing the fluorescence emission spectra and the circular dichroism spectra, and by recovery and inactivation of enzymatic activity and aggregation. The results show that low concentrations of glycerol (<25%) improve the refolding yields of creatine kinase, but high glycerol concentrations decrease its recovery. Glycerol favors the secondary structural formation and inhibits aggregation of creatine kinase as proline does. These systematic observations further support the suggestion that low concentrations of glycerol possibly play a chaperone role in the refolding of creatine kinase. In addition, glycerol reduces the inactivation and unfolding rate of creatine kinase, increases the change in transition free energy of unfolding (ΔΔG u) and stabilizes its active conformation relative to the partially unfolded state with no glycerol. In the presence of glycerol, the inactivation and unfolding dynamics of creatine kinase are related to glycerol concentrations. Glycerol blocks the exposure of hydrophobic areas and the dissociation of dimers, and protects creatine kinase against guanidine denaturation in a concentration dependent manner. This study suggests that glycerol as an energy substrate for metabolism and organic components in vivo, assists correct protein folding, maintains adequate rates of enzymatic catalysis and stabilizes the protein secondary and tertiary conformations.

Heterologous expression,refolding,and characterization of a calcium-independent phospholipase A1 from Streptomyces albidoflavus

Phospholipase A1(PLA_(1))is a member of the hydrolase family with applications in various fields,especially in the food industry.A calcium-independent PLA_(1) from Streptomyces albidoflavus was expressed in E.coli BL21(DE3)in this study.The results indicated that the soluble expression of PLA_(1) was at low level,which was possibly due to the toxicity of PLA_(1) to the host.In contrast,the expression of the enzyme as inclusion bodies exhibited a high-level expression and 0.3 mg inclusion bodies protein could be derived from 1 mL culture medium.Furthermore,the renaturation of PLA_(1) was achieved through a direct dilution method,yielding 29.6 U/mL PLA_(1) activity after 16 h of renaturation at 4℃.For improving the efficiency of the dilution refolding process,a continuous refolding strategy was established,and 155 U/mL PLA_(1) activity was derived from the continuous refolding process.With soybean lecithin as the substrate,the specific activity of purified renatured PLA_(1) was 1380 U/mg and the optimal temperature and pH was found to be 60℃ and 6.5.In addition,the renatured PLA_(1) was observed with better activity towards phosphatidyl inositol,whilst lipase activity was detected when the catalyzing temperature was below 55℃.Overall,this study provides a possible solution to obtain calcium-independent PLA_(1) with high yield by heterologous expression in E.coli and hence to promote its further application in the field of food industry.

Profiling neuroprotective potential of trehalose in animal models of neurodegenerative diseases:a systematic review

Trehalose,a unique nonreducing crystalline disaccharide,is a potential disease-modifying treatment for neurodegenerative diseases associated with protein misfolding and aggregation due to aging,intrinsic mutations,or autophagy dysregulation.This systematic review summarizes the effects of trehalose on its underlying mechanisms in animal models of selected neurodegenerative disorders(tau pathology,synucleinopathy,polyglutamine tract,and motor neuron diseases).All animal studies on neurodegenerative diseases treated with trehalose published in Medline(accessed via EBSCOhost)and Scopus were considered.Of the 2259 studies screened,29 met the eligibility criteria.According to the SYstematic Review Center for Laboratory Animal Experiment(SYRCLE)risk of bias tool,we reported 22 out of 29 studies with a high risk of bias.The present findings support the purported role of trehalose in autophagic flux and protein refolding.This review identified several other lesser-known pathways,including modifying amyloid precursor protein processing,inhibition of reactive gliosis,the integrity of the blood-brain barrier,activation of growth factors,upregulation of the downstream antioxidant signaling pathway,and protection against mitochondrial defects.The absence of adverse events and improvements in the outcome parameters were observed in some studies,which supports the transition to human clinical trials.It is possible to conclude that trehalose exerts its neuroprotective effects through both direct and indirect pathways.However,heterogeneous methodologies and outcome measures across the studies rendered it impossible to derive a definitive conclusion.Translational studies on trehalose would need to clarify three important questions:1)bioavailability with oral administration,2)optimal time window to confer neuroprotective benefits,and 3)optimal dosage to confer neuroprotection.

可溶性人TRAIL分子的制备及其抗肿瘤活性

The cDNA encoding human TRAIL extracellular region(amino acids 41—281) was amplified by reverse transcription(RT) PCR from total RNA derived from human acute promyelocytic leukemia cell line HL 60. After sequencing, the cDNA was cloned into the vector pQE 80L and transformed into E.coli DH5 α . By IPTG induction, the soluble TRAIL 41—281 (sTRAIL 41—281 ) protein was expressed with the 40% of total bacteria protein. Inclusion bodies were dissolved into 8 mol/L urea, purified by Ni NTA chromatography column, the product with over 90% purity was obtained. After refolding by dialysis, the active trimer form of sTRAIL 41～281 was derived from the renatured proteins by gel filtration chromatography. The MTT assay, flow cytometry and DNA fragmentation assay showed that the refolded sTRAIL 41～281 could potently inhibit the growth of Jurkat cells and induce apoptosis, confirmed the apoptosis inducing activity of sTRAIL 41～281 on tumor cells, it will benefit the further research of TRAIL.

Increase in thermal stability of proteins adsorbed on biomass charcoal powder prepared from plant biomass wastes

Thermal stability of lysozyme adsorbed on biomass charcoal powder (BCP), which was prepared from plant biomass wastes such as dumped adzuki bean, bamboo, and wood by pyrolysis without combustion under nitrogen atmosphere and comminution with a jet mill, was examined. Adsorbing lysozyme on BCP could sufficiently prevent proteins from denaturing and aggregating in an aqueous solution at high temperatures, and enhanced the refolding of thermally denatured proteins by cooling treatment. The remaining activities of lysozyme adsorbed on BCP of adzuki bean exhibited 51% by cooling treatment after the heat treatment at 90?C for 30 min, although that of native lysozyme was almost lost under the same experimental conditions. The thermostabilization effect of BCP on the remaining activity of adsorbed lysozyme was markedly dependent upon the kind of plant biomass wastes.

Cloning, purification and characterization of the ribosomal protein L11 from E. coli

A high-expression system of L11 was constructed and investigated its interaction with other elements of the ribosome using physicochemical methods. The gene rplK, coding for the protein L11 from the E. coli 50S ribosomal subunit was amplifyied, cloned and over-expressed. The protein L11 was purified under native and denaturing conditions, refolded and the structure of both proteins was compared. The protein L11 properly refolded from 6M urea after dialysis. Experiments on binding of proteins L11, RRF and EF-G from Escherichia coli were performed by ana-lytical centrifugation and Biacore. Specific binding between protein L11 and RRF by analytical cen-trifugation was not detected probably due to struc-tural reasons. These findings may be helpful in the design of new antibiotics that specifically disrupt the interactions in the “GTP-associated site” of the bac-terial ribosome, as many of them are not effective anymore. A common intrinsically disordered region of protein L11 was found to be the amino acid se-quence 86-97, while the residues 67-74, containing the linker region, are predicted to be disordered by DisEMBL.

Disassembly intermediates of RbsD protein remain oligomeric despite the loss of an intact secondary structure

Many proteins exist as homo-oligomers in living organisms wherein the change of oligomeric status apparently serves as an effective means for modulating their biological activities. We have previously reported that the homo-decameric RbsD from Escherichia coli undergoes stepwise disassembly and non-stepwise reassembly. Here the structural status of the urea-induced RbsD disassembly intermediates was examined, mainly using urea-containing polyacrylamide gel electrophoresis and chemical cross-linking. Such intermediates were found to remain oligomeric while losing their intact secondary structures. Such disassembly intermediates were able to effectively refold when the concentration of the urea denaturant was reduced to a lower level, or to refold/reassemble into the native decamers when urea was completely removed, as detected by non-denaturing polyacrylamide gel electrophoresis. These novel observations strongly suggest that the assembly of oligomeric proteins may occur before the completion of subunit folding.

TOTAL SYNTHESIS OF Trichosanthes TRYPSIN INHIBITOR AND ITS ANALOGUE

Trichosanthes trypsin inhibitor (TTI) is a peptide consisting of 27 amino acid residues with three pairs of disulfide bonds. This paper reports the total synthesis and disulfide bond refolding of this inhibitor and its analogue. After purification, the amino acid sequence and stoichiometrical inhibitory activity against trypsin of the synthetic inhibitor were compatible with those of the natural inhibitor. The analogue of this inhibitor in which residue Met in position 6 was replaced by Ala was also synthesized. The antitrypsin activity of this synthetic analogue was also approximate to that of the natural inhibitor.

Function of disulflde bond Cys45-Cys50 of prochymosin

The conditions (temperature, time, pH) for solubilizing inclusion bodies of prochymosin mutant, Cys45Asp/Cys50Ser, are identical with those for the wild type. Moreover, they have similar oxidative refolding behavior. Under the same renaturation conditions both of them can undergo correct refolding leading to the formation of activable molecules. This is quite different from the mutant with deletion of Cys250-Cys283, indicating that Cys45-Cys50 contributes less to the correct refolding of prochymosin than Cys250- Cys283. However, deletion of Cys45-Cys50 results in a remarkable decrease of the thermostability of pseudochymosin, suggesting that this disulfide bond plays an important role in stabilizing enzyme conformation. The proteolytic (P) and milk-dotting (C) activities of the mutant of pseudochymosin, Cys45Asp/Cys50Ser, are lower than those of its wild counterpart. The C/P ratio of the former is onefold higher than that of the latter.

The thermodynamic stability of insulin disulfides is not affected by the C-domain of insulin-like growth factor 1

Both Insulin and insulin-like growth factor 1 are members of insulin superfamily. They share homologous primary and tertiary structure as well as weakly overlapping biological activity. However, their folding behavior is different: insulin and its recombinant precursor (PIP) fold into one unique tertiary structure, while IGF-1 folds into two disulfides isomers with similar thermodynamic stability. To elucidate the molecular mechanism of their different folding behavior, we prepared a single-chain hybrid of insulin and IGF-1, [B10Glu]Ins/IGF-1(C), and studied its folding behavior compared with that of PIP and IGF-1. We also separated a major non-native disulfides isomer of the hybrid and studied its refolding. The data showed that the C-domain of IGF-1 did not affect the folding thermodynamics of insulin, that is, the primary structure of the hybrid encoded only one thermodynamically stable disulfides linkage. However, the folding kinetics of insulin was affected by the C-domain of IGF-1.

Mung Bean Trypsin Inhibitor——Synthesis of a Fragment and Its Analogues

The Lys active fragment of the mung bean trypsin inhibitor is composed of two peptidechains,one with 26 amino acid residues and the other with 9 residues linked by two interdisulfide bonds.The two peptide chains could be separated successfully from each other by reduction.with DTT followedby gel filtration.The reduced long peptide chain containing 6 Cys residues was subjected to air oxidation,and about 25% of the original antitrypsin activity of the Lys fragment was recovered.Following the previ-ously reported sequence,the solid-phase synthesis of this long peptide chain and its disulfide bond refold-ing are presented.Unexpectedly,the synthetic peptide showed much lower antitrypsin activity than thenatural one after reduction and air reoxidation.In order to explain this uncompatible result,we redeter-mined the sequence of the native long peptide chain of the Lys active fragment and obtained the result thatthe P′2 position is Ile instead of Lys as previously reported.To ascertain the correct sequence,we synthe-sized another 22-peptide following the newly determined 26-peptide sequence,and skimming two residuesrespectively from N-terminus and C-terminus.After reduction and reoxidation,the synthetic 22-peptidehad the same antitrypsin activity as that of the native 26-peptide.Meanwhile,an analogue of this 22-pep-tide in which the residue Lys at the reactive site was replaced by Ala was also synthesized.This syntheticanalogue did not show any activity either to trypsin or to elastase.

Effect of ligand structure of stationary phase of high performance hydrophobic interaction chromatography on renaturation efficiency of GuHCl-denaturedα-chymotrypsin

The renaturation of the denatured α-chymotrypsin (α-Chy) with 1.7 mol · L-1 guanidine hydrochloride (GuHCI) by three kinds of stationary phase of high performance hydrophobic interaction chromatography (STHIC) with a comparable hydrophobicity but different ligand structures was investigated. The obtained result indicates that the ligand structures of the three STHIC contribute to the renaturation efficiency of α-Chy in the order of the end ligands PEG-600＜ phenyl group ＜ tetrahydrofurfuryl alcohol (THFA).

Cause of Irreversible Inactivation of Aminoacylase in Urea Solution

Some have suggested that the refolding of denatured aminoacylase is difficult. The present study reports that aminoacylase denatured in urea concentrations more than 4?mol/L was markedly but partially unfolded and could be reactivated and refolded very rapidly. However, the extent of reactivation decreased with increasing time suggesting an irreversible inactivation occurred in a biphasic course. The fast phase of the irreversible inactivation is suggested to accompany the unfolding. Oxidation of the thiol groups exposed by unfolding may be one of the main causes of the second phase of the irreversible inactivation.