The effects of lauryl maltoside on the reactivation of several enzymes after treatment with guanidinium chloride

Surfactant-Amino Acid and Surfactant-Surfactant Interactions in Aqueous Medium: a Review

An overview of surfactant-amino acid interactions mainly in aqueous medium has been discussed. Main emphasis has been on the solution thermodynamics and solute-solvent interactions. Almost all available data on the topic has been presented in a lucid and simple way. Conventional surfactants have been discussed as amphiphiles forming micelles and amino acids as additives and their effect on the various physicochemical properties of these conventional surfactants. Surfactant-surfactant interactions in aqueous medium, various mixed surfactant models, are also highlighted to assess their interactions in aqueous medium. Finally, their applied part has been taken into consideration to interpret their possible uses.

Effects of monopropanediamino-β-cyclodextrin on the denaturation process of the hybrid protein BlaPChBD

Irreversible accumulation of protein aggregates represents an important problem both in vivo and in vitro. The aggregation of proteins is of critical importance in a wide variety of biomedical situations, ranging from diseases (such as Alzheimer's and Parkinson's diseases) to the production (e.g. inclusion bodies), stability, storage and delivery of protein drugs. β-Cyclodextrin (β-CD) is a circular heptasaccharide characterized by a hydrophilic exterior and a hydrophobic interior ring structure. In this research, we studied the effects of a chemically modified β-CD (BCD07056), on the aggregating and refolding properties of BlaPChBD, a hybrid protein obtained by inserting the chitin binding domain of the human macrophage chitotriosidase into the class A β-lactamase BlaP from Bacillus licheniformis 749/I during its thermal denaturation. The results show that BCD07056 strongly increases the refolding yield of BlaPChBD after thermal denaturation and constitutes an excellent additive to stabilize the protein over time at room temperature. Our data suggest that BCD07056 acts early in the denaturation process by preventing the formation of an intermediate which leads to an aggregated state. Finally, the role of β-CD derivatives on the stability of proteins is discussed.

Molecular dynamics for surfactant-assisted protein refolding

Surfactants are widely used to refold recombinant proteins that are produced as inclusion bodies in E. Coli. However, the microscopic details of the surfactant-assisted protein refolding processes are yet to be uncovered. In the present work, the authors aim to provide insights into the effect of hydrophobic interactions of a denatured protein with surfactant molecules on the refolding kinetics and equilibrium by using the Langevin dynamics for coarse-grained models. The authors have investigated the folding behavior of a beta-barrel protein in the presence of surfactants of different hydrophobicities and concentrations. It is shown that the protein folding process follows a "collapse-rearrangement" mechanism, i.e., the denatured protein first falls into a collapsed state before acquiring the native conformation. In comparison with the protein folding without surfactants, the protein-surfactant hydrophobic interactions promote the collapse of a denatured protein and, consequently, the formation of a hydrophobic core. However, the surfactants must be released from the hydrophobic core during the rearrangement step, in which the native conformation is formed. The simulation results can be qualitatively reproduced by experiments.

Assisting the reactivation of guanidine hydrochloride-denatured aminoacylase by hydroxypropyl cyclodextrins

Cyclodextrin is a water-soluble circular oligosaccharide with a cylinder shape characterized by exterior hydrophilic rims and an interior hydrophobic cavity, which makes it an ideal additive to prevent proteins from aggregating during refolding. In this research, three hydroxypropyl cyclodextrins (HPCDs), HP-alpha-, beta-, and gamma-CD, were used to investigate the molecular mechanism of their effects on assisting aminoacylase refolding. The aggregation and reactivation experiments suggested that at moderate concentrations, HPCDs could suppress aggregation and assist aminoacylase refolding in a concentration-dependent manner, and HP-beta-CD was the most efficient of the three HPCDs. Low concentrations of HP-alpha-CD and high concentrations of HP-gamma-CD promoted off-pathway aggregation. Spectroscopic studies indicated that the hydrophobic exposure of the unstructured species in the refolded solutions was gradually reduced by the three HPCDs with the efficiency HP-beta-CD > HP-gamma-CD > HP-alpha-CD. Furthermore, the fast phase of aminoacylase reactivation was slowed down by the addition of 75 mM HP-beta- and gamma-CD, but no significant effect was observed for HP-alpha-CD. The dissimilarity in the effects of the three HPCDs suggested that the internal cavity size played a crucial role in their antiaggregation ability. Further analysis suggested that the observations might be much more complicated than expected because of the various types of interactions between cyclodextrins and proteins in addition to their ability to bind to protein aromatic residues.

Ionic liquids as refolding additives: N'-alkyl and N'-(omega-hydroxyalkyl) N-methylimidazolium chlorides

The purpose of this work was to investigate the influence of a series of N'-alkyl and N'-(omega-hydroxy-alkyl)-N-methylimidazolium chlorides on the renaturation of two model proteins, namely hen egg white lysozyme and the single-chain antibody fragment ScFvOx. All tested ionic liquids acted as refolding enhancers, with varying efficacies and efficiencies. The results of the refolding screening could be interpreted by taking into account the effect of the studied ionic liquids on protein aggregation, together with the systematic variations of their influence on the stability of native proteins in solution. More hydrophobic imidazolium cations carrying longer alkyl chains were increasingly destabilizing, while terminal hydroxylation of the alkyl chain made the salts more compatible with protein stability. The studied ionic liquids can be classified as preferentially bound, slightly to moderately chaotropic cosolvents for proteins.

L-Arginine increases the solubility of unfolded species of hen egg white lysozyme

L-Arginine (L-Arg) has been widely used as an enhancer of protein renaturation. The mechanism behind its action is still not fully understood. Using hen egg white lysozyme as a model protein, we present data that clearly demonstrate the suppression of the aggregation of denatured protein by L-Arg. By chemical modification of free cysteines, a series of unfolded lysozyme species were obtained that served as models for unfolded and intermediate states during the process of oxidative refolding. An increased equilibrium solubility of unfolded species and intermediates in the presence of L-Arg seems to be its major mechanism of action.

Understanding the relationship between the primary structure of proteins and its propensity to be soluble on overexpression in Escherichia coli

Solubility of proteins on overexpression in Escherichia coli is a manifestation of the net effect of several sequence-dependent and sequence-independent factors. This study aims to delineate the relationship between the primary structure and solubility on overexpression. The amino acid sequences of proteins reported to be soluble or to form inclusion bodies on overexpression in E. coli under normal growth conditions were analyzed. The results show a positive correlation between thermostability and solubility of proteins, and an inverse correlation between the in vivo half-life of proteins and solubility. The amino acid (Asn, Thr, Tyr) composition and the tripeptide frequency of the protein were also found to influence its solubility on overexpression. The amino acids that were seen to be present in a comparatively higher frequency in inclusion body-forming proteins have a higher sheet propensity, whereas those that are seen more in soluble proteins have a higher helix propensity; this is indicative of a possible correlation between sheet propensity and inclusion body formation. Thus, the present analysis shows that thermostability, in vivo half-life, Asn, Thr, and Tyr content, and tripeptide composition of a protein are correlated to the propensity of a protein to be soluble on overexpression in E. coli. The precise mechanism by which these properties affect the solubility status of the overexpressed protein remains to be understood.

Structural basis for cyclodextrins' suppression of human growth hormone aggregation

Many therapeutic proteins require storage at room temperature for extended periods of time. This can lead to aggregation and loss of function. Cyclodextrins (CDs) have been shown to function as aggregation suppressors for a wide range of proteins. Their potency is often ascribed to their affinity for aromatic amino acids, whose surface exposure would otherwise lead to protein association. However, no detailed structural studies are available. Here we investigate the interactions between human growth hormone (hGH) and different CDs at low pH. Although hGH aggregates readily at pH 2.5 in 1 M NaCl to form amorphous aggregates, the presence of 25 to 50 mM of various beta-CD derivatives is sufficient to completely avoid this. alpha- and gamma-CD are considerably less effective. Stopped-flow data on the aggregation reaction in the presence of beta-CD are analyzed according to a minimalist association model to yield an apparent hGH-beta-CD dissociation constant of approximately 6 mM. This value is very similar to that obtained by simple fluorescence-based titration of hGH with beta-CD. Nuclear magnetic resonance studies indicate that beta-CD leads to a more unfolded conformation of hGH at low pH and predominantly binds to the aromatic side-chains. This indicates that aromatic amino acids are important components of regions of residual structure that may form nuclei for aggregation.

Artificial chaperone mediated refolding of xylanase from an alkalophilic thermophilic Bacillus sp. Implications for in vitro protein renaturation via a folding intermediate

To gain insight into the molecular aspects of unfolding/refolding of enzymes from extremophilic organisms, we have used xylanase from an alkalophilic thermophilic Bacillus as the model system. Kinetics of denaturation/renaturation were monitored using intrinsic fluorescence studies. The protein fluorescence measurements suggested a putative intermediate state present in 0.08 M guanidine hydrochloride with an emission maximum of 345 nm; the far-UV circular dichroism spectra revealed content of secondary structure similar to the native enzyme. Studies with the fluorescent apolar probe 1-anilinonapthalene-8-sulfonate (1,8-ANS) were consistent with the presence of increased hydrophobic surfaces as compared with the native or fully unfolded protein. The refolding of Xyl II, was attempted by a relatively new strategy using an artificial chaperone assisted two-step method. The unfolded xylanase was found to bind to the detergent transiently and the subsequent addition of methyl-beta-cyclodextrin helped to strip the detergent and assist in the folding. Our findings suggested that the detergent stabilized a putative intermediate in the folding pathway seemingly equivalent to the folding state described as molten globule. The reactivation of Xyl II was affected by ionic as well as nonionic detergents. However, the cationic detergent cetyltrimethylammonium bromide (CTAB) provided a maximum reactivation (threefold) of the enzyme. The 'delayed detergent addition' experiments revealed that the detergent acts by suppressing the initial aggregate formation and not by dissolving aggregates. The relevance of our findings to the role of artificial chaperones in vivo is discussed.

Active-site sulfhydryl chemistry plays a major role in the misfolding of urea-denatured rhodanese

Unfolded bovine rhodanese, a sulfurtransferase, does not regain full activity upon refolding due to the formation of aggregates and disulfide-linked misfolded states unless a large excess of reductant such as 200 mM beta-ME and 5 mg/ml detergent are present [Tandon and Horowitz (1990), J. Biol. Chem. 265, 5967]. Even then, refolding is incomplete. We have studied the unfolding and refolding of three rhodanese forms whose crystal structures are known: ES, containing the transferred sulfur as a persulfide; E, without the transferred sulfur, and carboxymethylated rhodanese (CMR), in which the active site was blocked by chemical modification. The X-ray structures of ES, E, and CMR are virtually the same, but their tertiary structures in solution differ somewhat as revealed by near-UV CD. Among these three, CMR is the only form of rhodanese that folds reversibly, requiring 1 mM DTT. A minimum three-state folding model of CMR (N<-->I<-->U) followed by fluorescence at 363 nm, (N<-->I) by fluorescence at 318 nm, and CD (I<-->U) is consistent with the presence of a thermodynamically stable molten globule intermediate in 5-6 M urea. We conclude that the active-site sulfhydryl group in the persulfide form is very reactive; therefore, its modification leads to the successful refolding of urea-denatured rhodanese even in the absence of a large excess of reductant and detergent. The requirement for DTT for complete reversibility of CMR suggests that oxidation among the three non-active-site SH groups can represent a minor trap for refolding through species that can be easily reduced.

Artificial chaperoning of insulin, human carbonic anhydrase and hen egg lysozyme using linear dextrin chains--a sweet route to the native state of globular proteins

Linear dextrins (alpha-1,4-D-glucopyranoside chains) are known to possess amphiphilic surfaces and solubilize lipophilic compounds. We have assessed the ability of this amphiphilic surface of dextrin to inhibit the self-aggregation and assist the refolding of proteins. Addition of decameric dextrin, or dextrin-10, in the renaturation buffer improves the refolding yield of human carbonic anhydrase from its guanidinium chloride-induced denatured state. It is also seen to inhibit the self-aggregation of insulin. The ability of dextrin-10 to interact with cetyltrimethylammonium bromide and postpone its critical micellar concentration allows the use of dextrin-10 as a 'detergent stripping agent' in a novel artificial chaperoning process described earlier. The aggregation of human carbonic anhydrase and lysozyme upon refolding is prevented by cetyltrimethylammonium bromide due to the formation of a protein-detergent complex; dextrin-10 strips off the detergent from the complex and allow the proteins to fold, thus increasing the renaturation yield. Dextran-4 (the alpha-1,6-D-glucopyranoside chain), which does not exhibit amphiphilic properties, does not help in such artificial chaperoning.

Mechanistic comparison of artificial-chaperone-assisted and unassisted refolding of urea-denatured carbonic anhydrase B

BACKGROUND

We have previously described a method for the refolding of chemically denatured proteins in which small molecules ('artificial chaperones', a detergent and cyclodextrin) assist renaturation. In a previous analysis of lysozyme refolding from the GdmCl-denatured, DTT-reduced state, we found that enzymatic activity is regained at indistinguishable rates for unassisted (absence of additives) and artificial-chaperone-assisted refolding. While unassisted and artificial-chaperone-assisted refolding rates could also be directly compared for GdmCl-denatured bovine carbonic anhydrase B (CAB), only cationic detergents could be used as assistants. We therefore set out to determine whether artificial chaperones could assist the refolding of urea-denatured CAB, whether the charge and structure of the detergent used affects refolding assistance, and, if so, whether the assistance is mechanistically similar to that observed for GdmCl-denatured CAB.

RESULTS

Our results indicate that CAB can be refolded from the urea-denatured state via the artificial chaperone process, using both anionic and cationic detergents. There is a distinctive product-determining step early in the artificial-chaperone-assisted refolding mechanism, but the rate-determining steps of the unassisted and artificial-chaperone-assisted processes are indistinguishable.

CONCLUSIONS

Because the rate-determining steps of unassisted and artificial-chaperone-assisted refolding are indistinguishable, we conclude that the rate-determining step of CAB refolding is unaffected by the use of artificial chaperones. Our observations also suggest that denatured CAB undergoes a slow partial folding in concentrated urea solution.

Artificial chaperone-assisted refolding of citrate synthase

The power of genetic engineering methods, along with increasing genomic information, makes heterologous expression of proteins an extremely important biochemical tool. Unfortunately, proteins obtained in this way often are not in their native form, and folding becomes a crucial step in protein production. We have recently developed a strategy that promotes the folding of chemically denatured proteins via the sequential addition of low molecular weight "artificial chaperones." Here we describe in detail the application of this method to porcine heart citrate synthase. Refolding yields of as high as 65% have been achieved. Mechanistic studies indicate that there are significant differences between artificial chaperone-assisted refolding of citrate synthase and artificial chaperone-assisted refolding of two other proteins that have been examined, carbonic anhydrase B (Rozema, D., and Gellman, S. H. (1996) J. Biol. Chem. 271, 3478-3487) and lysozyme (Rozema, D., and Gellman, S. H. (1996) Biochemistry 35, 15760-15771). The differences among these three test proteins reveal the range of procedural variation that must be considered in the application of the artificial chaperone method to new proteins.

Permeation of unfolded basic fibroblast growth factor (bFGF) across rabbit buccal mucosa--does unfolding of bFGF enhance transport?

PURPOSE

To investigate whether recombinant human basic fibroblast growth factor (rhbFGF) would permeate freshly-excised rabbit buccal mucosa. In addition, the effect of a permeation enhancer (Na+ glycocholate) and the possibility of reversibly unfolding the globular protein to a more linear conformation to increase the permeability of the test protein was evaluated.

METHODS

The in vitro flux of bFGF through freshly-excised rabbit buccal mucosa was determined using side-by-side diffusion systems. Detection of bFGF was performed using gradient elution, reversed-phase high-pressure liquid chromatography (RP-HPLC). Fluorescence spectroscopy and heparin affinity chromatography were used to assess the tertiary structure of bFGF.

RESULTS

Preliminary in vitro results have demonstrated that the bFGF flux increased from 1.4 +/- 0.13 ng min-1 cm-2 to 3.2 +/- 0.38 ng min-1 cm-2 with the addition of 15 mM Na+ glycocholate (NaG) to the donor solution. Subsequent addition of guanidine HCl (GnHCl) to the donor solution (3 M) was not followed by a further increase in the flux of bFGF (2.9 +/- 0.26 ng min-1 cm-2). However, when the order of addition of the additives was reversed (GnHCl first followed by NaG), the flux of bFGF across rabbit buccal mucosa was increased. Upon addition of GnHCl, there was a significant (p < .05) increase in bFGF flux from 1.2 +/- 0.15 ng min-1 cm-2 to 5.0 +/- 0.58 ng min-1 cm-2. Addition of NaG further increased the flux to 8.5 +/- 1.1 ng min-1 cm-2 which was approximately 3- to 3.5-fold greater than that determined with the protein alone in the absence of any donor phase additives. The percent of parent bFGF remaining following a 3-hr exposure of a bFGF solution to either the mucosal, serosal, or both sides of rabbit buccal mucosa were 54.3 +/- 5.7%, 71.8 +/- 6.3%, and 36.2 +/- 5.4%, respectively with the majority of parent bFGF lost during the first 15 minutes. A model endopeptidase (endoproteinase Arg-C from mouse submaxillary gland) was shown in vitro to contribute to the loss in parent bFGF.

CONCLUSIONS

The permeation of bFGF across rabbit buccal mucosa may be significantly increased by initially unfolding the protein with GnHCl and then treating the tissue with the permeation enhancer, NaG. Refolding and possible reactivation of bFGF's bioactivity may occur following membrane transport and subsequent dilution into an infinite sink.

Renaturation of rhodanese by translational elongation factor (EF) Tu. Protein refolding by EF-Tu flexing

The translation elongation factor (EF) Tu has chaperone-like capacity to promote renaturation of denatured rhodanese. This renaturation activity is greatly increased under conditions in which the factor can oscillate between the open and closed conformations that are induced by GDP and GTP, respectively. Oscillation occurs during GTP hydrolysis and subsequent replacement of GDP by EF-Ts which is then displaced by GTP. Renaturation of rhodanese and GTP hydrolysis by EF-Tu are greatly enhanced by the guanine nucleotide exchange factor EF-Ts. However, renaturation is reduced under conditions that stabilize EF-Tu in either the open or closed conformation. Both GDP and the nonhydrolyzable analog of GTP, GMP-PCP, inhibit renaturation. Kirromycin and pulvomycin, antibiotics that specifically bind to EF-Tu and inhibit its activity in peptide elongation, also strongly inhibit EF-Tu-mediated renaturation of denatured rhodanese to levels near those observed for spontaneous, unassisted refolding. Kirromycin locks EF-Tu in the open conformation in the presence of either GTP or GDP, whereas pulvomycin locks the factor in the closed conformation. The results lead to the conclusion that flexing of EF-Tu, especially as occurs between its open and closed conformations, is a major factor in its chaperone-like refolding activity.

Ribosomes and ribosomal RNA as chaperones for folding of proteins

BACKGROUND

Provocative recent reports indicate that the large subunits of either prokaryotic or eukaryotic ribosomes have the capacity to promote refolding of denatured enzymes.

RESULTS

Salt-washed Escherichia coli ribosomes are shown to promote refolding of denatured rhodanese. The ability of the ribosomes to carry out renaturation is a property of the 50S ribosomal subunit, specifically the 23S rRNA. Refolding and release of enzymatically active rhodanese leaves the ribosomes in an inactive state or conformation for subsequent rounds refolding. Inactive ribosomes can be activated by elongation factor G (EF-G) plus GTP or by cleavage of their 23S rRNA by alpha-sarcin. Activation by either mechanism is strongly inhibited by the EF-G.GDP.fusidic acid complex.

CONCLUSIONS

Large subunits of E. coli ribosomes, specifically 23S rRNA, have the capacity to mediate refolding of denatured rhodanese. Refolding activity is related to the state or conformation of ribosomes that is promoted by EF-G. Activation by either mechanism is strongly inhibited by the EF-G.GDP.fusidic acid complex.

Artificial chaperone-assisted refolding of denatured-reduced lysozyme: modulation of the competition between renaturation and aggregation

Conditions that promote renaturation of an unfolded protein also promote protein aggregation, in many cases, because these competing intramolecular and intermolecular processes are driven by similar networks of noncovalent interactions. The GroEL/GroES system and related biological chaperones facilitate the renaturation of substrate proteins by minimizing the aggregation pathway. We have devised a two-step method in which small molecules, "artificial chaperones," facilitate protein refolding from a chemically denatured state. In the first step, the protein is captured by a detergent as guanidinium chloride is diluted to a non-denaturing concentration; formation of a protein-detergent complex prevents both protein aggregation and proper refolding. In the second step, a cyclodextrin strips detergent from the protein, allowing the protein to refold. Here we describe the first application of this method to a protein that must form disulfides in the native state. Lysozyme (hen egg white) can be refolded from the Gdm-denatured, DTT-reduced state in good yields at final protein concentrations as high as 1 mg/mL with the artificial chaperone method. Several mechanistic aspects of artificial chaperone-assisted refolding have been probed, and a detailed mechanism for the kinetically controlled stripping step is proposed.

Renaturation of glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides after denaturation in 4 M guanidine hydrochloride: kinetics of aggregation and reactivation

In 4 M guanidine hydrochloride (GdnHCl), the dimeric enzyme glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides (G6PD) dissociated to subunits and was extensively unfolded. Rapid dilution of this high GdnHCl concentration allowed G6PD to partially renature, as measured by enzyme reactivation, to a level which depended on the conditions employed. The fraction of the enzyme which did not renature aggregated and precipitated out of solution, a process which could not be substantially prevented by stabilizing additives. Based on the enzyme concentration dependence of the reactivation yield and on a comparison of the aggregation and reactivation rates, it was determined that aggregation and reactivation compete kinetically for a partially-folded intermediate only very early in the process, during the rapid GdnHCl-dilution step. The kinetics of G6PD reactivation were sigmoidal, indicating that this process involves more than one rate-limiting reaction. The kinetics depended on enzyme concentration in a higher than first-order manner, indicating that association of subunits is one of the rate-limiting reactions. A renaturation mechanism compatible with these observations is described, which involves a bi-unimolecular (subunit association-folding) reaction sequence, with rate constants equal to 2.19 microM-1 min-1 and 0.140 min-1, respectively. This mechanism involves an inactive, dimeric, G6PD-folding intermediate, a species whose existence has recently been established by equilibrium denaturation experiments (Plomer, J.J. and Gafni, A. (1992) Biochim. Biophys. Acta 1122, 234-242).