Effect of Arginine on Chaperone-Like Activity of HspB6 and Monomeric 14-3-3ζ

Polyamines putrescine and spermidine as modulators of protein aggregation rate: The effect on DTT-induced aggregation of α-lactalbumin

Protein aggregation is undesirable for cells due to its possible toxicity, and is also undesirable in biotechnology and pharmaceuticals. Polyamines are known to be capable of both suppressing and stimulating protein aggregation. In the present work polyamines (spermidine, putrescine) have been shown to alter the pathway of α-lactalbumin aggregation induced by dithiothreitol, leading to the formation of larger protein particles during the initial stages of aggregation and promoting the later stage of sticking of aggregates. According to the aggregation kinetics data, polyamines accelerate protein aggregation in a concentration-dependent manner, with a maximum at 50 mM spermidine and 100 mM putrescine. With a further increase in polyamines concentration the effect of aggregation acceleration decreased, thus, the modulation of the aggregation rate by polyamines was shown. A comparison of the aggregation kinetics and hydrodynamic radii growth data registered by dynamic light scattering with the data obtained by asymmetric flow field-flow fractionation and analytical ultracentrifugation allowed us to describe the early stages of aggregation and formation of initial α-lactalbumin clusters. Our results provide a deeper insight into the mechanism of amorphous aggregation of α-lactalbumin and polyamines action on protein aggregation and protein-protein interaction in general.

Effects of osmolytes under crowding conditions on the properties of muscle glycogen phosphorylase b

The study of the relationship between the activity and stability of enzymes under crowding conditions in the presence of osmolytes is important for understanding the functioning of a living cell. The effect of osmolytes (trehalose and betaine) on the secondary and tertiary structure and activity of muscle glycogen phosphorylase b (Phb) under crowding conditions created by PEG 2000 and PEG 20000 was investigated using dynamic light scattering, differential scanning calorimetry, circular dichroism spectroscopy, fluorimetry and enzymatic activity assay. At 25 °C PEGs increased Phb activity, but PEG 20000 to a greater extent. Wherein, PEG 20000 significantly destabilized its tertiary and secondary structure, in contrast to PEG 2000. Trehalose removed the effects of PEGs on Phb, while betaine significantly reduced the activating effect of PEG 20000 without affecting the action of PEG 2000. Under heat stress at 48 °C, the protective effect of osmolytes under crowding conditions was more pronounced than at room temperature, and the Phb activity in the presence of osmolytes was higher in these conditions than in diluted solutions. These results provide important insights into the complex mechanism, by which osmolytes affect the structure and activity of Phb under crowding conditions.

Metabolic deregulation associated with aging modulates protein aggregation in the yeast model of Huntington's disease

Huntington's disease is associated with increased CAG repeat resulting in an expanded polyglutamine tract in the protein Huntingtin (HTT) leading to its aggregation resulting in neurodegeneration. Previous studies have shown that N-terminal HTT with 46Q aggregated in the stationary phase but not the logarithmic phase in the yeast model of HD. We carried out a metabolomic analysis of logarithmic and stationary phase yeast model of HD expressing different polyQ lengths attached to N-terminal HTT tagged with enhanced green fluorescent protein (EGFP). The results show significant changes in the metabolic profile and deregulated pathways in stationary phase cells compared to logarithmic phase cells. Comparison of metabolic pathways obtained from logarithmic phase 46Q versus 25Q with those obtained for presymptomatic HD patients from our previous study and drosophila model of HD showed considerable overlap. The arginine biosynthesis pathway emerged as one of the key pathways that is common in stationary phase yeast compared to logarithmic phase and HD patients. Treatment of yeast with arginine led to a significant decrease, while transfer to arginine drop-out media led to a significant increase in the size of protein aggregates in both logarithmic and stationary phase yeast model of HD. Knockout of arginine transporters in the endoplasmic reticulum and vacuole led to a significant decrease in mutant HTT aggregation. Overall our results highlight arginine as a critical metabolite that modulates the aggregation of mutant HTT and disease progression in HD.Communicated by Ramaswamy H. Sarma.

Refolding Increases the Chaperone-like Activity of αH-Crystallin and Reduces Its Hydrodynamic Diameter to That of α-Crystallin

αH-Crystallin, a high molecular weight form of α-crystallin, is one of the major proteins in the lens nucleus. This high molecular weight aggregate (HMWA) plays an important role in the pathogenesis of cataracts. We have shown that the chaperone-like activity of HMWA is 40% of that of α-crystallin from the lens cortex. Refolding with urea significantly increased-up to 260%-the chaperone-like activity of α-crystallin and slightly reduced its hydrodynamic diameter (Dh). HMWA refolding resulted in an increase in chaperone-like activity up to 120% and a significant reduction of Dh of protein particles compared with that of α-crystallin. It was shown that the chaperone-like activity of HMWA, α-crystallin, and refolded α-crystallin but not refolded HMWA was strongly correlated with the denaturation enthalpy measured with differential scanning calorimetry (DSC). The DSC data demonstrated a significant increase in the native protein portion of refolded α-crystallin in comparison with authentic α-crystallin; however, the denaturation enthalpy of refolded HMWA was significantly decreased in comparison with authentic HMWA. The authors suggested that the increase in the chaperone-like activity of both α-crystallin and HMWA could be the result of the correction of misfolded proteins during renaturation and the rearrangement of protein supramolecular structures.

Effect of Chemical Chaperones on the Stability of Proteins during Heat- or Freeze-Thaw Stress

The importance of studying the structural stability of proteins is determined by the structure-function relationship. Protein stability is influenced by many factors among which are freeze-thaw and thermal stresses. The effect of trehalose, betaine, sorbitol and 2-hydroxypropyl-β-cyclodextrin (HPCD) on the stability and aggregation of bovine liver glutamate dehydrogenase (GDH) upon heating at 50 °C or freeze-thawing was studied by dynamic light scattering, differential scanning calorimetry, analytical ultracentrifugation and circular dichroism spectroscopy. A freeze-thaw cycle resulted in the complete loss of the secondary and tertiary structure, and aggregation of GDH. All the cosolutes suppressed freeze-thaw- and heat-induced aggregation of GDH and increased the protein thermal stability. The effective concentrations of the cosolutes during freeze-thawing were lower than during heating. Sorbitol exhibited the highest anti-aggregation activity under freeze-thaw stress, whereas the most effective agents stabilizing the tertiary structure of GDH were HPCD and betaine. HPCD and trehalose were the most effective agents suppressing GDH thermal aggregation. All the chemical chaperones stabilized various soluble oligomeric forms of GDH against both types of stress. The data on GDH were compared with the effects of the same cosolutes on glycogen phosphorylase b during thermal and freeze-thaw-induced aggregation. This research can find further application in biotechnology and pharmaceutics.

Investigating the role of double mutations R12C/P20R, and R12C/R69C on structure, chaperone-like activity, and amyloidogenic properties of human αB-crystallin

α-crystallin is a structurally essential small heat shock protein (sHSP) with a chaperone-like activity which maintains transparency of the lenticular tissues during a period of time that is as long as human life. α-crystallin is a multimeric protein consisting of αA and αB subunits, with 57 % homology. The CRYAB gene on chromosome 11 encodes human αB-crystallin (αB-Cry), which contains 175 amino acid residues. In the current study, the cataractogenic mutations R12C, P20R, R69C, and double mutations R12C/P20R and R12C/P20R were embedded into the human CRYAB gene. Following successful expression in the prokaryotic system and purification, a number of spectroscopic techniques, gel electrophoresis, dynamic light scattering (DLS), and transmission electron microscopy (TEM) were applied to assess the role of these mutations on the structure, amyloidogenicity, and biological function of human αB-Cry. The created mutations caused significant changes in the structure, and oligomeric state of human αB-Cry. These mutations, particularly R12C, R12C/P20R, and R12C/R69C, dramatically enhanced the tendency of this protein for the amyloid fibril formation and reduced its chaperone-like activity. Since double mutations R12C/P20R and R12C/P20R were able to intensely change the protein's structure and chaperone function, it can be suggested that they may play a destructive role in a cumulative manner. Our findings indicated that the simultaneous presence of two pathogenic mutations may have a cumulative destructive impacts on the structure and function of human αB-Cry and this observation is likely related to the disease severity of the mutated proteins.

Oxidative damage to βL-crystallin in vitro by iron compounds formed in physiological buffers

β_L-crystallin aggregation due to oxidative damage in the presence of H₂O₂ and ferric chloride was studied in-vitro under conditions close to physiological. It was shown that the protein aggregation characterized by the nucleation time and the aggregation rate significantly depended on the composition of the isoosmotic buffers used, and decreased in the series HEPES buffer > Tris buffer > PBS. Ferric chloride at neutral pH was converted into water-insoluble iron hydroxide III (≡Fe^IIIOH). According to the data of scanning electron microscopy the ≡Fe^IIIOH particles formed in HEPES buffer, Tris buffer, and PBS practically did not differ in structure. However, the sizes of ≡Fe^IIIOH floating particles measured by dynamic light scattering differed significantly and were 44 ± 28 nm, 93 ± 66 nm, 433 ± 316 nm (Z_aver ± SD) for HEPES buffer, Tris buffer, and PBS, respectively. It was found by the spin trap method that the ability of ≡Fe^IIIOH to decompose H₂O₂ with the formation of a ^•OH decreases in the series HEPES buffer, Tris buffer, and PBS. The authors suggest that the ability to generate ^•OH during the decomposition of H₂O₂ is determined by the total surface area of ≡Fe^IIIOH particles, which significantly depends on the composition of the buffer in which these particles are formed.

The Effect of Chemical Chaperones on Proteins with Different Aggregation Kinetics

Formation and accumulation of protein aggregates adversely affect intracellular processes in living cells and are negative factors in the production and storage of protein preparations. Chemical chaperones can prevent protein aggregation, but this effect is not universal and depends on the target protein structure and kinetics of its aggregation. We studied the effect of betaine (Bet) and lysine (Lys) on thermal aggregation of muscle glycogen phosphorylase b (Phb) at 48°C (aggregation order, n = 0.5), UV-irradiated Phb (UV-Phb) at 37°C (n = 1), and apo-form of Phb (apo-Phb) at 37°C (n = 2). Using dynamic light scattering, differential scanning calorimetry, and analytical ultracentrifugation, we have shown that Bet protected Phb and apo-Phb from aggregation, but accelerated the aggregation of UV-Phb. At the same time, Lys prevented UV-Phb and apo-Phb aggregation, but increased the rate of Phb aggregation. The mechanisms of chemical chaperone action on the tertiary and quaternary structures and kinetics of thermal aggregation of the target proteins are discussed. Comparison of the effects of chemical chaperones on the proteins with different aggregation kinetics provides more complete information on the mechanism of their action.

Effects of Molecular Crowding and Betaine on HSPB5 Interactions, with Target Proteins Differing in the Quaternary Structure and Aggregation Mechanism

The aggregation of intracellular proteins may be enhanced under stress. The expression of heat-shock proteins (HSPs) and the accumulation of osmolytes are among the cellular protective mechanisms in these conditions. In addition, one should remember that the cell environment is highly crowded. The antiaggregation activity of HSPB5 and the effect on it of either a crowding agent (polyethylene glycol (PEG)) or an osmolyte (betaine), or their mixture, were tested on the aggregation of two target proteins that differ in the order of aggregation with respect to the protein: thermal aggregation of glutamate dehydrogenase and DTT-induced aggregation of lysozyme. The kinetic analysis of the dynamic light-scattering data indicates that crowding can decrease the chaperone-like activity of HSPB5. Nonetheless, the analytical ultracentrifugation shows the protective effect of HSPB5, which retains protein aggregates in a soluble state. Overall, various additives may either improve or impair the antiaggregation activity of HSPB5 against different protein targets. The mixed crowding arising from the presence of PEG and 1 M betaine demonstrates an extraordinary effect on the oligomeric state of protein aggregates. The shift in the equilibrium of HSPB5 dynamic ensembles allows for the regulation of its antiaggregation activity. Crowding can modulate HSPB5 activity by affecting protein-protein interactions.

Effect of Betaine and Arginine on Interaction of αB-Crystallin with Glycogen Phosphorylase b

Protein-protein interactions (PPIs) play an important role in many biological processes in a living cell. Among them chaperone-client interactions are the most important. In this work PPIs of αB-crystallin and glycogen phosphorylase b (Phb) in the presence of betaine (Bet) and arginine (Arg) at 48 °C and ionic strength of 0.15 M were studied using methods of dynamic light scattering, differential scanning calorimetry, and analytical ultracentrifugation. It was shown that Bet enhanced, while Arg reduced both the stability of αB-crystallin and its adsorption capacity (AC₀) to the target protein at the stage of aggregate growth. Thus, the anti-aggregation activity of αB-crystallin increased in the presence of Bet and decreased under the influence of Arg, which resulted in inhibition or acceleration of Phb aggregation, respectively. Our data show that chemical chaperones can influence the tertiary and quaternary structure of both the target protein and the protein chaperone. The presence of the substrate protein also affects the quaternary structure of αB-crystallin, causing its disassembly. This is inextricably linked to the anti-aggregation activity of αB-crystallin, which in turn affects its PPI with the target protein. Thus, our studies contribute to understanding the mechanism of interaction between chaperones and proteins.

Effect of Trehalose on Oligomeric State and Anti-Aggregation Activity of αB-Crystallin

αB-Crystallin (αB-Cr), one of the main crystalline lens proteins, along with other crystallins maintains lens transparency suppressing protein aggregation and thus preventing cataractogenesis. αB-Cr belongs to the class of molecular chaperones; being expressed in many tissues it has a dynamic quaternary structure, which is essential for its chaperone-like activity. Shift in the equilibrium between ensembles of oligomers of different size allows regulating the chaperone activity. Trehalose is known to inhibit protein aggregation in vivo and in vitro, and it is widely used in biotechnology. The results of studying the effect of trehalose on the chaperone-like activity of crystallins can serve as a basis for the design of drugs delaying cataractogenesis. We have studied the trehalose effect on the quaternary structure and anti-aggregation activity of αB-Cr using muscle glycogen phosphorylase b (Phb) as a target protein. According to the dynamic light scattering data, trehalose affects the nucleation stage of Phb thermal aggregation at 48°C, and an increase in the αB-Cr adsorption capacity (AC₀) is the main effect of trehalose on the aggregation process in the presence of the protein chaperone (AC₀ increases 1.5-fold in the presence of 66 mM trehalose). According to the sedimentation analysis data, trehalose stabilizes the dimeric form of Phb at the stages of denaturation and dissociation and enhances the interaction of αB-Cr with the target protein. Moreover, trehalose shifts the equilibrium between the αB-Cr oligomers towards the smaller forms. Thus, trehalose affects the quaternary structure of αB-Cr and increases its anti-aggregation activity at the nucleation stage.

Combined action of chemical chaperones on stability, aggregation and oligomeric state of muscle glycogen phosphorylase b

Chemical chaperones are a class of small molecules, which enhance protein stability, folding, inhibit protein aggregation, and are used for long-term storage of therapeutic proteins. The combined action of chemical chaperones trehalose, betaine and lysine on stability, aggregation and oligomeric state of muscle glycogen phosphorylase b (Phb) has been studied. Dynamic light scattering data indicate that the affinity of trehalose to Phb increased in the presence of betaine or lysine at both stages (stage of nucleation and aggregate growth) of enzyme aggregation at 48 °C, in contrast, the affinity of betaine to the enzyme in the presence of lysine remained practically unchanged. According to differential scanning calorimetry and analytical ultracentrifugation data, the mixture of trehalose and betaine stabilized Phb stronger than either of them in total. Moreover, the destabilizing effect of lysine on the enzyme was almost completely compensated by trehalose and only partially by betaine. The main protective effect of the mixtures of osmolytes and lysine is associated with their influence on the dissociation/denaturation stage, which is the rate-limiting one of Phb aggregation. Thus, a pair of chaperones affects the stability, oligomeric state, and aggregation of Phb differently than individual chaperones.

The mechanism of thermal aggregation of glutamate dehydrogenase. The effect of chemical chaperones

Chemical chaperones are low-molecular compounds counteracting protein aggregation. Understanding of the mechanism of their effects is key to their potential use in biotechnology. The aggregation of bovine liver glutamate dehydrogenase (GDH) was studied at 40 °C and 50 °C using dynamic light scattering, analytical ultracentrifugation, size-exclusion chromatography and differential scanning calorimetry. At 40 °C the GDH aggregation proceeds through the slow stages of hexamer dissociation and formation of small oligomeric aggregates. At 50 °C these stages are transient. The rate-limiting stage of the overall aggregation process is unfolding of the protein molecule; the order of aggregation with respect to protein, n = 1. The test system based on GDH aggregation at 50 °C was used to quantify the anti-aggregation activity of chemical chaperones by comparing their half-saturation concentrations [L]_0.5. Arginine ethyl ester had the highest anti-aggregation activity, with [L]_0.5 = 4 ± 1 mM. For other additives, [L]_0.5 was 22 ± 1 mM (arginine), 18 ± 1 mM (argininamide) and 95 ± 12 mM (proline). Arginine at concentrations up to 300 mM, argininamide at concentrations higher than 300 mM and arginine ethyl ester at concentrations higher than 500 mM enhance aggregate-aggregate sticking. These results explain the mechanism of heat-induced GDH aggregation and its peculiarities at different temperatures or in the presence of chemical chaperones.

Effect of arginine on stability and aggregation of muscle glycogen phosphorylase b

Arginine (Arg) is frequently used in biotechnology and pharmaceutics to stabilize protein preparations. When using charged ions like Arg, it is necessary to take into account their contribution to the increase in ionic strength, in addition to the effect of Arg on particular processes occurring under the conditions of constancy of ionic strength. Here, we examined contribution of ionic strength (0.15 and 0.5 M) to the effects of Arg on denaturation, thermal inactivation and aggregation of skeletal muscle glycogen phosphorylase b (Phb). Dynamic light scattering, analytical ultracentrifugation, differential scanning calorimetry, circular dichroism and enzymatic activity assay were used to assess the effects of Arg at constant ionic strength compared with the effects of ionic strength alone. We found that high ionic strength did not affect the secondary structure of Phb, but changed conformation of the protein. Such a destabilization of the enzyme causes an increase in the initial rate of aggregation and inactivation of Phb thereby affecting its denaturation. Binding of Arg causes additional changes in the protein conformation, weakening the bonds between monomers in the dimer. This causes the dimer to dissociate into monomers, which rapidly aggregate. Thus, Arg acts on these processes much stronger than just ionic strength.