Prevention of thermal aggregation of an allosteric protein by small molecules: Some mechanistic insights

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.

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.

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.

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.

Chaperonin-Based Biolayer Interferometry To Assess the Kinetic Stability of Metastable, Aggregation-Prone Proteins

Stabilizing the folded state of metastable and/or aggregation-prone proteins through exogenous ligand binding is an appealing strategy for decreasing disease pathologies caused by protein folding defects or deleterious kinetic transitions. Current methods of examining binding of a ligand to these marginally stable native states are limited because protein aggregation typically interferes with analysis. Here, we describe a rapid method for assessing the kinetic stability of folded proteins and monitoring the effects of ligand stabilization for both intrinsically stable proteins (monomers, oligomers, and multidomain proteins) and metastable proteins (e.g., low Tm) that uses a new GroEL chaperonin-based biolayer interferometry (BLI) denaturant pulse platform. A kinetically controlled denaturation isotherm is generated by exposing a target protein, immobilized on a BLI biosensor, to increasing denaturant concentrations (urea or GuHCl) in a pulsatile manner to induce partial or complete unfolding of the attached protein population. Following the rapid removal of the denaturant, the extent of hydrophobic unfolded/partially folded species that remains is detected by an increased level of GroEL binding. Because this kinetic denaturant pulse is brief, the amplitude of binding of GroEL to the immobilized protein depends on the duration of the exposure to the denaturant, the concentration of the denaturant, wash times, and the underlying protein unfolding-refolding kinetics; fixing all other parameters and plotting the GroEL binding amplitude versus denaturant pulse concentration result in a kinetically controlled denaturation isotherm. When folding osmolytes or stabilizing ligands are added to the immobilized target proteins before and during the denaturant pulse, the diminished population of unfolded/partially folded protein manifests as a decreased level of GroEL binding and/or a marked shift in these kinetically controlled denaturation profiles to higher denaturant concentrations. This particular platform approach can be used to identify small molecules and/or solution conditions that can stabilize or destabilize thermally stable proteins, multidomain proteins, oligomeric proteins, and, most importantly, aggregation-prone metastable proteins.

Advanced protein formulations

It is well recognized that protein product development is far more challenging than that for small-molecule drugs. The major challenges include inherent sensitivity to different types of stresses during the drug product manufacturing process, high rate of physical and chemical degradation during long-term storage, and enhanced aggregation and/or viscosity at high protein concentrations. In the past decade, many novel formulation concepts and technologies have been or are being developed to address these product development challenges for proteins. These concepts and technologies include use of uncommon/combination of formulation stabilizers, conjugation or fusion with potential stabilizers, site-specific mutagenesis, and preparation of nontraditional types of dosage forms-semiaqueous solutions, nonfreeze-dried solid formulations, suspensions, and other emerging concepts. No one technology appears to be mature, ideal, and/or adequate to address all the challenges. These gaps will likely remain in the foreseeable future and need significant efforts for ultimate resolution.

Thermal disaggregation of type B yeast hexokinase by indole derivatives: a mechanistic study

Protein aggregation is a pathological hallmark of several human disorders, and a central problem in biotechnology, occurring during purification, sterilization, shipping and storage of protein structures. The process is a very complex one, characterized with a remarkable polymorphism of aggregates, including soluble amyloid oligomers, amyloid fibrils and amorphous species. While amyloid structure formation has been extensively investigated during the recent years, amorphous aggregation is still not well characterized. Use of small molecules that affect this process could be informative in this regard. In order to explore the inhibiting effect of small molecules on the amorphous aggregate formation, yeast hexokinase-B, a key enzyme in metabolism, has been chosen for the present study. Thermal aggregation of the enzyme was investigated in 50 mM phosphate buffer, pH 7 at 55°C and the extent of aggregation was measured by monitoring the increase in absorbance at 350 nm versus time. Possible anti-aggregation effects of a variety of non-specific ligands including indole, tryptophan, carbinol, and indomethacin were explored. Turbidity of the protein solutions was found to be diminished by the presence of these small molecules in the above conditions, with the highest effects being exerted by indomethacin. Dynamic light scattering and HPLC confirmed that indomethacin had the highest anti-aggregation effect. These observations, taken together, suggest that the indole ring is likely to play an important role in aggregation inhibition.