Thermodynamic analysis of the stabilisation of pig heart mitochondrial malate dehydrogenase and maize leaf phosphoenolpyruvate carboxylase by different salts, amino acids and polyols

Kinetic Modeling, Thermodynamic Approach and Molecular Dynamics Simulation of Thermal Inactivation of Lipases from Burkholderia cepacia and Rhizomucor miehei

The behavior against temperature and thermal stability of enzymes is a topic of importance for industrial biocatalysis. This study focuses on the kinetics and thermodynamics of the thermal inactivation of Lipase PS from B. cepacia and Palatase from R. miehei. Thermal inactivation was investigated using eight inactivation models at a temperature range of 40–70 °C. Kinetic modeling showed that the first-order model and Weibull distribution were the best equations to describe the residual activity of Lipase PS and Palatase, respectively. The results obtained from the kinetic parameters, decimal reduction time (D and t_R), and temperature required (z and z’) indicated a higher thermal stability of Lipase PS compared to Palatase. The activation energy values (Ea) also indicated that higher energy was required to denature bacterial (34.8 kJ mol⁻¹) than fungal (23.3 kJ mol⁻¹) lipase. The thermodynamic inactivation parameters, Gibbs free energy (ΔG^#), entropy (ΔS^#), and enthalpy (ΔH^#) were also determined. The results showed a ΔG^# for Palatase (86.0–92.1 kJ mol⁻¹) lower than for Lipase PS (98.6–104.9 kJ mol⁻¹), and a negative entropic and positive enthalpic contribution for both lipases. A comparative molecular dynamics simulation and structural analysis at 40 °C and 70 °C were also performed.

Arginine and proline applied as food additives stimulate high freeze tolerance in larvae of Drosophila melanogaster

The fruit fly Drosophila melanogaster is an insect of tropical origin. Its larval stage is evolutionarily adapted for rapid growth and development under warm conditions and shows high sensitivity to cold. In this study, we further developed an optimal acclimation and freezing protocol that significantly improves larval freeze tolerance (an ability to survive at −5°C when most of the freezable fraction of water is converted to ice). Using the optimal protocol, freeze survival to adult stage increased from 0.7% to 12.6% in the larvae fed standard diet (agar, sugar, yeast, cornmeal). Next, we fed the larvae diets augmented with 31 different amino compounds, administered in different concentrations, and observed their effects on larval metabolomic composition, viability, rate of development and freeze tolerance. While some diet additives were toxic, others showed positive effects on freeze tolerance. Statistical correlation revealed tight association between high freeze tolerance and high levels of amino compounds involved in arginine and proline metabolism. Proline- and arginine-augmented diets showed the highest potential, improving freeze survival to 42.1% and 50.6%, respectively. Two plausible mechanisms by which high concentrations of proline and arginine might stimulate high freeze tolerance are discussed: (i) proline, probably in combination with trehalose, could reduce partial unfolding of proteins and prevent membrane fusions in the larvae exposed to thermal stress (prior to freezing) or during freeze dehydration; (ii) both arginine and proline are exceptional among amino compounds in their ability to form supramolecular aggregates which probably bind partially unfolded proteins and inhibit their aggregation under increasing freeze dehydration.

Daunomycin interaction with DNA: microcalorimetric studies of the thermodynamics and binding mechanism

Nucleic acids are an important target for many therapeutics. Small molecules that bind to nucleic acids are important in many aspects of medicines, particularly in cancer chemotherapy. In recent years, many studies have utilized polynucleic acids with various sequences to demonstrate the binding mechanism of daunomycin, a potent anticancer drug. This study describes that isothermal titration calorimetry is a useful tool for studying the fundamental binding mechanism systemically. The results suggest that the binding free energy is more favorable when the temperature is increased. The binding entropy contributes to this effect. Furthermore, the amine group on daunomycin contributes electrostatic interaction that induces the binding process. In addition, enthalpy-entropy compensation is also exhibited in the daunomycin-DNA binding mechanism. This study used an easy, convenient method of performing a systemic study in a recognition system. The results from this study provide additional information about microscopic mechanisms for molecular design and molecular recognition.

Osmophobic effect of glycerol on irreversible thermal denaturation of rabbit creatine kinase

Protein stability plays an extremely important role not only in its biological function but also in medical science and protein engineering. Osmolytes provide a general method to protect proteins from the unfolding and aggregation induced by extreme environmental stress. In this study, the effect of glycerol on protection of the model enzyme creatine kinase (CK) against heat stress was investigated by a combination of spectroscopic method and thermodynamic analysis. Glycerol could prevent CK from thermal inactivation and aggregation in a concentration-dependent manner. The spectroscopic measurements suggested that the protective effect of glycerol was a result of enhancing the structural stability of native CK. A further thermodynamic analysis using the activated-complex theory suggested that the effect of glycerol on preventing CK against aggregation was consistent with those previously established mechanisms in reversible systems. The osmophobic effect of glycerol, which preferentially raised the free energy of the activated complex, shifted the equilibrium between the native state and the activated complex in favor of the native state. A comparison of the inactivation rate and the denaturation rate suggested that the protection of enzyme activity by glycerol should be attributed to the enhancement of the structural stability of the whole protein rather than the flexible active site.

Structural and catalytic response to temperature and cosolvents of carboxylesterase EST1 from the extremely thermoacidophilic archaeon Sulfolobus solfataricus P1

The interactive effects of temperature and cosolvents on the kinetic and structural features of a carboxylesterase from the extremely thermoacidophilic archaeon Sulfolobus solfataricus P1 (Sso EST1) were examined. While dimethylformamide, acetonitrile, and dioxane were all found to be deleterious to enzyme function, dimethyl sulfoxide (DMSO) activated Sso EST1 to various extents. This was particularly true at 3.5% (v/v) DMSO, where k(cat) was 20-30% higher than at 1.2% DMSO, over the temperature range of 50-85 degrees C. DMSO compensated for thermal activation in some cases; for example, k(cat) at 60 degrees C in 3.5% DMSO was comparable to k(cat) at 85 degrees C in 1.2% DMSO. The relationship between DMSO activation and enzyme structural characteristics was also investigated. Nuclear magnetic resonance spectroscopy and circular dichroism showed no gross change in enzyme conformation with 3.5% DMSO between 50 and 80 degrees C. However, low levels of DMSO were shown to have a small yet significant change in enzyme conformation. This was evident through the reduction of Sso EST1's melting temperature and changes in the microenvironment of the enzyme's tyrosine and tryptophan residues at 3.5% versus 1.2% (v/v) solvent. Finally, activation parameter analysis based on kinetic data, at 1.2% and 3.5% DMSO, implied an increase in conformational flexibility with additional cosolvent. These results suggest the activating effect of DMSO was related to small changes in the enzyme's structure resulting in an increase in its conformational flexibility. Thus, in addition to their use for solubilizing hydrophobic substrates in water, cosolvents may also serve as activators in applications involving thermostable biocatalysts at sub-optimal temperatures.

Instability, stabilization, and formulation of liquid protein pharmaceuticals

One of the most challenging tasks in the development of protein pharmaceuticals is to deal with physical and chemical instabilities of proteins. Protein instability is one of the major reasons why protein pharmaceuticals are administered traditionally through injection rather than taken orally like most small chemical drugs. Protein pharmaceuticals usually have to be stored under cold conditions or freeze-dried to achieve an acceptable shelf life. To understand and maximize the stability of protein pharmaceuticals or any other usable proteins such as catalytic enzymes, many studies have been conducted, especially in the past two decades. These studies have covered many areas such as protein folding and unfolding/denaturation, mechanisms of chemical and physical instabilities of proteins, and various means of stabilizing proteins in aqueous or solid state and under various processing conditions such as freeze-thawing and drying. This article reviews these investigations and achievements in recent years and discusses the basic behavior of proteins, their instabilities, and stabilization in aqueous state in relation to the development of liquid protein pharmaceuticals.