Physicochemical Insights into the Stabilization of Stressed Lysozyme and Glycine Homopeptides by Sorbitol

Stability and Fibrillation of Lysozyme in the Mixtures of Ionic Liquids with Varying Hydrophobicity

Combinatorial effects of small molecules provide newer avenues to improve protein stability. The combined effect of two different classes of ILs on the stability and fibrillation propensity of lysozyme (Lyz) was investigated. Imidazolium-ILs (an aromatic moiety) with varying alkyl chains, methyl (MIC), butyl (BMIC) and hexyl (HMIC), and pyrrolidinium-IL (alicyclic moiety) with butyl substitution (BPyroBr) were chosen. The fibrillation was delayed by the addition of any of the IL. While added as a mixture with varying molar ratios, the presence of HMIC with MIC or BMIC at the ratio of 2:1 increased the fibrillation time synergistically by increasing lag time and reducing elongation rate. The protein stability was significantly reduced in these conditions compared to lower molar ratios of HMIC with MIC or BMIC. Molecular dynamics simulation studies indicated that upon adding Im-ILs water molecules were reduced around Lyz, whereas BPyroBr slightly increased the water around Lyz. Preferential interaction studies suggest that the preferential binding of HMIC with the protein was the most favored and it synergistically facilitated the preferential binding of MIC. Though BMIC was preferentially binding to the protein, it disfavoured the interaction of MIC. BMIC and BPyroBr had a competitive binding on the surface of Lyz. The results suggested that the mixture of ILs containing the longer alkyl chain destabilizes the protein and delays the fibril formation to a larger extent than the shorter alkyl chain ILs. Further, the effect of aromatic ILs could be greater than alicyclic ILs having the same alkyl chain length.

Deciphering the spectroscopic and thermodynamic aspects of binding of biologically important antioxidants with the alkali induced state of human serum albumin

Protein-ligand interactions are crucial for developing and identifying novel therapeutic targets. In this study, we investigate the interaction of the alkali induced state of human serum albumin (pH 11.2) with three hydroxycinnamic acid derivatives (HCDs), ferulic acid (FA), sinapic acid (SA) and trans-o-coumaric acid, which are biologically important antioxidants, and compare the outcomes with the results obtained at physiological pH (7.4). This study aims to explore the interaction of altered protein conformation with small molecules. Spectroscopic characterization methods show that the conformation of HSA and the ionic properties of HCDs are pH-dependent. Fluorescence, FRET and lifetime measurements reveal that the binding of HCDs with HSA is different at both pH 7.4 and 11.2. Despite the moderate binding of HCDs to HSA, circular dichroism and thermal denaturation studies report no conformational changes in HSA in the presence of HCDs. Isothermal titration calorimetry is employed to assess their binding based on structure and energetics using thermodynamic parameters. Standard molar enthalpy change (ΔH0m) and standard molar entropy change (ΔS0m) values vary with the change of pH from 7.4 to 11.2 with the contributions from the exothermicity and hydrophobicity of functional and aromatic groups of HCDs. Ferulic acid (FA) and sinapic acid (SA) binding to HSA is entropically driven, whereas trans-o-coumaric acid (CA) acid binding is enthalpically favourable. Our ITC studies also reveal that the involvement of -OH functional groups present in CA in binding with HSA is greater than that present in FA and SA at pH 11.2. Overall, this experimental study shows the comparable binding strength of HCDs to both the alkali-induced state of HSA and native HSA (pH 7.4). However, the mechanism of their binding is different.

pH-dependent interactions of biologically important metal ions with hen egg white lysozyme based on its hydration properties: Thermodynamic and mechanistic insights

Importance of metal ion selectivity in biomolecules and their key role in proteins are widely explored. However, understanding the thermodynamics of how hydrated metal ions alter the protein hydration and their conformation is also important. In this study, the interaction of some biologically important Ca2+, Mn2+, Co2+, Cu2+, and Zn2+ ions with hen egg white lysozyme at pH 2.1, 3.0, 4.5 and 7.4 has been investigated. Intrinsic fluorescence studies have been employed for metal ion-induced protein conformational changes analysis. Thermostability based on protein hydration has been investigated using differential scanning calorimetry (DSC). Thermodynamic parameters emphasizing on metal ion-protein binding mechanistic insights have been well discussed using isothermal titration calorimetry (ITC). Overall, these experiments have reported that their interactions are pH-dependent and entropically driven. This research also reports the strongly hydrated metal ions as water structure breaker unlike osmolytes based on DSC studies. These experimental results have highlighted higher concentrations of different metal ions effect on the protein hydration and thermostability which might be helpful in understanding their interactions in aqueous solutions.

Targeting disorders in unstructured and structured proteins in various diseases

Intrinsically disordered proteins (IDPs) and intrinsically disordered protein regions (IDPRs) are proteins and protein segments that usually do not acquire well-defined folded structures even under physiological conditions. They are abundantly present and challenge the "one sequence-one structure-one function" theory due to a lack of stable secondary and/or tertiary structure. Due to conformational flexibility, IDPs/IDPRs can bind with multiple interacting partners with high-specificity and low-affinity and perform essential biological functions associated with signalling, recognition and regulation. Mis-functioning and mis-regulation of IDPs and IDPRs causes disorder in disordered proteins and disordered protein segments which results in numerous human diseases, such as cancer, Parkinson's disease (PD), Alzheimer's disease (AD), diabetes, metabolic disorders, systemic disorders and so on. Due to the strong connection of IDPs/IDPRs with human diseases they are considered potentential targets for drug therapy. Since they disobey the "one sequence-one structure-one function" concept, IDPs/IDPRs are complex systems for drug targeting. This review summarises various protein disorder diseases and different methods for therapeutic targeting of disordered proteins/segments. Targeting IDPs/IDPRs for diseases will open up a new era of rational drug design and drug discovery.

Stabilization of enzymes via immobilization: Multipoint covalent attachment and other stabilization strategies

The use of enzymes in industrial processes requires the improvement of their features in many instances. Enzyme immobilization, a requirement to facilitate the recovery and reuse of these water-soluble catalysts, is one of the tools that researchers may utilize to improve many of their properties. This review is focused on how enzyme immobilization may improve enzyme stability. Starting from the stabilization effects that an enzyme may experience by the mere fact of being inside a solid particle, we detail other possibilities to stabilize enzymes: generation of favorable enzyme environments, prevention of enzyme subunit dissociation in multimeric enzymes, generation of more stable enzyme conformations, or enzyme rigidification via multipoint covalent attachment. In this last point, we will discuss the features of an "ideal" immobilization protocol to maximize the intensity of the enzyme-support interactions. The most interesting active groups in the support (glutaraldehyde, epoxide, glyoxyl and vinyl sulfone) will be also presented, discussing their main properties and uses. Some instances in which the number of enzyme-support bonds is not directly related to a higher stabilization will be also presented. Finally, the possibility of coupling site-directed mutagenesis or chemical modification to get a more intense multipoint covalent immobilization will be discussed.

Unraveling diverse action of triton X-100 and methimazole on lysozyme fibrillation/aggregation: Physicochemical insights

Identification of functionalities responsible for prevention of fibrillation in proteins is important to design effective drugs in addressing neurodegenerative diseases. We have used nonionic surfactant triton X-100 (TX-100) and antithyroid drug methimazole (MMI) to understand mechanistic aspects of action of these molecules having different functionalities on hen egg-white lysozyme at different stages of fibrillation. After establishing the nucleation, elongation and maturation stages of fibrillation of protein at 57 °C, energetics of interactions with these molecules have been determined by using isothermal titration calorimetry. Differential scanning calorimetry has permitted assessment of thermal stability of the protein at these stages, with or without these molecular entities. The enthalpies of interaction of TX-100 and MMI with protein fibrils suggest importance of hydrogen bonding and polar interactions in their effectiveness towards prevention of fibrils. TX-100, in spite of several polar centres, is unable to prevent fibrillation, rather it promotes. MMI is able to establish polar interactions with interacting strands of the protein and disintegrate fibrils. A rigorous comparison with inhibitors reported in literature highlights importance -OH and >CO functionalities in fibrillation prevention. Even though MMI has hydrogen bonding centres, its efficiency as inhibitor falls after the inhibited lysozyme fibrils further interact and form amorphous aggregates.