Alteration of water absorption in the THz region traces the onset of fibrillation in proteins

Peculiarities of the Dynamical Hydration Shell of Native Conformation Protein Using a Bovine Serum Albumin Example

This paper describes an approach based on the method of terahertz time-domain spectroscopy, which allows the analysis of dynamical hydration shells of proteins with a thickness of 1-2 nm. Using the example of bovine serum albumin in three conformations, it is shown that the hydration shells of the protein are characterized by increased binding of water molecules in the primary hydration layers, and in more distant areas of hydration, on the contrary, the water structure is somewhat destroyed. The fraction of free or weakly bound molecules, usually observed in the structure of liquid water in hydration shells, become more numerous but its average binding is greater than in undisturbed water. The energy distribution of hydrogen bonds in hydration shells is narrowed compared to undisturbed water. All these manifestations of hydration are most pronounced for the native conformation of the protein. Also, the hydration shells of the native protein are characterized by a smaller number of hydrogen bonds and a tendency to decrease their average energy compared to non-native conformations. The fact of a pronounced peculiarity of the hydration shells of the protein in the native conformation has been noted for different proteins before. However, the methodological approach used in this work for the first time allowed this peculiarity to be described by specific parameters of the intermolecular structure and dynamics of water.

Sugar Molecules Inhibit Insulin Aggregation: A Decisive Role Being Played by the Protein Solvation Energetics

Insulin plays vital roles in controlling blood sugar level in the human body. However, it sometimes aggregates during the storage, and its efficacy (on the treatment of diabetes II disease) reduces significantly. So, understanding the insulin aggregation could help in long-term storage. Here we investigate the amyloid growth of human insulin protein in the presence of sugar molecules and observe that glucose and sucrose delay the insulin aggregation, the effect being systematically sugar dependent. We then investigate protein hydration during the aggregation process using terahertz spectroscopy, as the hydration plays a pioneering role in maintaining biological systems. Our study infers that the water network changes systematically with protein conformations and solvation entropy-enthalpy balance plays a decisive role in the aggregation process.

Terahertz spectroscopy as a method for investigation of hydration shells of biomolecules

The hydration of biomolecules is one of the fundamental processes underlying the construction of living matter. The formation of the native conformation of most biomolecules is possible only in an aqueous environment. At the same time, not only water affects the structure of biomolecules, but also biomolecules affect the structure of water, forming hydration shells. However, the study of the structure of biomolecules is given much more attention than their hydration shells. A real breakthrough in the study of hydration occurred with the development of the THz spectroscopy method, which showed that the hydration shell of biomolecules is not limited to 1-2 layers of strongly bound water, but also includes more distant areas of hydration with altered molecular dynamics. This review examines the fundamental features of the THz frequency range as a source of information about the structural and dynamic characteristics of water that change during hydration. The applied approaches to the study of hydration shells of biomolecules based on THz spectroscopy are described. The data on the hydration of biomolecules of all main types obtained from the beginning of the application of THz spectroscopy to the present are summarized. The emphasis is placed on the possible participation of extended hydration shells in the realization of the biological functions of biomolecules and at the same time on the insufficient knowledge of their structural and dynamic characteristics.

Thermo-Resistive Phase Behavior of Trivalent Ion-Induced Microscopic Protein-Rich Phases: Correlating with Ion-Specific Protein Hydration

Proteins, in the presence of trivalent cations, exhibit intriguing phase behavior which is contrasting compared to mono- and divalent cations. At room temperature (RT), trivalent cations induce microscopic liquid-liquid phase separation (LLPS) in which a protein-rich phase coexists with a dilute phase. The critical solution temperature related phenomena in these complex fluids are well studied; however, such studies have mostly been restricted below the denaturation temperature (T_M) of the protein(s) involved. Here, we probe the phase behavior of bovine serum albumin (BSA) incubated at 70 °C (>T_M) in the presence of Na⁺, Mg²⁺, La³⁺, Y³⁺, and Ho³⁺ ions. BSA in the presence of mono- and bivalent ions forms an intense gel phase at 70 °C; however, the trivalent salts offer remarkable thermal resistivity and retain the fluid LLPS phase. We determine the microscopic phase behavior using differential interference contrast optical microscopy, which shows that the LLPS droplet structures in the M³⁺ ion-containing protein solutions prevail upon heating, whereas Mg²⁺ forms composed cross-linking gelation upon thermal incubation. We probe the interior environment of the protein aggregates by ps-resolved fluorescence anisotropy measurements using 8-anilino-1-naphthalenesulfonic acid (ANS) as an extrinsic fluorophore. It reveals that while the LLPS phase retains the rotational time constants upon heating, in the case of gelation, the immediate environment of ANS gets significantly perturbed. We investigate the explicit protein hydration at RT as well as at T > T_M using the ATR THz-FTIR (1.5-22.5 THz) spectroscopy technique and found that hydration shows strong ion specificity and correlates the phase transition behavior.

Excipients Do Regulate Phase Separation in Lysozyme and Thus Also Its Hydration

While the liquid-liquid phase separation (LLPS) process in proteins has been studied in great detail, it has not been widely explored how the associated protein hydration changes during the process and how crucial its role is in the process itself. In this contribution, we experimentally explore the alteration of lysozyme hydration during its LLPS process using attenuated total reflection (ATR)-FTIR spectroscopy in the THz frequency region (1.5-21 THz). Additionally, we explore the role of excipients (l-arginine, sucrose, bovine albumin (BSA), and ubiquitin (Ubi)) in regulating the process and found that, while sucrose stabilizes the LLPS, BSA inhibits it. The effect of Arg in the LLPS is subtle, and that of Ubi is concentration dependent. We made a detailed analysis of the hydration profile of Lys in the presence of these excipients and observe that a change in hydration in terms of H-bond making/breaking is a definite signature regulating the process.

Hydration Dynamics in Biological Membranes: Emerging Applications of Terahertz Spectroscopy

Water drives the spontaneous self-assembly of lipids and proteins into quasi two-dimensional biological membranes that act as catalytic scaffolds for numerous processes central to life. However, the functional relevance of hydration in membrane biology is only beginning to be addressed, predominantly because of challenges associated with direct measurements of hydration microstructure and dynamics in a biological milieu. Our recent work on the novel interplay of membrane electrostatics and crowding in shaping membrane hydration dynamics utilizing terahertz (THz) spectroscopy represents an important step in this context. In this Perspective, we provide a glimpse into the ever-broadening functional landscape of hydration dynamics in biological membranes in the backdrop of the unique physical chemistry of water molecules. We further highlight the immense (and largely untapped) potential of the THz toolbox in addressing contemporary problems in membrane biology, while emphasizing the adaptability of the analytical framework reported recently by us to such studies.