Osmotic pressure method to measure salt induced folding/unfolding of bovine serum albumin

Macromolecular condensation buffers intracellular water potential

Optimum protein function and biochemical activity critically depends on water availability because solvent thermodynamics drive protein folding and macromolecular interactions1. Reciprocally, macromolecules restrict the movement of 'structured' water molecules within their hydration layers, reducing the available 'free' bulk solvent and therefore the total thermodynamic potential energy of water, or water potential. Here, within concentrated macromolecular solutions such as the cytosol, we found that modest changes in temperature greatly affect the water potential, and are counteracted by opposing changes in osmotic strength. This duality of temperature and osmotic strength enables simple manipulations of solvent thermodynamics to prevent cell death after extreme cold or heat shock. Physiologically, cells must sustain their activity against fluctuating temperature, pressure and osmotic strength, which impact water availability within seconds. Yet, established mechanisms of water homeostasis act over much slower timescales2,3; we therefore postulated the existence of a rapid compensatory response. We find that this function is performed by water potential-driven changes in macromolecular assembly, particularly biomolecular condensation of intrinsically disordered proteins. The formation and dissolution of biomolecular condensates liberates and captures free water, respectively, quickly counteracting thermal or osmotic perturbations of water potential, which is consequently robustly buffered in the cytoplasm. Our results indicate that biomolecular condensation constitutes an intrinsic biophysical feedback response that rapidly compensates for intracellular osmotic and thermal fluctuations. We suggest that preserving water availability within the concentrated cytosol is an overlooked evolutionary driver of protein (dis)order and function.

Application of the multisolute osmotic virial equation to solutions containing electrolytes

The prediction of multisolute solution behavior of solutions containing electrolytes is important in many areas of research, including cryopreservation. In this study, the use of a novel form of the osmotic virial equation for multisolute solutions containing an electrolyte is investigated and compared to a rigorous electrolyte solution theory, the Pitzer-Debye-Huckel equation. For aqueous solutions containing a small molecule (either dimethyl sulfoxide or glycerol) and sodium chloride, the multisolute osmotic virial equation, which utilizes only two parameters to capture the electrolyte solution behavior, is shown to be as accurate as the Pitzer-Debye-Huckel equation, which utilizes six empirical parameters and multiple functions to capture the electrolyte solution behavior. In addition, an approach based on the multisolute osmotic virial equation to investigate the effect of electrolyte concentration on macromolecule solution behavior is presented and applied to aqueous solutions of hydroxyethyl starch and sodium chloride. The multisolute osmotic virial equation is shown to be an accurate, straightforward predictive solution theory for important multisolute solutions containing electrolytes.

Synthesis of gold microplates using bovine serum albumin as a reductant and a stabilizer

Gold microplates were synthesized in aqueous solutions by reducing HAuCl(4) with the hydroxyl groups in both serine and threonine of bovine serum albumin (BSA), which is a globular protein in its native state. In this article, we systematically investigated the effects of temperature, pH value, the concentration of BSA, and ionic species on the reduction kinetics and thus the size and morphology of the final product. The optimal experimental conditions for producing uniform Au microplates include the following: an elevated temperature in the range of 55-65 degrees C, an acidic solution with pH approximately 3, and the presence of NaCl (0.14 M). We found that if any one of these parameters was deviated from the optimal condition, Au microplates would not be formed in high yields. We also found that the surfaces of the as-synthesized Au microplates were covered by a dense array of BSA bumps.

Water Compartments in Cells

Human experience in the macrobiological world leads scientists to visualize water compartments in cells analogous to the bladder in the human pelvis or ventricles in the brain. While such water-filled cellular compartments likely exist, the volume contributions are insignificant relative to those of biomolecular hydration compartments. The purpose of this chapter is to identify and categorize the molecular water compartments caused by proteins, the primary macromolecular components of cells. The categorical changes in free energy of water molecules on proteins cause these compartments to play dominant roles in osmoregulation and provide important adjuncts to fundamental understanding of osmosensing and osmosignaling mechanisms. Water compartments possess differences in molecular motion, enthalpy, entropy, freezing point depression, and other properties because of electrostatic interaction of polar water molecules with electric fields generated by covalently bound pairs of opposite charge caused by electronegative oxygen and nitrogen atoms of the protein. Macromolecules, including polypeptides, polynucleotides, and polysaccharides, are stiff molecular chains with restricted folding capacities due to inclusion of rigid ring structures or double amide bonds in the backbone sequence. This creates "irreducible spatial charge separation" between positive and negative partial charges, causing elevated electrostatic energy. In the fully hydrated in vivo state of living cells the high dielectric coefficient of water reduces protein electrostatic free energy by providing polar "water bridge networks" between charges, thereby creating four measurably different compartments of bound water with distinct free energy differences.

The state of water in biological systems

This paper addresses the issue of how the aqueous cytoplasm is organized on a macroscopic scale. Mitochondria were used as the experimental model, and a unique experimental approach was used to probe the properties of water in the mitochondrial matrix. The results demonstrate aqueous phase separation into two distinct phases with different osmotic activity and different solute partition coefficients. The larger phase, designated "normal water," is osmotically active and behaves in every respect like a bulk, dilute salt solution. The smaller phase, designated "abnormal water," is osmotically inactive and comprises the water of hydration of matrix proteins. It is, nevertheless, solvent water, with highly selective partition coefficients, and behaves like a Lewis base.

Physicochemical and immunochemical properties of recombinant human serum albumin from Pichia pastoris

We analyzed and compared the physicochemical and immunochemical properties of recombinant human serum albumin (rHSA) from Pichia pastoris with those of plasma-derived human serum albumin (pHSA). The second virial coefficient of rHSA, obtained from colloid osmotic pressure measurements at pH 6.7 +/- 0.1 was not significantly different from that of pHSA (P > 0.05). A 25% rHSA solution exhibited Newtonian flow, and the viscosity of 25% rHSA at 20 +/- 0.02 degrees C was not significantly different from that of 25% pHSA (P > 0.05). We analyzed the long- and medium-chain fatty acid composition of rHSA by reverse-phase HPLC using 9-anthryldiazomethane as the fluorescent labeling reagent. The total amount of fatty acid was higher for pHSA than for rHSA. The fatty acid composition of the rHSA preparation was the same as that of the pHSA preparation. However, the amounts of palmitic acid (C16:0) and stearic acid (C18:0) in rHSA were much lower than those in pHSA. Interestingly, we found that P. pastoris produced linolenic acid (C18:3) because it was detected in rHSA. The immunochemical properties of rHSA were analyzed by a parallel line assay method using anti-pHSA polyclonal antibody, and were identical to those of pHSA (P > 0.05).