Dispersion and Interaction of Charged Fluorescent Dyes in Protein‐Polymer Surfactant‐based Non‐Aqueous Liquid

An atomistic view of solvent-free protein liquids: the case of Lipase A

Solvent-free enzymes hold the promise of being able to deliver higher activity at elevated temperatures by virtue of them being not limited by the boiling point of the solvent. They have been realized in the liquid phase through a polymer surfactant coating on the protein surface. However, a clear understanding of intermolecular interactions, structure, dynamics, and the behaviour of the minuscule amount of water present in the solvent-free protein liquid is essential to enhance the activity of these biofluids. Using atomistic molecular dynamics simulations, we demonstrate that the scaled spatial correlations between proteins in the hybrid liquid phase of Lipase A enzymes are comparable to the inter-particle correlations in a noble gas fluid. The hydrophilic region of the surfactants forms a coronal layer around each enzyme which percolates throughout the liquid, while the hydrophobic parts are present as disjointed clusters. Inter-surfactant interactions, determined to be attractive and in the range of -200 to -300 kcal mol^-1, stabilize the liquid state. While the protein retains its native state conformational dynamics in the solvent-free form, the fluxionality of its side chains is much reduced; at 333 K, the latter is found to be equivalent to that of the enzyme in an aqueous solution at 249 K. Despite the sluggishness of the solvent-free enzyme, some water molecules exhibit high mobility and transit between enzymes primarily via the interspersed hydrophilic regions. These microscopic insights offer ideas to improve substrate diffusion in the liquid to enable the enhancement of catalytic activity.

Solvent-free liquid avidin as a step toward cold chain elimination

The temperature sensitivity of vaccines and therapeutic proteins forces the distribution of life-saving treatments to rely heavily on the temperature-controlled (usually 2-8°C) supply and distribution network known as the cold chain. Here, using avidin as a model, we demonstrate how surface engineering could significantly increase the thermal stability of therapeutic proteins. A combination of spectroscopic (Fourier transform infrared, circular dichroism, and ultraviolet-visible) and scattering techniques (dynamic light scattering, small-angle, and wide-angle X-ray scattering) were deployed to probe the activity, structure, and stability of the model protein. Temperature-dependent synchrotron radiation circular dichroism spectroscopy was used to demonstrate a significant increase in thermal stability, with a half denaturation temperature of 139.0°C and reversible unfolding with modified avidin returning to a 90% folded state when heated to temperatures below 100°C. Accelerated aging studies revealed that modified avidin retained its secondary structure after storage at 40°C for 56 days, equivalent to 160 days at 25°C. Furthermore, binding studies with multiple ligands revealed that the binding site remained functional after modification. As a result, this approach has potential as a storage technology for therapeutic proteins and the elimination of the cold chain, enabling the dissemination of life-saving vaccines worldwide.