Characterization of the 10MAG/LDAO reverse micelle surfactant system, a useful tool for studying protein biophysics.

Abstract

Reverse micelles (RMs) are spontaneously organizing nanobubbles composed of an organic solvent, surfactants, and an aqueous phase that can encapsulate biological macromolecules. Reverse micelles can facilitate novel biophysical studies, especially studies of confinement and interfacial interactions on protein thermodynamics. The 1-decanoyl-rac-glycerol (10MAG) and lauryldimethylamine-N-oxide (LDAO) surfactant system provides long-term protein sample stability without precise optimization of RM size, which is determined by the ratio of water to surfactant, known as water loading, W0. In this study, we investigated this unique property of 10MAG/LDAO by encapsulating three model proteins- cytochrome c, myoglobin, and flavodoxin, to observe changes in the system using dynamic light scattering (DLS), diffusion ordered nuclear magnetic resonance spectroscopy (DOSY NMR), and NMR T1 relaxation measurements. We found that this surfactant system differs greatly from the traditional, monodisperse RM population model. At all conditions, 10MAG/LDAO RMs exist in thermodynamic equilibrium with a large, nonspherical bulk-like water reservoir. Moreover, proteins seem to drive the thermodynamics of the mixture, encapsulating at their optimal RM size. These findings are important for developing thermodynamic models to complement applications of 10MAG/LDAO RMs for studying protein stability and water dynamics in the nanoconfined space.