Reverse micelle encapsulation as a model for intracellular crowding.

Reverse micelles are discrete nanoscale particles composed of a water core surrounded by surfactant. The amount of water within the core of reverse micelles can be easily manipulated to directly affect the size of the reverse micelle particle. The water loading capacity of reverse micelles varies with temperature, and water can be shed if reverse micelles are exposed to low temperatures. The use of water shedding from the reverse micelle provides precise and comprehensive control over the amount of water available to solvate host molecules. Proteins encapsulated within reverse micelles can be studied to determine the effects of confinement and excluded volume. The data presented here provide an important bridge between commonly employed dilute in vitro studies and studies of the effects of a crowded environment, as found in vivo. Ubiquitin was encapsulated within bis(2-ethylhexyl) sodium sulfosuccinate AOT reverse micelles under various degrees of confinement and was compared with an analogously reconstituted sample of ubiquitin in the commonly used molecular crowding agent bovine serum albumin. The effects of encapsulation were monitored using chemical shift perturbation analysis of the amide (1)H and (15)N resonances. The results also reconcile alternative interpretations of protein cold denaturation within reverse micelles.