NMR Studies of Encapsulated Macromolecules

Encapsulation of proteins with reverse micelles has recently been identified as an important new biological NMR application. Encapsulation involves transfer of a hydrated protein into the interior chamber formed within an inverted shell of surfactant (usually dioctyl sulfosuccinate), forming a particle that is dissolved in a low-viscosity solvent, most commonly a short chain alkane. Experimental evidence has demonstrated that macromolecules of significant size and complexity can be encapsulated, and that under appropriate conditions encapsulated molecules retain native structure and biological activity. The tumbling rate of an encapsulated protein is roughly proportional to the bulk viscosity of the solvent, and by selecting an appropriately low viscosity liquid the tumbling rate of an encapsulated molecule may be significantly over that that measured for the free protein in aqueous solution. Such samples may exhibit spectroscopic properties that are superior to those of the free molecules in aqueous solution, and encapsulation thus promises to provide an important enhancement to the resolution and sensitivity of solution NMR experiments. In addition to thebenefits associated with increases in the rate of tumbling, encapsulation has also been shown to be an important biophysical technique that can be used to investigate the influence of environment on proteins. The function of proteins depends not only on the physiochemical attributes of the molecules themselves but also on the local environment in which the molecules are active. Reverse micelle based encapsulation is capable of producing novel environments that serve as a platform for studying the influence of confinement, hydration, ionic strength, and temperature in limits that are beyond the scope of other experimental approaches.