Reverse Micelle Encapsulation as a Model for Intracellular Crowding

Abstract

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.

Simulations of the confinement of ubiquitin in self-assembled reverse micelles

“…Flynn and co-workers have argued that the loss of resonances in the Ile44 region is due to interactions of ubiquitin with AOT headgroups. 16,68 The interaction between proteins and AOT RM has been previously shown to denature proteins. 63,69 Recent studies of ubiquitin in supercooled water failed to see cold denaturation of ubiquitin down to −32…”

“…Confined waters in RMs have been proposed to mimic confined waters in biological systems. 16 The size of RMs depends on the water to surfactant ratio, w 0 , which can be well controlled to alter the confinement and hydration level. 17 Depending on the choice of surfactant, the protein may not maintain the folded structure when encapsulated in a RM.…”

Protein Stability in Reverse Micelles

“…Chemical interactions between the group on the interior of the micelle and the test protein also do not wholly explain the effects on encapsulation. As pointed out by Va nHorn et al, [22] the geometry of the chemical interactions may play ar ole.W hereas the cosolute models of the surfactant head groups can approach the protein from any angle,i nr everse micelles,t he protein is faced with ac oncave surface with aradius almost matching its convex surface.Furthermore,the confined water molecules may play amajor role because this water is strongly affected by the micelle-protein interface. [10] Opposite observations,s hifts to higher T s and DG 0 0 u T ðÞ values,have been observed in high concentration of synthetic polymers and protein crowders.…”

Facile synthesis of amorphous Ni(OH)2 for high-performance supercapacitors via electrochemical assembly in a reverse micelle

“…Reverse micelle solutions are homogeneous/isotropic systems which consists of three different phase in thermodynamics equilibrium, namely water droplets stabilized in a continuous oil phase with the assistance of a surrounding monolayer of preferentially aligned surfactants and cosurfactants [43,44]. They have been demonstrated to be a special media for its feasibility in controlling the size and shape along with the monodispersity of the nanomaterials assembled on electrode substrates [45,46].…”