Controlling membrane protein folding with light illumination and catanionic surfactant systems.

摘要

Membrane proteins are of significant importance, performing a variety of biological functions including pumps, channels, and receptors. Thus, membrane proteins represent attractive candidates as drug targets. Bacteriorhodopsin (bR), the most widely studied membrane protein, consists of seven transmembrane helical segments and functions which can work as a proton pump in Halobacterium Salinarium. In the present study, the reversible control of bR conformation with simple light illumination is examined, providing a protocol to probe membrane protein folding (a challenge even to this day due to the large, aggregation-prone hydrophobic regions of membrane proteins compared to soluble proteins). Two general methodologies are utilized to control membrane protein folding, including (1) saturation of the natural lipids with a photoresponsive surfactant resulting in partitioning of the protein into detergent-lipid mixed micelles in the unfolded state, and (2) the development of artificial bilayers through self-assembly of the photosurfactant into light-responsive vesicles to solubilize membrane proteins. The azobenzene-based photosurfactant undergoes a reversible photoisomerization upon illumination either visible ( trans) or UV (cis) light. The trans isomer is relatively hydrophobic and, thus, readily forms detergent-lipid mixed micelles relative to the cis form, while the planar trans conformation also enhances the formation of artificial lamellar structures in vesicle bilayers relative to the bent cis form. Together, these strategies provide a convenient means to control membrane protein folding with light illumination.