Reversible Conjugation of Non-Ionic Detergent Micelles Promotes Partitioning of Membrane Proteins under Non-Denaturing Conditions

Mitra Lal, Ariel University, Ariel, Israel (mitra.31031995@gmail.com)

In the decades’-long quest for high quality membrane protein crystals, non-ionic detergent micelles have primarily served as a passive shield against protein aggregation in aqueous solution and/or as a conformation stabilizing environment. We have focused on exploiting the physical chemistry of detergent micelles in order to direct intrinsic membrane protein/detergent complexes to assemble via conjugation under ambient conditions, thereby permitting finely-tuned control over the micelle cloud point. In the current work, three commercially available amphiphilic, bipyridine chelators in combination with Fe²⁺ or Ni²⁺, were tested for their ability to conjugate non-ionic detergent micelles both in the presence and absence of an encapsulated bacteriorhodopsin molecule. Water-soluble chelators were added and results monitored with light microscopy and dynamic light scattering. [Bipyridine:metal] complexes produced micellar conjugates which appeared as oil-rich globules (10-200 µm) in the light microscope. Dynamic light scattering analysis demonstrated that micellar conjugation is complete 20 minutes after introduction of the amphiphilic complex and that the conjugation process can be fully or partially reversed with water soluble chelators. This process of controlled conjugation/deconjugation under nondenaturing conditions provides broader flexibility in the choice of detergent for intrinsic membrane protein purification as well as conformational flexibility during the crystallization procedure.