Detergent Localization In Model Proteo-bicelles

Abstract

Several methods for crystallization of membrane proteins for structure determination have been published, including those which use discoidal membranes called bicelles. The bicelle-based method has proven to be a stable platform resulting in well-diffracting crystals of G-protein coupled receptors, and other proteins including bacteriorhodopsin. In typical ‘empty’ bicelles - those devoid of protein - long chain phospholipids make up the core of the disk, and micelle-forming detergents “cap” the disk by forming the rim. Short chain phospholipid and cholate analog detergents (e.g. DiC6PC, DHPC and CHAPSO) are included in this “capping” category having been shown to associate preferentially with the bicelle rim. In proteo-bicelles, formed by the mixture of protein-detergent complexes with preformed bicelles, a second type of detergent containing a sugar headgroup (e.g. octylglucoside and maltoside) is introduced. This second type of detergent has proven to be effective in membrane protein purification and stabilization. In this study, we use small angle neutron and x-ray scattering to explore the structure and phase-behavior changes induced by sugar-headgroup type detergents on bicelles and their influence on bicelle-based membrane protein crystallization. Preliminary results suggest that these sugar headgroup amphiphiles partition more heavily into the core of bicelles than their short chain phospholipid and cholate counterparts. An understanding of the roles of these amphiphiles in modifying the meso-structures which eventually lead to crystallization is a critical next step in furthering our understanding of the membrane protein crystallization process in these systems.