UNDERSTANDING MEMBRANE PROTEIN CRYSTALLIZATION IN THE BICELLE SYSTEM

Illinois Institute Of Technology, Chicago IL

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. 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 phospholipids 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 head group (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 look used small angle x-ray scattering to complement work previously done with neutron scattering in exploring the structure and phase-behavior changes induced by sugar-head group type detergents on bicelles and their influence on bicelle-based membrane protein crystallization. Preliminary results suggest that these sugar head group detergents localize homogeneously in the aggregate, as well as elongate the aggregate. An understanding of the roles of these amphiphiles in modifying the meso-structures that eventually lead to crystallization is a critical next step in furthering our understanding of the membrane protein crystallization process in these systems.