Abstract

With the advent of the recent determination of high-resolution crystal structures of bovine rhodopsin and human β2 adrenergic receptor (β2AR), there are still many structure-function relationships to be learned from other G protein- coupled receptors (GPCRs). Many of the pharmaceutically interesting GPCRs cannot be modeled because of their amino acid sequence divergence from bovine rhodopsin and β2AR. Structure determination of GPCRs can provide new avenues for engineering drugs with greater potency and higher specificity. Several obstacles need to be overcome before membrane protein structural biology becomes routine: over-expression, solubilization, and purification of milligram quantities of active and stable GPCRs. Coordinated iterative efforts are required to generate any significant GPCR overexpression. To formulate guidelines for GPCR purification efforts, we review published conditions for solubilization and purification using detergents and additives. A discussion of sample preparation of GPCRs in detergent phase, bicelles, nanodiscs, or low-density lipoproteins is presented in the context of potential structural biology applications. In addition, a review of the solubilization and purification of successfully crystallized bovine rhodopsin and β2AR highlights tools that can be used for other GPCRs.