Delivery of GPCR Crystals for Serial Femtosecond Crystallography
G protein-coupled receptors (GPCRs) constitute the largest human membrane protein superfamily with over 800 members. They reside in plasma membranes mediating cell signaling and regulating the majority of physiological processes, making them successful targets of about 30–40% of current drugs. Detailed understanding of the mechanism of GPCR action requires high-resolution structural information for many representative members of the family captured in different conformational states, but progress has been limited by the difficulty of preparing large amounts of homogenous and stable samples and by the need for sufficiently large crystals. In this chapter we summarize the work that led to the development and successful application of serial femtosecond crystallography (SFX) to micron-sized GPCR crystals grown and delivered to an X-ray free electron laser (XFEL) beam in a lipid membrane mimetic mesophase, known as lipidic cubic phase (LCP). The LCP-SFX approach obviates the need for growing larger crystals, while also minimizing radiation damage effects on room-temperature samples, and so could substantially shorten the time to success, with concomitant significant reduction in cost and effort. It therefore has the potential to revolutionize structural studies on challenging membrane proteins and their complexes with soluble partners.