Serial Femtosecond Crystallography of G Protein-Coupled Receptors.

G protein-coupled receptors (GPCRs) represent a large superfamily of membrane proteins that mediate cell signaling and regulate a variety of physiological processes in the human body. Structure-function studies of this superfamily were enabled a decade ago by multiple breakthroughs in technology that included receptor stabilization, crystallization in a membrane environment, and microcrystallography. The recent emergence of X-ray free-electron lasers (XFELs) has further accelerated structural studies of GPCRs and other challenging proteins by overcoming radiation damage and providing access to high-resolution structures and dynamics using micrometer-sized crystals. Here, we summarize key technology advancements and major milestones of GPCR research using XFELs and provide a brief outlook on future developments in the field.