Xaperone assisted crystallography of GPCRs: Crystal structure of a Xaperone (blue) stabilizing the active conformation of the ß-2 adrenergic receptor (green). The bound agonist is shown in space filling rendering. CDR1, CDR2 and CDR3 ar depicted in brown, purple and red, respectively.

For all details see: Rasmussen SGF, Choi H.-J., Fung J.-J., Pardon E, Casarosa P, Seok Chae P, DeVree BT, Rosenbaum DM, Thian FS, Kobilka TS, Schnapp A, Konetzki I, Sunahara RK, Gellman SH, Pautsch A, Steyaert J, Weis WI, Kobilka BK (2011). Structure of a nanobody-stabilized active state of the β2 adrenoceptor. Nature 496, 175-180.  See also N&V