Tion process. 3. Adrenergic Receptor Structures. In 2007, the report of the X-ray structure for the human 2-adrenengic receptor marked a breakthrough in the structural study of liganded GPCRs. The structure was solved by two different techniques (Rasmussen et al., 2007; Rosenbaum et al., 2007). In one approach, an antibody Fv fragment?2-adrenergic receptor complex was generated that yielded low-or