The structure of EPO-R in the absence and presence of an activating ligand. The α-carbon trace of the extracellular domain of EPO receptor in the absence (A) and presence (B) of an activating EPO mimetic peptide (EMP) is shown, along with a cartoon representation of the intracytoplasmic events that ensue upon ligand binding. J2i indicates inactive JAK2; J2a, active JAK2. Adapted from Livnah et al²⁴  and reproduced with permission. Copyright 1999 AAAS.