Efficiency of signalling through cytokine receptors depends critically on receptor orientation

The haematopoietic cytokine erythropoeitin in humans is needed for the differentiation and proliferation of precursor cells into red blood cells. It binds and orientates two cell-surface erythropoietin receptors (EPORs) which lead to an intra-cellular phosphorylation cascade. Other erythropoietin-mimetic ligands that dimerize receptors can evoke cellular responses, although less efficiently.