Cells use cytokines to communicate with each other in various complex processes, ranging from cell proliferation and differentiation to apoptosis and immune responses. These small soluble proteins recognize their target cells via specific cell surface receptors. Our laboratory is interested in dissecting the underlying molecular mechanisms of signal transduction by using an integrative structural biology approach. Employing state of the art cryo-EM will allow us to determine high-resolution structures of such receptor-ligand complexes. Defining different functional states, using other structural, biochemical and biophysical methods such as protein engineering, will help us to understand and manipulate selected signaling pathways, with putative pharmaceutical implications.