If you thought that all it took to kick-start a signaling pathway was a ligand binding to a receptor, think again. How and when that binding occurs, it turns out, is what determines what happens inside the cell. In linkurl:a study;http://www.cell.com/content/article/fulltext?uid=PIIS0092867408000470 published online in Cell today, Sherry LaPorte of Stanford University and colleagues describe the structure of the Interleukin-4 and Interleukin-13 (IL-4/13) cytokines and the complete set of receptors they bind, including the one receptor complex they have in common. It's not very surprising that different ligands can act on the same receptor to trigger different signal cascades. But the authors' crystal structures reveal that identical receptors can distinguish between ligands that differ only slightly, such as the IL4 and IL-13 molecules. The receptor that IL-4 and IL-13 share is actually a composite of two receptors: the IL-14 receptor α and the IL-13 receptor α. Both are required to initiate...
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