A conserved face of the Jagged/Serrate DSL domain is involved in Notch trans-activation and cis-inhibition

The NMR structure of the Notch binding region of one of its ligands, Jagged, gives insight into the binding surface. Subsequent in vivo analysis of mutants indicates that the same surface is likely to be active in signaling within cells as well as to different cells, and modeling indicates how this surface might interact to participate in such distinct functions. The Notch receptor and its ligands are key components in a core metazoan signaling pathway that regulates the spatial patterning, timing and outcome of many cell-fate decisions. Ligands contain a disulfide-rich Delta/Serrate/LAG-2 (DSL) domain required for Notch trans-activation or cis-inhibition. Here we report the X-ray structure of a receptor binding region of a Notch ligand, the DSL-EGF3 domains of human Jagged-1 (J-1DSL-EGF3). The structure reveals a highly conserved face of the DSL domain, and we show, by functional analysis of Drosophila melanogster ligand mutants, that this surface is required for both cis- and trans-regulatory interactions with Notch. We also identify, using NMR, a surface of Notch-1 involved in J-1DSL-EGF3 binding. Our data imply that cis- and trans-regulation may occur through the formation of structurally distinct complexes that, unexpectedly, involve the same surfaces on both ligand and receptor.