The soluble ligand Y box-1 activates Notch3 receptor by binding to epidermal growth factor like repeats 20-23.

Abstract The transduction of signal by the Notch receptors to the intracellular domain is highly regulated and relies on binding of the ligands to the Epidermal growth factor Like Repeats (ELRs) of receptor's extracellular domain. Both canonical and non-canonical ligands are known to interact with different ELRs and activate Notch receptors. The aim of this study was to investigate the interaction of a soluble non-canonical ligand, Y box-1 (Yb-1) with Notch3 receptor ELRs. Polyclonal antibodies were employed as novel tools to identify the binding site of this ligand. Using various ligand binding and signaling assays, soluble Yb-1 was found to interact specifically with the Notch3 receptor, but not with Notch1. The ELRs 17–24 of Notch3 were identified as the binding site for Yb-1. Further, Yb-1 and Notch3 ELRs 17–24 structures were modelled and the Yb-1-Notch3 interaction interface was predicted to be Notch3 ELRs 20–23. Binding of the Yb-1 with Notch3 ELRs different from those reported for canonical DSL ligands also transduced the signal to the intracellular domain through the negative regulatory region. In conclusion, study highlights the importance of molecular modifications in different Notch3 ELRs for the transduction of signal to the negative regulatory region. [ABSTRACT FROM AUTHOR]