SASH1: A Novel Eph Receptor Partner and Insights into SAM-SAM Interactions.

[Display omitted] • SASH1 is identified as a novel binding partner for Eph receptors through SAM-SAM interactions, with the highest affinity for EphA8. • The high-resolution crystal structure of the EphA8/SASH1 SAM-SAM complex reveals molecular basis governing the specific inter-molecular interactions. • Cancer mutations (EphA8 R942H or G978D) impair the interaction between EphA8 and SASH1, highlighting potential implications in tumorigenesis. • SASH1 enhances EphA8 receptor kinase activation through their SAM-SAM interaction. The Eph (erythropoietin-producing human hepatocellular) receptor family, the largest subclass of receptor tyrosine kinases (RTKs), plays essential roles in embryonic development and neurogenesis. The intracellular Sterile Alpha Motif (SAM) domain presents a critical structural feature that distinguishes Eph receptors from other RTKs and participates in recruiting and binding downstream molecules. This study identified SASH1 (SAM and SH3 domain containing 1) as a novel Eph receptor-binding partner through SAM-SAM domain interactions. Our comprehensive biochemical analyses revealed that SASH1 selectively interacts with Eph receptors via its SAM1 domain, displaying the highest affinity for EphA8. The high-resolution crystal structure of the EphA8-SASH1 complex provided insights into the specific intermolecular interactions between these proteins. Cellular assays confirmed that EphA8 and SASH1 co-localize and co-precipitate in mammalian cells, with cancer mutations (EphA8 R942H or G978D) impairing this interaction. We demonstrated that SAM-SAM interaction is critical for SASH1-mediated regulation of EphA8 kinase activity, shedding new light on the Eph signaling pathway and expanding our understanding of the molecular basis of the tumor suppressor gene SASH1. [ABSTRACT FROM AUTHOR]