Structural basis for the interaction of the free SH2 domain EAT-2 with SLAM receptors in hematopoietic cells

The T and natural killer (NK) cell-specific gene SAP (SH2D1A) encodes a 'fr ee SH2 domain' that binds a specific tyrosine motif in the cytoplasmic tail of SLAM (CD150) and related cell surface proteins. Mutations in SH2D1A cau se the X-linked lymphoproliferative disease, a primary immunodeficiency. He re we report that a second gene encoding a free SH2 domain, EAT-2, is expre ssed in macrophages and B lympho cytes. The EAT-2 structure in complex with a phosphotyrosine peptide containing a sequence motif with Tyr281 of the c ytoplasmic tail of CD150 is very similar to the structure of SH2D1A complex ed with the same peptide. This explains the high affinity of EAT-2 for the pTyr motif in the cytoplasmic tail of CD150 but, unlike SH2D1A, EAT-2 does not bind to non-phosphorylated CD150. EAT-2 binds to the phosphorylated rec eptors CD84, CD150, CD229 and CD244, and acts as a natural inhibitor, which interferes with the recruitment of the tyrosine phosphatase SHP-2. We conc lude that EAT-2 plays a role in controlling signal transduction through at least four receptors expressed on the surface of professional antigen-prese nting cells.