Much more than the sum of the parts: structures of the dual SH2 domains of ZAP-70 and Syp

Proteins involved in signaling pathways frequently contain one or more SH2 domains. New structural information on proteins that carry two SH2 domains show, surprisingly, that the domains are closely interlinked, so the binding sites are rigidly oriented with respect to each other. Thus, only ligands with the right spacing of the phosphotyrosines will be tightly bound.