Synaptogenesis: New Roles for an Old Player

(A) a2d associates with a1 to regulate the properties of voltage-gated calcium channels. a2d consists of two domains, the extracellular a2 domain and the transmembrane domain d, which are linked by disulfide bonds. Various protein interaction motifs are found on a2. (B) a2d regulates synapse formation and shape independently of voltage-gated calcium channels: a possible model. Thrombospondins, extracellular circles, bind to the VWF interaction motif of a2, causing a conformational change in a2d. This signal is propagated into the cell and perhaps to the extracellular space through another unidentified transmembrane complex. Carl Procko and Shai Shaham