(A) The APP intracellular domain, composed by the two sub-regions JCasp and Ccas, is always cytosolic whether APP molecules are localized at synaptic vesicles or the active zone. (B) Sequences of AID, JCasp, and Ccas used as baits in the proteomic experiments. (C) Brain lysates were incubated for 30 min with 10 μM of either JCasp or ScJCasp. After incubation, the lysates were affinity purified on StrepTactin columns bound to the indicated St-peptides. Bound proteins were analyzed by Western blot. JCasp reduces binding of Syp, Vamp2, and Syt2, but not Ddb1, to St-AID. (D) Triplicate experiment showing that JCasp, but not ScJCasp, significantly reduces binding of Syp, Vamp2, and Syt2 to St-AID. (E) Quantification of the data shown in (D). (F) Hippocampal slices from 8-week-old WT or App-KO mice were stained with an αNeuN (red, left panels) and an αAPP (green middle panel) antibody. The images were merged in the right panels. APP is widely distributed in the hippocampus. The strongest staining is seen in the Hi, MF, CA3, and CA1. The staining for APP is specific since there is no signal in App-KO hippocampi. (G) Staining for APP (red, left panels) and Bassoon (green middle panel) show that APP is expressed in the Stratum radiatum where it partially co-localizes with Bassoon (arrows in the merged image, right panel). Again, the staining for APP and the co-localization spots are specific as shown by their absence in App-KO hippocampi. AID, APP intracellular domain; APP, amyloid precursor protein; WT, wild type.