Involvement of Ca²⁺ channel synprint site in synaptic vesicle endocytosis

The synaptic protein interaction (synprint) site of the voltage-gated Ca²⁺channel (VGCC) α1 subunit can interact with proteins involved in exocytosis, and it is therefore thought to be essential for exocytosis of synaptic vesicles. Here we report that the synprint site can also directly bind the μ subunit of AP-2, an adaptor protein for clathrin-mediated endocytosis, in competition with the synaptotagmin 1 (Syt 1) C2B domain. In brain lysates, the AP-2-synprint interaction occurred over a wide range of Ca²⁺ concentrations but was inhibited at high Ca²⁺ concentrations, in which Syt 1 interacted with synprint site. At the calyx of Held synapse in rat brainstem slices, direct presynaptic loading of the synprint fragment peptide blocked endocytic, but not exocytic, membrane capacitance changes. We propose that the VGCC synprint site is involved in synaptic vesicle endocytosis, rather than exocytosis, in the nerve terminal, via Ca ²⁺-dependent interactions with AP-2 and Syt.