Synapsins regulate α-synuclein functions.

The normal function of α-synuclein (α-syn) remains elusive. Although recent studies suggest α-syn as a physiologic attenuator of synaptic vesicle (SV) recycling, mechanisms are unclear. Here, we show that synapsin-a cytosolic protein with known roles in SV mobilization and clustering-is required for presynaptic functions of α-syn. Our data offer a critical missing link and advocate a model where α-syn and synapsin cooperate to cluster SVs and attenuate recycling.