Synaptic ribbons (SRs) are the presynaptic hallmark of sensory ribbon synapses. SRs tether up to several hundred synaptic vesicles (SVs) to support continuous exocytosis. How tethering of SVs to SRs is achieved is currently unknown. We previously demonstrated that Piccolino, an integral component of SRs1,2, binds to RIBEYE, the main component of SRs, via its C-terminus3. Here, we explore how the N-terminus of Piccolino might interact with SVs. First, we ultrastructurally analyzed the distribution of SVs at photoreceptor ribbon synapses in Piccolino knock-out (KO) mice. We found a decrease in the density of ribbon-associated SVs in Piccolino KO photoreceptors, compared to wild-type (WT) synapses. In addition, we observed that in Piccolino KO photoreceptors, SVs were located significantly closer to SRs when compared to WT synapses. This indicates that SRs are unable to maintain the uniform distance between SVs and SRs in the absence of Piccolino. Both findings implicate Piccolino in organizing SVs at photoreceptor SRs. As a possible synaptic tethering mechanism, we identified an alpha-helical amphiphatic liquid packing sensor (ALPS) motif at the N-terminus of Piccolino. Protein-lipid binding studies confirm that purified fragments of Piccolino containing the ALPS motif readily bind to artificial, SV-like liposomes in a curvature- and charge-dependent manner. We thus propose that Piccolino performs tethering directly through protein-lipid binding. Mutation studies are underway to verify the importance of the Piccolino ALPS motif for lipid binding. 1Regus-Leidig H. et al., (2013) doi: 10.1371/journal.pone.0070373. 2Regus-Leidig H. et al., (2014) doi: 10.33.89/fncel.2014.00259. 3Müller T. et al., (2019) doi: 10.1523/JNEUROSCI.2038-18.2019.