Component of the biogenesis of lysosome-related organelles complex-1 (BLOC-1) involved in pigment granule biogenesis and membrane trafficking in synapses (PubMed:20015953, PubMed:28317021). In response to high synaptic activity at neuromuscular junctions, plays a key role in promoting efficient synaptic vesicle recycling and re-formation through early endosomes (PubMed:28317021). Component of the biogenesis of lysosome-related organelles complex-1 (BLOC-1) composed of Blos1, Blos2, Blos3, Blos4, Dysb, Muted, Pldn and Snapin. Interacts with Blos1, Blos4 and Dysb. At the neuromuscular junctions, present at both pre- and postsynaptic compartments where it associates with cytoskeletal neuronal microtubule structures and muscle Z-lines. Expressed throughout development from embryo to adult stages (at protein level) (PubMed:28317021). In larvae, expressed at the neuromuscular junction both pre- and postsynaptically (at protein level) (PubMed:28317021). Viable and fertile (PubMed:28317021). In the neuromuscular junctions, results in abnormal tubular endosomal compartments and a reduction in early endosomes which leads to a decrease recycling and recovery of the synaptic vesicle pool and results in failure to sustain neurotransmitter release during high-frequency stimulation (PubMed:28317021). Does not affect synaptic morphology or basal function (PubMed:28317021). Belongs to the BLOC1S6 family.