Adapter protein that regulates and/or fission of intracellular vesicles such as lysosomes (By similarity). Might regulate trafficking of effectors involved in exocytosis (By similarity). In cytotoxic T-cells and natural killer (NK) cells, has role in the regulation of size, number and exocytosis of lytic granules (By similarity). In macrophages and dendritic cells, regulates phagosome maturation by controlling the conversion of early phagosomal compartments into late phagosomes (PubMed:27881733). In macrophages and dendritic cells, specifically involved in TLR3- and TLR4-induced production of pro-inflammatory cytokines by regulating the endosomal TLR3- TICAM1/TRIF and TLR4- TICAM1/TRIF signaling pathways (PubMed:27881733). Interacts with CENPJ, LIP8 and ZNF521. Additional isoforms seem to exist. Expressed in the heart, lung, liver, spleen, brain and in different immune cell types (purified B and T lymphocytes, bone marrow-derived macrophages and dendritic cells). Defects in Lyst are the cause of beige (bg), an autosomal recessive disorder characterized by hypopigmentation, bleeding, immune cell dysfunction, abnormal intracellular transport to and from the lysosome, and giant inclusion bodies in a variety of cell types.