Nonselective cation channel probably playing a role in the regulation of membrane trafficking events and of metal homeostasis (PubMed:29019981). Proposed to play a major role in Ca(2+) release from late endosome and lysosome vesicles to the cytoplasm, which is important for many lysosome-dependent cellular events, including the fusion and trafficking of these organelles, exocytosis and autophagy. Required for efficient uptake of large particles in macrophages in which Ca(2+) release from the lysosomes triggers lysosomal exocytosis. May also play a role in phagosome-lysosome fusion (PubMed:23993788, PubMed:27623384). Involved in lactosylceramide trafficking indicative for a role in the regulation of late endocytic membrane fusion/fission events. By mediating lysosomal Ca(2+) release is involved in regulation of mTORC1 signaling and in mTOR/TFEB-dependent lysosomal adaptation to environmental cues such as nutrient levels (PubMed:25733853). Seems to act as lysosomal active oxygen species (ROS) sensor involved in ROS-induced TFEB activation and autophagy (By similarity). Functions as a Fe(2+) permeable channel in late endosomes and lysosomes. Proposed to play a role in zinc homeostasis probably implicating its association with TMEM163 (By similarity). In adaptive immunity, TRPML2 and TRPML1 may play redundant roles in the function of the specialized lysosomes of B cells (PubMed:17050035). May contribute to cellular lipase activity within the late endosomal pathway or at the cell surface which may be involved in processes of membrane reshaping and vesiculation, especially the growth of tubular structures. However, it is not known, whether it conveys the enzymatic activity directly, or merely facilitates the activity of an associated phospholipase. Channel activity is controlled by multiple regulatory mechanisms in different subcellular compartments (By similarity). Channel function is transiently modulated by changes in Ca(2+), and inhibited by a reduction of pH; pH changes modify the aggregation state of unitary channels; a negative cooperativity between extracellular/lumenal Ca(2+) and H(+) is suggested (PubMed:29019981). Regulated by phosphoinositides in a compartment-specific manner: in lysosomes activated by PtdIns(3,5)P2 (Phosphatidylinositol 3,5-bisphosphate) and at the plasma membrane inhibited by PtdIns(4,5)P2 (Phosphatidylinositol 4,5-bisphosphate) (PubMed:29019981). Homotetramer (PubMed:29019981). Homooligomer. Can heterooligomerize with MCOLN2 or MCOLN3; heteromeric assemblies have different channel properties as compared to the respective homooligomers and may be tissue-specific. Interacts with PDCD6. Interacts with TMEM163. Interacts with LAPTM4B (By similarity). Delivery from the trans-Golgi to lysosomes seems to occur mainly in a direct intracellular manner without intermediate delivery to the plasma membrane (By similarity). Under normal conditions, restricted to intracellular compartments so that only a very minor proportion is present at the cell membrane (PubMed:29019981). Widely expressed, with the highest expression in brain, liver and kidney. Up-regulated by nutrient starvation. The most N-terminal extracellular/lumenal domain (referred to as I-II linker or polycystin-mucolipin domain) contributes to a structure with a four-fold rotational symmetry in a tetrameric assembly; the structure contains a central highly electronegative pore with a 14 A diameter. The pore is critical for Ca(2+) and pH regulation. The protruding structure formed by the I-II linkers may contain all the interaction sites with lipids and proteins in the endolysosomal lumen. Palmitoylated; involved in association with membranes. Phosphorylation by PKA inhibits channel activity. Dephosphorylation increases activity. Proteolytically cleaved probably involving multiple lysosomal proteases including cathepsin B; inhibits lysosomal channel activity. Belongs to the transient receptor (TC 1.A.4) family. Polycystin subfamily. MCOLN1 sub-subfamily.