MCOLN1
Domain
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.
Function
Nonselective cation channel probably playing a role in the regulation of membrane trafficking events and of metal homeostasis (PubMed:11013137, PubMed:12459486, PubMed:14749347, PubMed:15336987, PubMed:18794901, PubMed:25720963, PubMed:27623384, PubMed:29019983). Acts as a Ca(2+)-permeable cation channel with inwardly rectifying activity (PubMed:25720963, PubMed:29019983). 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 (PubMed:11013137, PubMed:12459486, PubMed:14749347, PubMed:15336987, PubMed:25720963, PubMed:27623384, PubMed:29019983). 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 (By similarity). Involved in lactosylceramide trafficking indicative for a role in the regulation of late endocytic membrane fusion/fission events (PubMed:16978393). 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:25720963, PubMed:25733853, PubMed:27787197). Seems to act as lysosomal active oxygen species (ROS) sensor involved in ROS-induced TFEB activation and autophagy (PubMed:27357649). Also functions as a Fe(2+) permeable channel in late endosomes and lysosomes (PubMed:18794901). Also permeable to Mg(2+), Na(+). K(+) and Cs(+) (By similarity). Proposed to play a role in zinc homeostasis probably implicating its association with TMEM163 (PubMed:25130899) In adaptive immunity, TRPML2 and TRPML1 may play redundant roles in the function of the specialized lysosomes of B cells (By similarity).
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.
Involvement in disease
Mucolipidosis 4
ML4
An autosomal recessive lysosomal storage disorder characterized by severe psychomotor retardation and ophthalmologic abnormalities, including corneal opacity, retinal degeneration and strabismus. Storage bodies of lipids and water-soluble substances are seen by electron microscopy in almost every cell type of the patients. Most patients are unable to speak or walk independently and reach a maximal developmental level of 1-2 years. All patients have constitutive achlorhydia associated with a secondary elevation of serum gastrin levels.
None
The disease is caused by variants affecting the gene represented in this entry.
Corneal dystrophy, Lisch epithelial
LECD
An autosomal dominant corneal dystrophy characterized by gray, band-shaped and feathery opacities in the cornea, that sometimes appear in whorled patterns. The opaque bands consist of clear, densely crowded, intra-epithelial blisters. Vision may be impaired if the bands involve the central cornea.
None
The disease is caused by variants affecting the gene represented in this entry.
Post-translational modifications
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 (PubMed:16257972).
Sequence Similarities
Belongs to the transient receptor (TC 1.A.4) family. Polycystin subfamily. MCOLN1 sub-subfamily.
Tissue Specificity
Widely expressed in adult and fetal tissues.
Cellular localization
- Late endosome membrane
- Multi-pass membrane protein
- Lysosome membrane
- Multi-pass membrane protein
- Cytoplasmic vesicle membrane
- Multi-pass membrane protein
- Cell projection
- Phagocytic cup
- Cytoplasmic vesicle
- Phagosome membrane
- Multi-pass membrane protein
- Cell membrane
- Multi-pass membrane protein
- Delivery from the trans-Golgi to lysosomes seems to occur mainly in a direct intracellular manner without intermediate delivery to the plasma membrane (PubMed:16497227). Under normal conditions, restricted to intracellular compartments so that only a very minor proportion is present at the cell membrane (PubMed:12459486, PubMed:18794901, PubMed:28112729, PubMed:29019983).
Alternative names
ML4, TRPML1, MSTP080, MCOLN1, Mucolipin-1, ML1, MG-2, Mucolipidin, Transient receptor potential channel mucolipin 1