1.A.5.3.3
Mucolipin-2 (TRPML2) non-selective plasma membrane cation channel (Ca²⁺ permeable). Shows inward rectification like TRPML1 and TRPML3 (Lev et al., 2010). Induces cell degeneration. Causes embryonic lethality, pigmentation defects and deafness, and regulates the acidification of early endosomes (Noben-Trauth, 2011). Found in the plasma membrane and early- and late-endosomes as well as lysosomes.  Activated by a transient reduction of extracellular sodium followed by sodium replenishment, by small chemicals related to sulfonamides, and by PI(3,5)P2, a rare phosphoinositide that naturally accumulates in the membranes of endosomes and lysosomes, and thus could act as a physiologically relevant agonist (García-Añoveros and Wiwatpanit 2014).  TRPML2 can form heteromultimers with TRPML1 and TRPML3; in B-lymphocytes, TRPML2 and TRPML1 may play redundant roles.  TRPML2 may play a role in immune cell development and inflammatory responses (Cuajungco et al. 2015). The TRPML family hallmark is a large extracytosolic/lumenal domain (ELD) between TMSs S1 and S2. Viet et al. 2019 presented crystal structures of the tetrameric human TRPML2 ELD. The structures reveal structural responses to the conditions the TRPML2 ELD encounters as the channel traffics through the endolysosomal system.