Structure of mammalian endolysosomal TRPML1 channel in nanodiscs

Abstract

Transient receptor potential mucolipin 1 (TRPML1) is an endo/lysosomal cation channel ubiquitously expressed in mammalian cells1,2 and its loss-of-function mutations are the direct cause of Type IV mucolipidosis (MLIV), an autosomal recessive lysosomal storage disease3-6. Here we present the single particle cryo-electron microscopy (cryo-EM) structure of the mouse TRPML1 channel embedded in nanodiscs. Combined with mutagenesis, the TRPML1 structure reveals that phosphatidylinositol bisphosphate (PIP2) binds to the N-terminus of the channel – distal from the pore – and the helix-turn-helix extension between S2 and S3 likely couples ligand binding to pore opening. The tightly packed selectivity filter contains multiple ion binding sites and the conserved acidic residues form the luminal Ca2+ blocking site that confers luminal pH and Ca2+ modulation on channel conductance. A luminal linker domain forms a fenestrated canopy atop the channel, providing multiple luminal ion passages to the pore and also creating a negative electrostatic trap – preferably for divalent cations at the luminal entrance. The structure also reveals two equally distributed S4-S5 linker conformations in the closed channel, providing structural implication for the S4-S5 linker-mediated PIP2 gating mechanism among TRPML channels7,8.

Human TRPML1 channel structures in open and closed conformations

“…Previous studies have shown that there is a PtdIns(3,5)P 2 -binding site in the positively charged pre-S1 region of TRPML1 15 , which is distant from the ML-SA1-binding site that we mapped in the membrane domain. A related Nature paper provides specific insights into TRPML1 in the lipid environment 42 .…”

Structure of the human TRPM4 ion channel in a lipid nanodisc

“…1C, D) reminiscent of many tetrameric voltage-gated cation channels, and all other TRP channels to date (7–13). hTRPM4 has additional membrane embedded fragments that surround the S1–S4 domain from the inner leaflet of the membrane (Fig.…”

Precisely Controlling Nanochannels of Graphene Oxide Membranes through Lignin‐Based Cation Decoration for Dehydration of Biofuels

“…[2] Grapheneo xide (GO) has been the most frequently employed derivativeo fg raphene for developing such membranes, owing to its abundant oxygenated groups, [3] which enable its dispersion in water and greatly improvet he possibilities for assembly of membrane nanostructures, including laminates and hybrids. [10] Nevertheless, the efficient rejection of ions through the cation-controlled GO membranes relied on aqueous solutionsc ontaining cations that are not often presenti na pplicationsf or processes such as solvent dehydration or gas separation. Strategies involving covalent bonding, [6] hydrogen bonding, [7] electrostatic attraction, [8] and chemicalr eduction [9] have been designed to enhance the structural stabilityo fG O membranes.…”

“…[10] Nevertheless, the efficient rejection of ions through the cation-controlled GO membranes relied on aqueous solutionsc ontaining cations that are not often presenti na pplicationsf or processes such as solvent dehydration or gas separation. The resulting cation-controlled GO membranes exhibited excellent ion-sieving properties to effect water desalination.…”