Structural basis of dual Ca2+/pH regulation of the endolysosomal TRPML1 channel

Abstract

Organellar ion channels are essential for cell physiology. Their activities are often regulated by Ca2+ and H+, which are concentrated in many organelles. Here we report a novel structural element critical for Ca2+/pH dual regulation of TRPML1, a Ca2+ release channel crucial for endolysosomal functions. TRPML1 mutations cause mucolipidosis type IV (MLIV), a severe lysosomal storage disorder characterized by neurodegeneration, mental retardation and blindness. We obtained high-resolution crystal structures of a 213-amino acid luminal domain of human TRPML1 that harbors three missense MLIV-causing mutations. This domain forms a tetramer with a highly electronegative central pore formed by a novel luminal pore-loop. Cysteine crosslinking and cryo-EM confirm this structure in the full-length channel. Structure-function studies demonstrate that Ca2+ and H+ interact with the luminal pore to exert physiologically important regulation. The MLIV-causing mutations disrupt the luminal domain structure and cause TRPML1 mislocalization. Our study provides a structural underpinning for TRPML1's regulation, assembly and pathogenesis.

Structural basis of TRPV5 channel inhibition by econazole revealed by cryo-EM

“…Our cryo-EM structure of the econazole-bound full-length TRPV5 channel exhibits a domain-swapped architecture, which is a hallmark of all currently determined TRP channels at atomic resolution 11–18 and was recently confirmed to be present in TRPV6 (refs. 19,20 ).…”

“…All recently determined cryo-EM structures of TRP channels have revealed a domain-swapped architecture that is shared by many voltage-gated ion channels 11–18 . As expected, the full-length TRPV5 structure is similar to other TRPV subfamily structures 11–13 (Fig.…”

“…11–13 ). Subsequently, the structures of other TRP channels have been determined using cryo-EM, revealing structural diversity among family members 14–18 . The X-ray structures of modified and truncated TRPV6 constructs have also been solved 19,20 , and these structures indicated a mechanism of Ca 2+ permeation but did not provide information regarding ligand binding, modulation and channel gating.…”

Structure of mammalian endolysosomal TRPML1 channel in nanodiscs

“…1a). The 200-residue, luminal-facing linker domain between S1 and S2 can self-assemble into a tetramer and its crystal structure 22 fits readily into our EM-density map, facilitating our model building. Asn230 of the luminal linker domain is glycosylated with visible density for the covalently linked N-acetylglucosamine moiety of the sugar (Fig.…”

“…The enrichment of Ca 2+ ions can effectively limit the access of monovalent cations to the filter and, thereby, reduce the permeation of monovalent ions. Indeed, it has been shown that neutralizing the acidic residues on the luminal pore loop weakens the Ca 2+ blockage 22 .…”