Non-canonical pore architecture underlies constitutive gating of human retinal TRPM1.

Transient receptor potential melastatin 1 (TRPM1), a Ca²⁺-permeable nonselective cation channel essential for retinal ON bipolar cell signaling and night vision, and implicated in congenital night blindness, has remained structurally and functionally poorly characterized. Here we report the cryo-electron microscopy structure of human TRPM1, revealing that although it assembles as a tetramer, it adopts an unexpected clockwise domain-swapped pore module with rotational geometry inverse to that observed in previously characterized 6-TM tetrameric channels. This inverted topology is accompanied by extensive remodeling of the S5-P-S6 module, dilation of the selectivity filter, expansion of the central cavity, and splaying of S6 to form a wide intracellular gate. Our single-channel recordings reveal constitutive activity consistent with the conductive state captured. Together, these findings uncover a 6-TM fold in the tetrameric channel and provide a framework for understanding TRPM1 gating, disease-associated dysfunction, and associated pharmacology.