A conserved mechanism couples cytosolic domain movements to pore gating in the TRPM2 channel

Transient Receptor Potential Melastatin 2 (TRPM2) cation channels contribute to immunocyte activation, insulin secretion, and central thermoregulation. TRPM2 opens upon binding cytosolic Ca²⁺ and ADP ribose (ADPR). We present here the 2.5 Å cryo-electronmicroscopy structure of TRPM2 from <i>Nematostella vectensis</i> (nvTRPM2) in a lipid nanodisc, complexed with Ca²⁺ and ADPR-2'-phosphate. Comparison with nvTRPM2 without nucleotide reveals that nucleotide binding-induced movements in the protein's three "core" layers deconvolve into a set of rigid-body rotations conserved from cnidarians to man. By covalently crosslinking engineered cysteine pairs we systematically trap the cytosolic layers in specific conformations and study effects on gate opening/closure. The data show that nucleotide binding in Layer 3 disrupts inhibitory intersubunit interactions, allowing rotation of Layer 2 which in turn expands the gate located in Layer 1. Channels trapped in that "activated" state are no longer nucleotide dependent, but are opened by binding of Ca²⁺ alone.