Transient Receptor Potential Melastatin 2 (TRPM2) cation channels contribute to immunocyte
activation, insulin secretion, and central thermoregulation. TRPM2 opens upon binding
cytosolic Ca 2+ and ADP ribose (ADPR). We present here the 2.5 Å cryo-electronmicroscopy
structure of TRPM2 from Nematostella vectensis (nvTRPM2) in a lipid nanodisc, complexed
with Ca 2+ 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 Ca 2+ alone.