Molecular Mechanism of TRPM2 Gating

Abstract

Transient receptor potential (TRP) melastatin 2 (TRPM2) is a ubiquitously expressed cation channel associated with chronic inflammatory and neurodegenerative diseases. Different from other members of the TRP superfamily, TRPM2 has a C-terminal cytosolic NUDT9-homology (NUDT9H) domain, which is responsible for binding adenosine diphosphate ribose (ADPR), and both ADPR and intracellular Ca2+are required for TRPM2 activation. Here we present cryo-electron microscopy (cryo-EM) structures of human TRPM2, alone, in complex with ADPR, and in complex with ADPR and Ca2+, representing in closed, primed, and open states respectively. Instead of being flexibly linked at the C-terminal end as previously assumed, NUDT9H folds back onto the N-terminal TRPM homology region (MHR) of TRPM2 and forms both intra- and inter-subunit interactions in the tetrameric channel. The NUDT9H domain undergoes conformational changes upon ADPR engagement, resulting in rotation of the MHR and disengagement of the inter-subunit interaction. We found that Ca2+binding directly engages the conserved TRP helix of TRPM2, which acts as a lever to cause a conformational change at the connected lower gating pore to open the channel. Because the TRP helix is coupled to the MHR arm, the Ca2+-induced conformational change is only allowed when the inter-subunit interaction between NUDT9H and MHR is abolished by ADPR binding, a process we name priming, which explains the molecular mechanism of concerted TRPM2 channel gating by ADPR and Ca2+. Structural analysis further suggests that TRP helix-induced gating may be general for many TRP channels.