The essential inter-domain interaction between NUDT9H and channel domain of human TRPM2 is also accomplished in trans

Channel function of human transient receptor potential melastatin type 2 (hsTRPM2) essentially depends on its C-terminal domain NUDT9H, which is homologous to the human Nudix hydrolase NUDT9. This cytosolic enzyme specifically binds and cleaves adenosine 5'-diphosphate ribose (ADPR), which in turn represents the principal agonist of TRPM2. For hsTRPM2 the experimental data strongly suggest, that binding of ADPR to NUDT9H as well as to a separate N-terminal binding pocket induces channel gating. Recent cryogenic electron microscopy (cryo-EM) analyses have provided the first concrete clues as to how NUDT9H interacts with the channel domain. In the present study we take an alternative approach by testing co-expression of NUDT9H together with a C-terminally truncated non-functional variant of hsTRPM2. Our data obtained from co-immunoprecipitation and proximity ligation assays reveal that NUDT9H and channel domain also specifically interact when co-expressed as independent proteins. Most importantly, calcium imaging as well as whole-cell patch-clamp recordings demonstrate that this in-trans interaction restores channel function, after stimulation either with intracellular ADPR or with extracellular hydrogen peroxide. Moreover, point mutation N1326D within the NUDT9H domain previously shown to be essential for TRPM2 function significantly reduces co-immunoprecipitation of NUDT9H as well as ADPR-dependent channel activity. These findings open up new possibilities to identify the molecular determinants of this crucial inter-domain interaction.