There are at least two different principles of how ADP-ribose (ADPR) induces activation of TRPM2 channels. In human TRPM2, gating requires the C-terminal NUDT9H domain as ADPR-binding module, whereas in sea anemone, NUDT9H is dispensable and binding of ADPR occurs N-terminally. Zebrafish TRPM2 needs both, the N-terminal ADPR-binding pocket and NUDT9H. Our aim was to pinpoint the relative functional contributions of NUDT9H and the N-terminal ADPR-binding pocket in zebrafish TRPM2, to identify fundamental mechanisms of ADPR-directed gating. We show that the NUDT9H domains of human and zebrafish TRPM2 are interchangeable since chimeras generate ADPR-sensitive channels. A point mutation at a highly conserved position within NUDT9H induces loss-of-function in both vertebrate channels. The substrate specificity of zebrafish TRPM2 corresponds to that of sea anemone TRPM2, indicating gating by the proposed N-terminal ADPR-binding pocket. However, a point mutation in this region abolishes ADPR activation also in human TRPM2. These findings provide functional evidence for an uniform N-terminal ADPR-binding pocket in TRPM2 of zebrafish and sea anemone with modified function in human TRPM2. The structural importance of NUDT9H in vertebrate TRPM2 can be associated with a single amino acid residue which is not directly involved in the binding of ADPR.

In humans, the cation channel TRPM2 (HsTRPM2) has been intensively studied because it is involved in oxidative stress mediated apoptosis and also contributes to temperature regulation. The gating mechanism of TRPM2 is quite complex where a C-terminally localized enzyme domain plays a crucial role. The analysis of orthologues of TRPM2, in particular from the distantly related marine invertebrate Nematostella vectensis (NvTRPM2) revealed that during evolution the functional role of the endogenous enzyme domain of TRPM2 has undergone fundamental changes. In this study we investigate whether these evolutionary differences also apply to the physiological functions of TRPM2. For this purpose, we generated a TRPM2 loss-of-function mutation in Nematostella and compared the phenotypes of wild-type and mutant animals after exposure to either oxidative stress or high temperature. Our results show that under standard culture conditions mutant animals are indistinguishable from wild-type animals in terms of morphology, and development. However, exposure of both experimental groups to different stressors revealed that TRPM2 sensitizes to oxidative stress but attenuates high temperature injury in Nematostella. Therefore, NvTRPM2 plays opposite roles in the cellular response to these two different stressors. These findings reveal a similar physiological spectrum of activity of TRPM2 in humans and Nematostella and open up the possibility to establish Nematostella as a model organism for the physiological function of TRPM2.