Mutations in the TRP Domain Differentially affect the Function of TRPM8

Sensing potential harmful stimuli is crucial for the survival of the organisms. The detection of these stimuli relies on specialized proteins that localize on the surface of certain sensory cells. The Transient Receptor Potential ion channels are involved in sensing some of those stimuli such as temperature, pH and different chemical compounds. Upon activation, they evoke ionic currents that trigger action potentials in primary sensory neurons.An important unsolved question regarding TRP channel's function, is how the energy of the activating stimuli is coupled to channel opening. Several lines of evidence have pointed to the cytosolic C-terminus of these channels, known as the TRP domain, as a pivotal coupling region.To further understand the role of this domain in channel function, we have designed a set of chimeras in the cold menthol receptor (TRPM8) that incorporate the corresponding region of the heat-activated TRPV1 channel. We focused in the small region between the last transmembrane segment (S6) and the TRP Box. Our data indicate that this small region is essential for the function of TRPM8 and TRPV1. within this region, we have found a mutation that turns TRPM8 into constitutively active (Y981E). Strikingly, this constitutive activity could become regulated upon the addition of another mutation within the same region (V986I). The resulting channel shows the same current amplitude as the wild type, but the response to voltage is faster. In addition mutations in the same region hamper TRPM8 function D991K. Based on the available TRPM8 structural model we interpret the effect of these mutations on the channel function and we propose a possible mechanism for the gating process of TRPM8.