Activity of the yeast vacuolar TRP channel TRPY1 is inhibited by Ca2+-calmodulin binding

Transient receptor potential (TRP) cation channels, which are conserved across mammals, flies, fish, sea squirts, worms, and fungi, essentially contribute to cellular Ca2+ signaling. The activity of the unique TRP channel in yeast, TRP yeast channel 1 (TRPY1), relies on the vacuolar and cytoplasmic Ca2+ concentration. However, the mechanism(s) of Ca2+- dependent regulation of TRPY1 and possible contribution(s) of Ca2+-binding proteins are yet not well understood. Our results demonstrate a Ca2+-dependent binding of yeast calmodulin (CaM) to TRPY1. TRPY1 activity was increased in the cmd1-6 yeast strain, carrying a non-Ca2+-binding CaM mutant, compared with the parent strain expressing wt CaM (Cmd1). Expression of Cmd1 in cmd1-6 yeast rescued the wt phenotype. In addition, in human embryonic kidney 293 cells, hypertonic shock-induced TRPY1-dependent Ca2+ influx and Ca2+ release were increased by the CaM antagonist ophio-bolin A. We found that coexpression of mammalian CaM impeded the activity of TRPY1 by reinforcing effects of endogenous CaM. Finally, inhibition of TRPY1 by Ca2+-CaM required the cytoplasmic amino acid stretch E33-Y92. In summary, our results show that TRPY1 is under inhibitory control of Ca2+-CaM and that mammalian CaM can replace yeast CaM for this inhibition. These findings add TRPY1 to the innumerable cellular proteins, which include a variety of ion channels, that use CaM as a constitutive or dissociable Ca2+-sensing subunit, and contribute to a better under-standing of the modulatory mechanisms of Ca2+-CaM.