Activity of the yeast vacuolar TRP channel TRPY1 is inhibited by Ca-calmodulin binding.

Transient receptor potential (TRP) cation channels, which are conserved across mammals, flies, fish, sea squirts, worms, and fungi, essentially contribute to cellular Ca signaling. The activity of the unique TRP channel in yeast, TRP yeast channel 1 (TRPY1), relies on the vacuolar and cytoplasmic Ca concentration. However, the mechanism(s) of Ca-dependent regulation of TRPY1 and possible contribution(s) of Ca-binding proteins are yet not well understood. Our results demonstrate a Ca-dependent binding of yeast calmodulin (CaM) to TRPY1. TRPY1 activity was increased in the cmd1-6 yeast strain, carrying a non-Ca-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 Ca influx and Ca release were increased by the CaM antagonist ophiobolin A. We found that coexpression of mammalian CaM impeded the activity of TRPY1 by reinforcing effects of endogenous CaM. Finally, inhibition of TRPY1 by Ca-CaM required the cytoplasmic amino acid stretch E-Y. In summary, our results show that TRPY1 is under inhibitory control of Ca-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 Ca-sensing subunit, and contribute to a better understanding of the modulatory mechanisms of Ca-CaM.