The transient receptor potential, TRP4, cation channel is a novel member of the family of calmodulin binding proteins

The mammalian gene products, transient receptor potential (trp)1 to trp7, are related to the Drosophila TRP and TRP-like ion channels, and are candidate proteins underlying agonist-activated Ca2+-permeable ion channels. Recently, the TRP4 protein has been shown to be part of native store-operated Ca2+ permeable channels. These channels, most likely, are composed of other proteins in addition to TRP4. In the present paper we report the direct interaction of TRP4 and calmodulin (CaM) by: (1) retention of in vitro translated TRP4 and of TRP4 protein solubilized from bovine adrenal cortex by CaM-Sepharose in the presence of Ca2+, and (2) TRP4-glutathione S-transferase pull-down experiments. Two domains of TRP4 amino acid residues 688-759 and 786-848, were identified as being able to interact with CaM. The binding of CaM to both domains occurred only in the presence of Ca2+ concentrations above 10 muM, with half maximal binding occurring at 16.6 muM (domain 1) and 27.9 muM Ca2+ (domain 2). Synthetic peptides, encompassing the two putative CaM binding sites within these domains and covering amino acid residues 694-728 and 829-853, interacted directly with dansyl-CaM with apparent K-d values of 94-189 nM. These results indicate that TRP4/Ca2+-CaM are parts of a signalling complex involved in agonist-induced Ca2+ entry.