title: TRPC channel interactions with calmodulin and IP3 receptors.
abstract: Consistent with the conformational coupling mechanism, which suggests that store-operated channels are activated via physical interactions with intracellular calcium release channels, previous studies have demonstrated a functional coupling and a physical interaction between the transient receptor potential canonical type 3 (TRPC3) and inositol 1,4,5-trisphosphate receptor (IP3R). The IP3R-TRPC binding domains were determined using in vitro binding assays. This work aimed to study the effect of IP3R-TRPC interaction on TRPC function. Pull-down experiments were used to study the binding of TRPC to IP3R and to calmodulin. Patch clamp recordings in whole-cell and inside-out configurations were used to examine the effect of a TRPC-binding IP3R fragment, Ca2+ and calmodulin on TRPC activity. We found that IP3R and calmodulin compete for a common binding site at the TRPC C-terminus. TRPC channels are activated either by a peptide representing the TRPC-binding domain of IP3R or by inactivation of calmodulin from the excised membrane patches. TRPC3 activity is inhibited by Ca2+ and calmodulin. Therefore, we have identified a critical IP3R-TRPC interaction that is involved in the activation of TRPC-formed channels. We propose that IP3Rs activate TRPC channels by displacing inhibitory calmodulin from a common calmodulin-IP3R binding site located at the C-terminus of TRPC.
authors.affiliation: Center for Molecular Neurobiology and Department of Neuroscience, The Ohio State University, 168 Rightmire Hall, 1060 Carmack Road, Columbus, Ohio 43210, USA.
authors.forename: Michael X
authors.initials: MX
authors.lastname: Zhu
authors.forename: Jisen
authors.initials: J
authors.lastname: Tang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002147:Calmodulin / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism; D011485:Protein Binding; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D050052:TRPC Cation Channels
chemical_list: D015220:Calcium Channels; D002147:Calmodulin; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007473:Ion Channels; D010446:Peptide Fragments; D018160:Receptors, Cytoplasmic and Nuclear; D050052:TRPC Cation Channels; C104603:TRPC3 cation channel; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium