Activation of Trp3 by inositol 1,4,5-trisphosphate receptors through displacement of inhibitory calmodulin from a common binding domain.
Mammalian homologues of Drosophila Trp form plasma membrane channels that mediate Ca(2+) influx in response to activation of phospholipase C and internal Ca(2+) store depletion. Previous studies showed that human Trp3 is activated by inositol 1,4,5-trisphosphate (IP(3)) receptors (IP(3)Rs) and identified interacting domains, one on Trp and two on IP(3)R. We now find that Trp3 binds Ca(2+)-calmodulin (Ca(2+)/CaM) at a site that overlaps with the IP(3)R binding domain. Using patch-clamp recordings from inside-out patches, we further show that Trp3 has a high intrinsic activity that is suppressed by Ca(2+)/CaM under resting conditions, and that Trp3 is activated by the following: a Trp-binding peptide from IP(3)R that displaces CaM from Trp3, a myosin light chain kinase Ca(2+)/CaM binding peptide that prevents CaM from binding to Trp3, and calmidazolium, an inactivator of Ca(2+)/CaM. We conclude that inhibition of the inhibitory action of CaM is a key step of Trp3 channel activation by IP(3)Rs.
Neurobiotechnology Center and Departments of Neuroscience and Molecular and Cellular Biochemistry, Ohio State University, Columbus, OH 43210, USA.
Z
Z
Zhang
J
J
Tang
S
S
Tikunova
J D
JD
Johnson
Z
Z
Chen
N
N
Qin
A
A
Dietrich
E
E
Stefani
L
L
Birnbaumer
M X
MX
Zhu
D000595:Amino Acid Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002413:Cations, Divalent; D002460:Cell Line; D006801:Humans; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008969:Molecular Sequence Data; D010455:Peptides / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D050052:TRPC Cation Channels
D015220:Calcium Channels; D002147:Calmodulin; D002413:Cations, Divalent; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D010455:Peptides; D018160:Receptors, Cytoplasmic and Nuclear; D050052:TRPC Cation Channels; C104603:TRPC3 cation channel; D002118:Calcium