Identification and characterization of two distinct calmodulin-binding sites in the Trpl ion-channel protein of Drosophila melanogaster.
Two putative light-sensitive ion channels have been isolated from Drosophila, encoded by the transient-receptor-potential (trp) and transient-receptor-potential-like (trpl) genes. The cDNA encoding the Trpl protein was initially isolated on the basis that the expressed protein binds calmodulin. Using both fusion proteins and a synthetic peptide, we now show that two calmodulin-binding sites are present in the C-terminal domain of the Trpl protein, CBS-1 and CBS-2. CBS-1 binds calmodulin in a Ca2+-dependent fashion, requiring Ca2+ concentrations above 0.3-0.5 microM for calmodulin binding. In contrast, CBS-2 binds the Ca2+-free form of calmodulin, with dissociation occurring at Ca2+ concentrations between 5 and 25 microM. Phosphorylation of a serine residue within a peptide encompassing CBS-1 by cyclic AMP-dependent protein kinase (PKA) abolishes calmodulin binding, and phosphorylation of the adjacent serine by protein kinase C appears to modulate this phosphorylation by PKA. Interpretation of these findings provides a novel model for ion-channel gating and modulation in response to changing levels of intracellular Ca2+.
Warr
C G
CG
Department of Genetics, University of Melbourne, Parkville, Victoria, Australia.
Kelly
L E
LE
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000378:metabolism*; D007301:Insect Hormones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019476:Insect Proteins; D015640:Ion Channel Gating; D008969:Molecular Sequence Data; D010766:Phosphorylation; D050051:Transient Receptor Potential Channels
D015220:Calcium Channels; D002147:Calmodulin; D029721:Drosophila Proteins; D007301:Insect Hormones; D019476:Insect Proteins; D050051:Transient Receptor Potential Channels; C063169:trp protein, Drosophila; D002118:Calcium