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+.[1]References
- Identification and characterization of two distinct calmodulin-binding sites in the Trpl ion-channel protein of Drosophila melanogaster. Warr, C.G., Kelly, L.E. Biochem. J. (1996) [Pubmed]
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