Abstract
An important mechanism by which vertebrate olfactory sensory neurons rapidly adapt to odorants is feedback modulation of the Ca2+-permeable cyclic nucleotide–gated (CNG) transduction channels. Extensive heterologous studies of homomeric CNGA2 channels have led to a molecular model of channel modulation based on the binding of calcium-calmodulin to a site on the cytoplasmic amino terminus of CNGA2. Native rat olfactory CNG channels, however, are heteromeric complexes of three homologous but distinct subunits. Notably, in heteromeric channels, we found no role for CNGA2 in feedback modulation. Instead, an IQ-type calmodulin-binding site on CNGB1b and a similar but previously unidentified site on CNGA4 are necessary and sufficient. These sites seem to confer binding of Ca2+-free calmodulin (apocalmodulin), which is then poised to trigger inhibition of native channels in the presence of Ca2+.
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Acknowledgements
We thank J. Reisert and V. Bhandawat for many discussions; J. Kehoe, B. Barbour, N. Pardigon, J. Lynch, S. Hattar, R. Kuruvilla and P. Bauer for comments; P. Ascher for critically reading the manuscript and V. Kefelov for suggesting the experiment for Figure 2c. J.B. dedicates this paper to Norman Davidson. This work was supported by the Deutsche Forschungsgemeinschaft under grant SPP 1025 (S.F.) and by the Howard Hughes Medical Institute (J.B. & K.-W.Y.).
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Bradley, J., Bönigk, W., Yau, KW. et al. Calmodulin permanently associates with rat olfactory CNG channels under native conditions. Nat Neurosci 7, 705–710 (2004). https://doi.org/10.1038/nn1266
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DOI: https://doi.org/10.1038/nn1266
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