RT Journal Article
SR Electronic
T1 Activity-Dependent Modulation of Rod Photoreceptor Cyclic Nucleotide-Gated Channels Mediated by Phosphorylation of a Specific Tyrosine Residue
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 4786
OP 4795
DO 10.1523/JNEUROSCI.19-12-04786.1999
VO 19
IS 12
A1 Elena Molokanova
A1 Floyd Maddox
A1 Charles W. Luetje
A1 Richard H. Kramer
YR 1999
UL http://www.jneurosci.org/content/19/12/4786.abstract
AB Cyclic nucleotide-gated (CNG) channels are crucial for phototransduction in vertebrate rod photoreceptors. The cGMP sensitivity of these channels is modulated by diffusible intracellular messengers, including Ca2+/calmodulin, contributing to negative feedback during sensory adaptation. Membrane-associated protein tyrosine kinases and phosphatases also modulate rod CNG channels, but whether this results from direct changes in the phosphorylation state of the channel protein has been unclear. Here, we show that bovine rod CNG channel α-subunits (bRET) contain a tyrosine phosphorylation site crucial for modulation. bRET channels expressed in Xenopus oocytes exhibit modulation, whereas rat olfactory CNG channels (rOLF) do not. Chimeric channels reveal that differences in the C terminus, containing the cyclic nucleotide-binding domain, account for this difference. One specific tyrosine in bRET (Y498) appears to be crucial; replacement of this tyrosine in bRET curtails modulation, whereas installation into rOLF confers modulability. As the channel becomes dephosphorylated, there is an increase in the rate of spontaneous openings in the absence of ligand, indicating that changes in the phosphorylation state affect the allosteric gating equilibrium. Moreover, we find that dephosphorylation, which favors channel opening, requires open channels, whereas phosphorylation, which promotes channel closing, requires closed channels. Hence, modulation by changes in tyrosine phosphorylation is activity-dependent and may constitute a positive feedback mechanism, contrasting with negative feedback systems underlying adaptation.