A histidine residue associated with the gate of the cyclic nucleotide-activated channels in rod photoreceptors.
Ion channels directly activated by the binding of cGMP mediate the electrical response to light in rod photoreceptors. Here, we identify a region of the channel associated with the activation gate using potentiation by intracellular Ni2+. Low concentrations of Ni2+ caused a dramatic increase in the response of rod channels expressed in Xenopus oocytes to both cGMP and cAMP. Whereas saturating cAMP normally activated less than 1% of the channels, Ni2+ increased the cAMP potency nearly 50-fold. Ni2+ did not produce potentiation in the related channel from the olfactory epithelium. We localized the Ni(2+)-binding site to a histidine residue in the putative intracellular mouth of the rod channel (H420). We propose a mechanism for potentiation in which Ni2+ binds to H420 primarily when the channel is open, stabilizing the open conformation. These experiments suggest that H420 is associated with the activation gate.
Gordon
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SE
Department of Physiology and Biophysics, Howard Hughes Medical Institute, University of Washington School of Medicine, Seattle 98195.
Zagotta
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D000818:Animals; D001665:Binding Sites; D002417:Cattle; D000242:Cyclic AMP / Q000494:pharmacology*; D006152:Cyclic GMP / Q000494:pharmacology*; D004357:Drug Synergism; D004553:Electric Conductivity; D006639:Histidine / Q000378:metabolism*; D015640:Ion Channel Gating; D007473:Ion Channels / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D009532:Nickel / Q000378:metabolism / Q000494:pharmacology; D010786:Photoreceptor Cells / Q000502:physiology*; D011487:Protein Conformation; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology
D007473:Ion Channels; D006639:Histidine; D009532:Nickel; D000242:Cyclic AMP; D006152:Cyclic GMP