title: Mechanism of calcium/calmodulin inhibition of rod cyclic nucleotide-gated channels.
abstract: Rod cyclic nucleotide-gated (CNG) channels are heterotetramers comprised of both CNGA1 and CNGB1 subunits. Calcium/calmodulin (Ca(2+)/CaM) binds to a site in the N-terminal region of CNGB1 subunits and inhibits the opening conformational change in CNGA1/CNGB1 channels. Here, we show that polypeptides derived from an N-terminal region of CNGB1 form a specific interaction with polypeptides derived from a C-terminal region of CNGA1 that is distal to the cyclic nucleotide-binding domain. Deletion of the Ca(2+)/CaM-binding site from the N-terminal region of CNGB1 eliminated both Ca(2+)/CaM modulation of the channel and the intersubunit interaction. Furthermore, the interaction was disrupted by the presence of Ca(2+)/CaM. These results suggest that Ca(2+)/CaM-dependent inhibition of rod channels is caused by the direct binding of Ca(2+)/CaM to a site in the N-terminal region in CNGB1, which disrupts the interaction between this region and a distal C-terminal region of CNGA1. The mechanism underlying Ca(2+)/CaM modulation of rod channels is distinct from that in olfactory (CNGA2) CNG channels.
authors.affiliation: Department of Physiology and Biophysics, Howard Hughes Medical Institute, University of Washington Medical School, Box 357370, Seattle, WA 98195, USA.
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Trudeau
authors.forename: William N
authors.initials: WN
authors.lastname: Zagotta
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology*; D002417:Cattle; D003001:Cloning, Molecular; D054815:Cyclic Nucleotide-Gated Cation Channels; D005260:Female; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000502:physiology*; D008958:Models, Molecular; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology*; D014982:Xenopus laevis
chemical_list: D002147:Calmodulin; D054815:Cyclic Nucleotide-Gated Cation Channels; D007473:Ion Channels; D011994:Recombinant Proteins; D002118:Calcium