title: Subunit contributions to phosphorylation-dependent modulation of bovine rod cyclic nucleotide-gated channels.
abstract: Cyclic nucleotide-gated (CNG) channels in rod photoreceptors transduce a decrease in cGMP into hyperpolarization during the light response. Insulin-like growth factor-1 (IGF-1) increases light responses by increasing the cGMP sensitivity of CNG channels, an event mediated by a protein tyrosine phosphatase. Native rod CNG channels are heteromultimers, composed of three CNGA1 subunits and one CNGB1 subunit. Previous studies on heterologously expressed rod CNG channels show that a specific tyrosine in the CNGA1 subunit (Y498) is required for modulation by protein tyrosine phosphatases, protein tyrosine kinases and IGF-1. Here we show that the CNGB1 subunit contains a specific tyrosine (Y1097) that is important for modulation of heteromeric channels by tyrosine phosphorylation. Direct biochemical measurements demonstrate 32P-labelling of CNGA1Y498 and CNGB1Y1097. Replacement of either Y498 of CNGA1 or Y1097 of CNGB1 with phenylalanine reduces modulation, and removal of both tyrosines eliminates modulation. Unlike CNGA1, CNGB1 does not exhibit activity dependence of modulation by tyrosine phosphorylation. Hence both CNGA1 and CNGB1 subunits contribute to phosphorylation-dependent modulation of rod CNG channels, but the phosphorylation states of the two subunits are regulated in different ways.
authors.affiliation: Deparment of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA. rhkramer@uclink4.berkeley.edu
authors.forename: Elena
authors.initials: E
authors.lastname: Molokanova
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Krajewski
authors.forename: Daulet
authors.initials: D
authors.lastname: Satpaev
authors.forename: Charles W
authors.initials: CW
authors.lastname: Luetje
authors.forename: Richard H
authors.initials: RH
authors.lastname: Kramer
mesh_terms: D000818:Animals; D002417:Cattle; D000242:Cyclic AMP / Q000502:physiology*; D006152:Cyclic GMP / Q000502:physiology*; D054815:Cyclic Nucleotide-Gated Cation Channels; D018076:DNA, Complementary / Q000096:biosynthesis / Q000235:genetics; D004594:Electrophysiology; D007334:Insulin-Like Growth Factor I / Q000502:physiology; D015640:Ion Channel Gating / Q000502:physiology*; D007473:Ion Channels / Q000502:physiology*; D016296:Mutagenesis; D009419:Nerve Tissue Proteins; D009865:Oocytes / Q000378:metabolism; D010766:Phosphorylation; D011506:Proteins / Q000502:physiology*; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014443:Tyrosine / Q000502:physiology; D014982:Xenopus laevis
chemical_list: C475741:CNGA1 protein, bovine; C034698:CNGB1 protein, Bos taurus; D054815:Cyclic Nucleotide-Gated Cation Channels; D018076:DNA, Complementary; D007473:Ion Channels; D009419:Nerve Tissue Proteins; D011506:Proteins; D014443:Tyrosine; D007334:Insulin-Like Growth Factor I; D000242:Cyclic AMP; D006152:Cyclic GMP