title: An Ankyrin-G N-terminal Gate and Protein Kinase CK2 Dually Regulate Binding of Voltage-gated Sodium and KCNQ2/3 Potassium Channels.
abstract: In many mammalian neurons, fidelity and robustness of action potential generation and conduction depends on the co-localization of voltage-gated sodium (Nav) and KCNQ2/3 potassium channel conductance at the distal axon initial segment (AIS) and nodes of Ranvier in a ratio of ∼40 to 1. Analogous "anchor" peptides within intracellular domains of vertebrate KCNQ2, KCNQ3, and Nav channel α-subunits bind Ankyrin-G (AnkG), thereby mediating concentration of those channels at AISs and nodes of Ranvier. Here, we show that the channel anchors bind at overlapping but distinct sites near the AnkG N terminus. In pulldown assays, the rank order of AnkG binding strength is Nav1.2 ≫ KCNQ3 > KCNQ2. Phosphorylation of KCNQ2 and KCNQ3 anchor domains by protein kinase CK2 (CK2) augments binding, as previously shown for Nav1.2. An AnkG fragment comprising ankyrin repeats 1 through 7 (R1-7) binds phosphorylated Nav or KCNQ anchors robustly. However, mutational analysis of R1-7 reveals differences in binding mechanisms. A smaller fragment, R1-6, exhibits much-diminished KCNQ3 binding but binds Nav1.2 well. Two lysine residues at the tip of repeat 2-3 β-hairpin (residues 105-106) are critical for Nav1.2 but not KCNQ3 channel binding. Another dibasic motif (residues Arg-47, Arg-50) in the repeat 1 front α-helix is crucial for KCNQ2/3 but not Nav1.2 binding. AnkG's alternatively spliced N terminus selectively gates access to those sites, blocking KCNQ but not Nav channel binding. These findings suggest that the 40:1 Nav:KCNQ channel conductance ratio at the distal AIS and nodes arises from the relative strength of binding to AnkG.
authors.affiliation: From the Molecular Neuropharmacology Laboratory, Department of Neurology, mingxuax@bcm.edu.
authors.forename: Mingxuan
authors.initials: M
authors.lastname: Xu
authors.affiliation: From the Molecular Neuropharmacology Laboratory, Department of Neurology, Department of Neuroscience, and Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030 ecc1@bcm.edu.
authors.forename: Edward C
authors.initials: EC
authors.lastname: Cooper
mesh_terms: D000595:Amino Acid Sequence; D017487:Ankyrins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001369:Axons / Q000737:chemistry / Q000378:metabolism; D047390:Casein Kinase II / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051658:KCNQ2 Potassium Channel / Q000235:genetics / Q000378:metabolism*; D051659:KCNQ3 Potassium Channel / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D062551:NAV1.2 Voltage-Gated Sodium Channel / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
chemical_list: C490613:ANK3 protein, human; D017487:Ankyrins; D051658:KCNQ2 Potassium Channel; C496914:KCNQ2 protein, human; D051659:KCNQ3 Potassium Channel; C496916:KCNQ3 protein, human; D062551:NAV1.2 Voltage-Gated Sodium Channel; D047390:Casein Kinase II
keywords: M-current; ankyrin; axon; axon initial segment; evolution; node of Ranvier; potassium channel; sodium channel