title: State-dependent inter-repeat contacts of exceptionally conserved asparagines in the inner helices of sodium and calcium channels.
abstract: Voltage-gated sodium and calcium channels play key roles in the physiology of excitable cells. The alpha-1 subunit of these channels folds from a polypeptide chain of four homologous repeats. In each repeat, the cytoplasmic halves of the pore-lining helices contain exceptionally conserved asparagines. Such conservation implies important roles, which are unknown. Mutations of the asparagines affect activation and inactivation gating as well as the action of pore-targeting ligands, including local anesthetics and steroidal agonists batrachotoxin and veratridine. In the absence of the open-channel structures, underlying mechanisms are unclear. Here, we modeled the pore module of Cav1.2 and Nav1.4 channels and their mutants in the open and closed states using the X-ray structures of potassium and sodium channels as templates. The energy of each model was Monte Carlo-minimized. The asparagines do not face the pore in the modeled states. In the open-channel models, the asparagine residue in a given repeat forms an inter-repeat H-bond with a polar residue, which is typically nine positions downstream from the conserved asparagine in the preceding repeat. The H-bonds, which are strengthened by surrounding hydrophobic residues, would stabilize the open channel and shape the open-pore geometry. According to our calculation, the latter is much more sensitive to mutations of the asparagines than the closed-pore geometry. Rearrangement of inter-repeat contacts may explain effects of these mutations on the voltage dependence of activation and inactivation and action of pore-targeting ligands.
authors.affiliation: Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia.
authors.forename: Denis B
authors.initials: DB
authors.lastname: Tikhonov
authors.forename: Iva
authors.initials: I
authors.lastname: Bruhova
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Garden
authors.forename: Boris S
authors.initials: BS
authors.lastname: Zhorov
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001216:Asparagine / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017124:Conserved Sequence; D006801:Humans; D015640:Ion Channel Gating; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D009154:Mutation; D062553:NAV1.4 Voltage-Gated Sodium Channel / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary
chemical_list: D020746:Calcium Channels, L-Type; C419385:L-type calcium channel alpha(1C); D062553:NAV1.4 Voltage-Gated Sodium Channel; D001216:Asparagine
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