title: Repositioning of charged I-II loop amino acid residues within the electric field by beta subunit as a novel working hypothesis for the control of fast P/Q calcium channel inactivation.
abstract: We have investigated the contribution of the Ca(v)beta subunits to the process of inactivation dependent of the I-II loop of Ca(v)alpha(2.1). Two amino acid residues located in the alpha1 interaction domain (AID) of the I-II loop of Ca(v)alpha(2.1) (Arg(387) and Glu(388)) have been directly implicated in voltage-dependent inactivation of this channel. Various point mutations of these residues disrupt the interaction between the I-II loop and the III-IV loop, and thereby modify the inactivation properties of the channel by accelerating its kinetics and shifting the steady-state inactivation curve towards hyperpolarized potentials. A similar disruption is produced by Ca(v)beta(4) subunit association with the I-II loop. Moreover, in the presence of Ca(v)beta(4) subunit, introducing negatively charged residues at positions 387 or 388 slows inactivation kinetics down, whereas introducing positive charges has the opposite effect. The shift of the steady-state inactivation curve is also amino acid charge-dependent. In contrast, mutation of Arg(387) or Glu(388) does not alter the differential regulation of the different Ca(v)beta isoforms on inactivation. These results suggest that the expression of Ca(v)beta(4) alters the contribution of charged residues at positions 387 and 388 to inactivation. We discuss these results with regard to the actual hypotheses on the mechanisms of calcium channel inactivation. We introduce the working concept that Ca(v)beta-subunits produce a conformational repositioning of charged AID residues within the electric field.
authors.affiliation: INSERM Unité, CEA, Laboratoire Canaux Calciques, Fonctions et Pathologies, DRDC, 17 Rue des Martyrs, 38054 Grenoble Cedex 9, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Sandoz
authors.forename: Ignacio
authors.initials: I
authors.lastname: Lopez-Gonzalez
authors.forename: Séverine
authors.initials: S
authors.lastname: Stamboulian
authors.forename: Norbert
authors.initials: N
authors.lastname: Weiss
authors.forename: Christophe
authors.initials: C
authors.lastname: Arnoult
authors.forename: Michel
authors.initials: M
authors.lastname: De Waard
mesh_terms: D000409:Alanine / Q000235:genetics; D000818:Animals; D001120:Arginine / Q000235:genetics; D001345:Autoradiography / Q000379:methods; D020864:Calcium Channels, N-Type / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D004594:Electrophysiology; D018698:Glutamic Acid / Q000235:genetics; D007700:Kinetics; D008564:Membrane Potentials; D009433:Neural Inhibition; D009865:Oocytes; D010452:Peptide Biosynthesis; D017354:Point Mutation; D011487:Protein Conformation; D017434:Protein Structure, Tertiary / Q000502:physiology; D021122:Protein Subunits / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity; D013997:Time Factors; D014982:Xenopus laevis
chemical_list: D000409:Alanine; D001120:Arginine; D020864:Calcium Channels, N-Type; D018698:Glutamic Acid; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins