title: Modelling of the III-IV loop, a domain involved in calcium channel Ca(v)2.1 inactivation, highlights a structural homology with the gamma subunit of G proteins.
abstract: We have modelled the conformation of the III-IV loop of the Ca(v)2.1 subunit of P/Q calcium channels, a loop that is implicated in fast voltage-dependent inactivation. Change in channel inactivation requires its direct interaction with the I-II loop. This interaction occurs with an affinity in the order of 70 nm. Intracellular injection of a 40-mer III-IV loop-derived peptide produces an increase in the rate of fast inactivation. This alteration in channel kinetic is also accompanied by a hyperpolarizing shift in the steady-state voltage-dependence of inactivation. None of these effects are observed in the presence of a beta subunit, suggesting the existence of a competitive mechanism of action between the beta subunit and the III-IV loop. Amino acid sequence comparison using BLAST reveals that the III-IV loop shares 53% identity with the gamma subunit of G proteins. Because of the pivotal contribution of the III-IV loop to inactivation, an atomic model of the III-IV loop was generated by both homology modelling and molecular mechanics calculations. Using the X-ray structures of the betagamma dimer of the heterotrimeric G-proteins as templates, the III-IV loop is predicted to contain a well-structured alpha-helix at the amino-terminus with both the N- and C-termini having the same orientation in the plane of the inner lipid bilayer. We provide a hypothetical working model in which we propose that the III-IV loop interacts with the I-II loop via its Gbetagamma binding domain.
authors.affiliation: Laboratoire de Biochimie, CNRS UMR 6560, Faculté de Médecine Nord, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Fathallah
authors.forename: Guillaume
authors.initials: G
authors.lastname: Sandoz
authors.forename: Kamel
authors.initials: K
authors.lastname: Mabrouk
authors.forename: Sandrine
authors.initials: S
authors.lastname: Geib
authors.forename: Julie
authors.initials: J
authors.lastname: Urbani
authors.forename: Michel
authors.initials: M
authors.lastname: Villaz
authors.forename: Michel
authors.initials: M
authors.lastname: Ronjat
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Sabatier
authors.forename: Michel
authors.initials: M
authors.lastname: De Waard
mesh_terms: D000595:Amino Acid Sequence / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D020864:Calcium Channels, N-Type / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005260:Female; D020962:Heterotrimeric GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008954:Models, Biological; D008969:Molecular Sequence Data; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009865:Oocytes; D010446:Peptide Fragments / Q000494:pharmacology; D011485:Protein Binding / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000187:drug effects / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000187:drug effects / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D014982:Xenopus laevis
chemical_list: D020864:Calcium Channels, N-Type; D020962:Heterotrimeric GTP-Binding Proteins; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins