The Na+ channel inactivation gate is a molecular complex: a novel role of the COOH-terminal domain.
Electrical activity in nerve, skeletal muscle, and heart requires finely tuned activity of voltage-gated Na+ channels that open and then enter a nonconducting inactivated state upon depolarization. Inactivation occurs when the gate, the cytoplasmic loop linking domains III and IV of the alpha subunit, occludes the open pore. Subtle destabilization of inactivation by mutation is causally associated with diverse human disease. Here we show for the first time that the inactivation gate is a molecular complex consisting of the III-IV loop and the COOH terminus (C-T), which is necessary to stabilize the closed gate and minimize channel reopening. When this interaction is disrupted by mutation, inactivation is destabilized allowing a small, but important, fraction of channels to reopen, conduct inward current, and delay cellular repolarization. Thus, our results demonstrate for the first time that physiologically crucial stabilization of inactivation of the Na+ channel requires complex interactions of intracellular structures and indicate a novel structural role of the C-T domain in this process.
Motoike
Howard K
HK
Department of Pharmacology, College of Physicians & Surgeons of Columbia University, New York, NY 10032, USA.
Liu
Huajun
H
Glaaser
Ian W
IW
Yang
An-Suei
AS
Tateyama
Michihiro
M
Kass
Robert S
RS
D000595:Amino Acid Sequence; D002460:Cell Line; D006801:Humans; D015640:Ion Channel Gating / Q000235:genetics / Q000502:physiology*; D046911:Macromolecular Substances; D008564:Membrane Potentials / Q000235:genetics / Q000502:physiology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000235:genetics / Q000502:physiology*; D017434:Protein Structure, Tertiary / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000138:chemical synthesis / Q000502:physiology; D015222:Sodium Channels / Q000138:chemical synthesis / Q000235:genetics / Q000502:physiology*
D046911:Macromolecular Substances; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D015222:Sodium Channels