title: Effect of S6 tail mutations on charge movement in Shaker potassium channels.
abstract: The cytoplasmic ends of the four S6 transmembrane segments of voltage-gated potassium channels converge in a bundle crossing that acts as the activation gate that opens in response to a depolarization. To explore whether the cytoplasmic extension of the S6 segment (the S6 tail) plays a role in coupling voltage sensor and activation gate movements, we examined the effect of cysteine substitution from residues N482 to T489 on the kinetics and voltage-dependence of S4 charge movement and on the kinetics of deactivation of ionic current. Among these mutants, F484C has the steepest voltage-dependent charge movement, the largest Q-V shift, and the fastest OFF gating currents. Further study of the residue at position 484, using mutagenesis and modification of F484C by cysteine reagents, suggests that aromaticity at this position is essential to maintain normal coupling. We used periodicity analysis to appraise the possibility that the S6 tail has an alpha-helical structure. Although we obtained an alpha-periodicity index of 2.41 for gating current parameters, a new randomization test produced an indecisive conclusion about the secondary structure of this region. Taken together, our results suggest that the tail end of S6 plays an important role in coupling between activation gating and charge movement.
authors.affiliation: Department of Physiology, Institute of Hyperexcitability, Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA.
authors.forename: Shinghua
authors.initials: S
authors.lastname: Ding
authors.forename: Richard
authors.initials: R
authors.lastname: Horn
mesh_terms: D002463:Cell Membrane Permeability / Q000235:genetics / Q000502:physiology; D003001:Cloning, Molecular; D003545:Cysteine / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D005583:Fourier Analysis; D006801:Humans; D015640:Ion Channel Gating / Q000235:genetics / Q000502:physiology*; D017136:Ion Transport / Q000235:genetics / Q000502:physiology; D007668:Kidney / Q000737:chemistry / Q000196:embryology / Q000502:physiology; D008564:Membrane Potentials / Q000235:genetics / Q000502:physiology; D016297:Mutagenesis, Site-Directed; D010507:Periodicity; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D012680:Sensitivity and Specificity; D051637:Shaker Superfamily of Potassium Channels
chemical_list: D015221:Potassium Channels; D021122:Protein Subunits; D051637:Shaker Superfamily of Potassium Channels; D003545:Cysteine