Inactivation and recovery in Kv1.4 K+ channels: lipophilic interactions at the intracellular mouth of the pore.
C-type inactivation is present in many voltage-gated potassium channels and is probably related to 'slow' inactivation in calcium and sodium channels. The mechanisms underlying C-type inactivation are unclear, but it is sensitive to mutations on both the extra- and intracellular sides of the channel. We used an N-terminal deleted channel with a valine to alanine point mutation at the intracellular side of S6 (fKv1.4[V561A]DeltaN). This construct alters recovery from inactivation and inverts the relationship between C-type inactivation and [K(+)](o). We used this inverted relationship to examine C-type inactivation and coupling mechanisms between N- and C-type inactivation. The valine to alanine mutation reduces the channel's affinity for both quinidine and the N-terminal domain. However, binding of the N-terminal or quinidine restores normal recovery from inactivation. This suggests that coupling between N- and C-type inactivation is dominated by allosteric mechanisms. The permeation mechanism, driven by a reduction in permeant [K(+)](o) following pore block (which would retard C-type inactivation), contributes minimally to coupling in these channels. We propose that the cytoplasmic half of S6 forms part of the N-terminal binding site, as previously predicted from X-ray crystallography studies in the distantly related KcsA channel. Binding of the N-terminal domain or a positively charged lipophilic compound such as quinidine interacts with the hydrophobic moieties on S6 in the bound state. This binding can orientate S6 into a conformation which resembles the normal C-type inactivated state. This is the probable mechanism by which drug or N-terminal binding increases the rate of C-type inactivation via an allosteric mechanism.
Bett
Glenna C L
GC
Department of Physiology and Biophysics, 124 Sherman Hall, State University of New York at Buffalo, Buffalo, NY 14214-3005, USA.
Rasmusson
Randall L
RL
D000409:Alanine; D000494:Allosteric Regulation; D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D003593:Cytoplasm / Q000378:metabolism; D005260:Female; D017353:Gene Deletion; D007424:Intracellular Fluid / Q000378:metabolism*; D051665:Kv1.4 Potassium Channel; D008968:Molecular Conformation; D009865:Oocytes; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D010539:Permeability; D017354:Point Mutation; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated; D011802:Quinidine / Q000378:metabolism*; D014633:Valine; D014982:Xenopus laevis
D051665:Kv1.4 Potassium Channel; D010446:Peptide Fragments; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D014633:Valine; D011802:Quinidine; D000409:Alanine