Potassium ion channel inactivation peptides

Voltage-gated K+ channels activate with depolarization of the membrane potential and subsequently inactivate. Shaker K+ channels inactivate very rapidly with a time constant of 2-3 ms. Aldrich and co-workers showed that this rapid inactivation arises from an amino(N)-terminal inactivation domain acting as a tethered particle that blocks the open channel. This mechanism is analogous to the “ball-and-chain” model proposed by Bezanilla and Armstrong for inactivation of Na+ channels. Removing the cytoplasmic N-terminal domain of Shaker K+ channels disrupts rapid inactivation, and internal application of a synthetic peptide corresponding to this domain (residues 1-20) restores inactivation. Several pieces of evidence indicate that block of Shaker channels by the inactivation domain and synthetic (ShB) peptide involves a single blocking particle physically occluding the pore. Recovery from inactivation and peptide block are speeded by raising the concentration of K+ on the opposite (external) side of the channel. Although the inactivation domain of the Shaker channel has a net positive charge, N-type inactivation shows no apparent voltage sensitivity over the range of -30 to +50 mV. 9 Peptide binding does show some voltage dependence, but increasing the net charge on the peptide does not increase this voltage dependence. Thus, the majority of the blocking particle does not appear to enter into the membrane electric field, but binds instead at the mouth of the pore.