Protein Rearrangements Underlying Slow Inactivation of the
Shaker K+ Channel
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Authors: | E Loots EY Isacoff |
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Institution: | From the Department of Molecular & Cell Biology, University of California, Berkeley, Berkeley, California 94720-3200 |
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Abstract: | Voltage-dependent ion channels transduce changes in the membrane electric field into protein rearrangements that gate their transmembrane ion permeation pathways. While certain molecular elements of the
voltage sensor and gates have been identified, little is known about either the nature of their conformational rearrangements or about how the voltage sensor is coupled to the gates. We used voltage clamp fluorometry to examine the voltage sensor (S4) and pore region (P-region) protein motions that underlie the slow inactivation of the
Shaker K+ channel. Fluorescent probes in both the P-region and S4 changed emission intensity in parallel with the
onset and recovery of slow inactivation, indicative of local protein rearrangements in this gating process. Two sequential rearrangements were observed, with channels first entering the P-type, and then the C-type inactivated
state. These forms of inactivation appear to be mediated by a single gate, with P-type inactivation closing the gate
and C-type inactivation stabilizing the gate''s closed conformation. Such a stabilization was due, at least in part, to
a slow rearrangement around S4 that stabilizes S4 in its activated transmembrane position. The fluorescence reports of S4 and P-region fluorophore are consistent with an increased interaction of the voltage sensor and inactivation gate upon gate closure, offering insight into how the voltage-sensing apparatus is coupled to a channel
gate. |
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Keywords: | inactivation fluorescence K+ channel pore S4 |
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