期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 104, 期 19, 页码 7904-7909出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0702638104
关键词
gating current; metal bridge; omega current; S-S bridge
资金
- NIGMS NIH HHS [R37 GM030376, R01 GM062342, GM062342, GM30376, R01 GM030376] Funding Source: Medline
it is now well established that the voltage-sensing S4 segment in voltage-dependent ion channels undergoes a conformational change in response to varying membrane potential. However, the magnitude of the movement of S4 relative to the membrane and the rest of the protein remains controversial. Here, by using histidine scanning mutagenesis in the Shaker K channel, we identified mutants I241H (S1 segment) and I287H (S2 segment) that generate inward currents at hyperpolarized potentials, suggesting that these residues are part of a hydrophobic plug that separates the water-accessible crevices. Additional experiments with substituted cysteine residues showed that, at hyperpolarized potentials, both I241C and I287C can spontaneously form disulphide and metal bridges with R362C, the position of the first charge-carrying residue in S4. These results constrain unambiguously the closed-state positions of the S4 segment with respect to the S1 and S2 segments, which are known to undergo little or no movement during gating. To satisfy these constraints, the S4 segment must undergo an axial rotation of approximate to 180 degrees and a transmembrane (vertical) movement of approximate to 6.5 A at the level of R362 in going from the open to the closed state of the channel, moving the gating charge across a focused electric field.
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