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Participation of the S4 voltage sensor in the Mg2+-dependent activation of large conductance (BK) K+ channels

By Lei Hu, Jingyi Shi, Zhongming Ma, Gayathri Krishnamoorthy, Fred Sieling, Guangping Zhang, Frank T. Horrigan and Jianmin Cui

Abstract

The S4 transmembrane segment is the primary voltage sensor in voltage-dependent ion channels. Its movement in response to changes in membrane potential leads to the opening of the activation gate, which is formed by a separate structural component, the S6 segment. Here we show in voltage-, Ca2+-, and Mg2+-dependent, large conductance K+ channels that the S4 segment participates not only in voltage- but also Mg2+-dependent activation. Mutations in S4 and the S4-S5 linker alter voltage-dependent activation and have little or no effect on activation by micromolar Ca2+. However, a subset of these mutations in the C-terminal half of S4 and in the S4-S5 linker either reduce or abolish the Mg2+ sensitivity of channel gating. Cysteine residues substituted into positions R210 and R213, marking the boundary between S4 mutations that alter Mg2+ sensitivity and those that do not, are accessible to a modifying reagent [sodium (2-sulfonatoethyl)methane-thiosulfonate] (MTSES) from the extracellular and intracellular side of the membrane, respectively, at -80 mV. This implies that interactions between S4 and a cytoplasmic domain may be involved in Mg2+-dependent activation. These results indicate that the voltage sensor is critical for Mg2+-dependent activation and the coupling between the voltage sensor and channel gate is a converging point for voltage- and Mg2+-dependent activation pathways

Topics: Biological Sciences
Publisher: National Academy of Sciences
Year: 2003
DOI identifier: 10.1073/pnas.1834300100
OAI identifier: oai:pubmedcentral.nih.gov:193588
Provided by: PubMed Central
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