Participation of the S4 voltage sensor in the Mg2+-dependent activation of large conductance (BK) K+ channels.
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.
Hu
Lei
L
Cardiac Bioelectricity Research and Training Center and Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106, USA.
Shi
Jingyi
J
Ma
Zhongming
Z
Krishnamoorthy
Gayathri
G
Sieling
Fred
F
Zhang
Guangping
G
Horrigan
Frank T
FT
Cui
Jianmin
J
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D015640:Ion Channel Gating; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D008274:Magnesium / Q000494:pharmacology*; D051379:Mice; D008969:Molecular Sequence Data; D015221:Potassium Channels / Q000737:chemistry* / Q000502:physiology*; D024681:Potassium Channels, Calcium-Activated; D011487:Protein Conformation; D013329:Structure-Activity Relationship
C465449:Kcnma1 protein, mouse; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D008274:Magnesium; D002118:Calcium