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Voltage sensitivity and gating charge in Shaker and Shab family potassium channels.

Islas LD, Sigworth FJ - J. Gen. Physiol. (1999)

Bottom Line: We find that Shab has a relatively small gating charge, approximately 7.5 e(o).Surprisingly, the corresponding mammalian delayed rectifier Kv2.1, which has the same complement of charged residues in the S2, S3, and S4 segments, has a gating charge of 12.5 e(o), essentially equal to that of Shaker and Kv1.1.Evidence for very strong coupling between charge movement and channel opening is seen in two channel types, with the probability of voltage-independent channel openings measured to be below 10(-9) in Shaker and below 4 x 10(-8) in Kv2.1.

View Article: PubMed Central - PubMed

Affiliation: Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.

ABSTRACT
The members of the voltage-dependent potassium channel family subserve a variety of functions and are expected to have voltage sensors with different sensitivities. The Shaker channel of Drosophila, which underlies a transient potassium current, has a high voltage sensitivity that is conferred by a large gating charge movement, approximately 13 elementary charges. A Shaker subunit's primary voltage-sensing (S4) region has seven positively charged residues. The Shab channel and its homologue Kv2.1 both carry a delayed-rectifier current, and their subunits have only five positively charged residues in S4; they would be expected to have smaller gating-charge movements and voltage sensitivities. We have characterized the gating currents and single-channel behavior of Shab channels and have estimated the charge movement in Shaker, Shab, and their rat homologues Kv1.1 and Kv2.1 by measuring the voltage dependence of open probability at very negative voltages and comparing this with the charge-voltage relationships. We find that Shab has a relatively small gating charge, approximately 7.5 e(o). Surprisingly, the corresponding mammalian delayed rectifier Kv2.1, which has the same complement of charged residues in the S2, S3, and S4 segments, has a gating charge of 12.5 e(o), essentially equal to that of Shaker and Kv1.1. Evidence for very strong coupling between charge movement and channel opening is seen in two channel types, with the probability of voltage-independent channel openings measured to be below 10(-9) in Shaker and below 4 x 10(-8) in Kv2.1.

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Sequence alignment of the S2–S4 regions of the four voltage-gated potassium channels in this study. The proposed membrane spanning regions are indicated by lines. Bold letters indicate conserved charged residues. Numbers at the beginning and end of each segment refer to amino acid numbering. Shaker numbering corresponds to the Shaker B1 splice variant (Schwarz et al. 1988). Sequences are taken from Chandy and Gutman 1995.
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Figure 1: Sequence alignment of the S2–S4 regions of the four voltage-gated potassium channels in this study. The proposed membrane spanning regions are indicated by lines. Bold letters indicate conserved charged residues. Numbers at the beginning and end of each segment refer to amino acid numbering. Shaker numbering corresponds to the Shaker B1 splice variant (Schwarz et al. 1988). Sequences are taken from Chandy and Gutman 1995.

Mentions: In this paper, we incorporate these advances to the limiting-slope method and apply it to the determination of charge movements in homomeric channels encoded by the Drosophila potassium channel genes Shaker and Shab, and from the rat homologues Kv1.1 and Kv2.1. A comparison of these channel types is interesting in view of their differing amino acid sequences (Fig. 1). Shaker and Kv1.1 both have seven basic residues in the S4 region, while Shab and Kv2.1 have five.


Voltage sensitivity and gating charge in Shaker and Shab family potassium channels.

Islas LD, Sigworth FJ - J. Gen. Physiol. (1999)

Sequence alignment of the S2–S4 regions of the four voltage-gated potassium channels in this study. The proposed membrane spanning regions are indicated by lines. Bold letters indicate conserved charged residues. Numbers at the beginning and end of each segment refer to amino acid numbering. Shaker numbering corresponds to the Shaker B1 splice variant (Schwarz et al. 1988). Sequences are taken from Chandy and Gutman 1995.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2230542&req=5

Figure 1: Sequence alignment of the S2–S4 regions of the four voltage-gated potassium channels in this study. The proposed membrane spanning regions are indicated by lines. Bold letters indicate conserved charged residues. Numbers at the beginning and end of each segment refer to amino acid numbering. Shaker numbering corresponds to the Shaker B1 splice variant (Schwarz et al. 1988). Sequences are taken from Chandy and Gutman 1995.
Mentions: In this paper, we incorporate these advances to the limiting-slope method and apply it to the determination of charge movements in homomeric channels encoded by the Drosophila potassium channel genes Shaker and Shab, and from the rat homologues Kv1.1 and Kv2.1. A comparison of these channel types is interesting in view of their differing amino acid sequences (Fig. 1). Shaker and Kv1.1 both have seven basic residues in the S4 region, while Shab and Kv2.1 have five.

Bottom Line: We find that Shab has a relatively small gating charge, approximately 7.5 e(o).Surprisingly, the corresponding mammalian delayed rectifier Kv2.1, which has the same complement of charged residues in the S2, S3, and S4 segments, has a gating charge of 12.5 e(o), essentially equal to that of Shaker and Kv1.1.Evidence for very strong coupling between charge movement and channel opening is seen in two channel types, with the probability of voltage-independent channel openings measured to be below 10(-9) in Shaker and below 4 x 10(-8) in Kv2.1.

View Article: PubMed Central - PubMed

Affiliation: Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.

ABSTRACT
The members of the voltage-dependent potassium channel family subserve a variety of functions and are expected to have voltage sensors with different sensitivities. The Shaker channel of Drosophila, which underlies a transient potassium current, has a high voltage sensitivity that is conferred by a large gating charge movement, approximately 13 elementary charges. A Shaker subunit's primary voltage-sensing (S4) region has seven positively charged residues. The Shab channel and its homologue Kv2.1 both carry a delayed-rectifier current, and their subunits have only five positively charged residues in S4; they would be expected to have smaller gating-charge movements and voltage sensitivities. We have characterized the gating currents and single-channel behavior of Shab channels and have estimated the charge movement in Shaker, Shab, and their rat homologues Kv1.1 and Kv2.1 by measuring the voltage dependence of open probability at very negative voltages and comparing this with the charge-voltage relationships. We find that Shab has a relatively small gating charge, approximately 7.5 e(o). Surprisingly, the corresponding mammalian delayed rectifier Kv2.1, which has the same complement of charged residues in the S2, S3, and S4 segments, has a gating charge of 12.5 e(o), essentially equal to that of Shaker and Kv1.1. Evidence for very strong coupling between charge movement and channel opening is seen in two channel types, with the probability of voltage-independent channel openings measured to be below 10(-9) in Shaker and below 4 x 10(-8) in Kv2.1.

Show MeSH
Related in: MedlinePlus