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Binding of anionic lipids to at least three nonannular sites on the potassium channel KcsA is required for channel opening

Binding of anionic lipids to at least three nonannular sites on the potassium channel KcsA is required for channel opening
Binding of anionic lipids to at least three nonannular sites on the potassium channel KcsA is required for channel opening
In addition to the annular or boundary lipids that surround the transmembrane surface of the potassium channel KcsA from Streptomyces lividans, x-ray crystallographic studies have detected one anionic lipid molecule bound at each protein-protein interface in the homotetrameric structure, at sites referred to as nonannular sites. The binding constant for phosphatidylglycerol at the nonannular sites has been determined using fluorescence quenching methods with a mutant of KcsA lacking the normal three lipid-exposed Trp residues. Binding is weak, with a binding constant of 0.42±0.06 in units of mol fraction, implying that the nonannular sites will only be ?70% occupied in bilayers of 100% phosphatidylglycerol. However, the nonannular sites show high selectivity for anionic lipids over zwitterionic lipids, and it is suggested that a change in packing at the protein-protein interface leads to a closing of the nonannular binding site in the unbound state. Increasing the anionic lipid content of the membrane leads to a large increase in open channel probability, from ?2.5% in the presence of 25mol % phosphatidylglycerol to ?62% in 100mol % phosphatidylglycerol. The relationship between open channel probability and phosphatidylglycerol content shows cooperativity. The data are consistent with a model in which three or four of the four nonannular sites in the KcsA homotetramer have to be occupied by anionic lipid for the channel to open. The conductance of the open channel increases with increasing concentration of anionic lipid, an effect possibly due to effects of anionic lipid on the concentration of K+ close to the membrane surface.
0006-3495
1689-1698
Marius, Phedra
f5bf8a27-2332-4d04-a45b-4b2677fcc865
Zagnoni, Michele
abfb96d5-0d3c-4b23-864b-b1212f6d5a42
Sandison, Mairi E.
90477e5a-2af6-44b1-8ea8-ae4515594c60
East, J. Malcolm
9fe7f794-1d89-4935-9a99-b831d786056e
Morgan, Hywel
de00d59f-a5a2-48c4-a99a-1d5dd7854174
Lee, Anthony G.
0891914c-e0e2-4ee1-b43e-1b70eb072d8e
Marius, Phedra
f5bf8a27-2332-4d04-a45b-4b2677fcc865
Zagnoni, Michele
abfb96d5-0d3c-4b23-864b-b1212f6d5a42
Sandison, Mairi E.
90477e5a-2af6-44b1-8ea8-ae4515594c60
East, J. Malcolm
9fe7f794-1d89-4935-9a99-b831d786056e
Morgan, Hywel
de00d59f-a5a2-48c4-a99a-1d5dd7854174
Lee, Anthony G.
0891914c-e0e2-4ee1-b43e-1b70eb072d8e

Marius, Phedra, Zagnoni, Michele, Sandison, Mairi E., East, J. Malcolm, Morgan, Hywel and Lee, Anthony G. (2008) Binding of anionic lipids to at least three nonannular sites on the potassium channel KcsA is required for channel opening. Biophysical Journal, 94 (5), 1689-1698. (doi:10.1529/biophysj.107.117507).

Record type: Article

Abstract

In addition to the annular or boundary lipids that surround the transmembrane surface of the potassium channel KcsA from Streptomyces lividans, x-ray crystallographic studies have detected one anionic lipid molecule bound at each protein-protein interface in the homotetrameric structure, at sites referred to as nonannular sites. The binding constant for phosphatidylglycerol at the nonannular sites has been determined using fluorescence quenching methods with a mutant of KcsA lacking the normal three lipid-exposed Trp residues. Binding is weak, with a binding constant of 0.42±0.06 in units of mol fraction, implying that the nonannular sites will only be ?70% occupied in bilayers of 100% phosphatidylglycerol. However, the nonannular sites show high selectivity for anionic lipids over zwitterionic lipids, and it is suggested that a change in packing at the protein-protein interface leads to a closing of the nonannular binding site in the unbound state. Increasing the anionic lipid content of the membrane leads to a large increase in open channel probability, from ?2.5% in the presence of 25mol % phosphatidylglycerol to ?62% in 100mol % phosphatidylglycerol. The relationship between open channel probability and phosphatidylglycerol content shows cooperativity. The data are consistent with a model in which three or four of the four nonannular sites in the KcsA homotetramer have to be occupied by anionic lipid for the channel to open. The conductance of the open channel increases with increasing concentration of anionic lipid, an effect possibly due to effects of anionic lipid on the concentration of K+ close to the membrane surface.

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Published date: March 2008
Organisations: Biological Sciences

Identifiers

Local EPrints ID: 142821
URI: https://eprints.soton.ac.uk/id/eprint/142821
ISSN: 0006-3495
PURE UUID: c493fad0-7d18-4f11-a3c6-6adbded4d6ee
ORCID for Hywel Morgan: ORCID iD orcid.org/0000-0003-4850-5676

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Date deposited: 01 Apr 2010 15:57
Last modified: 10 Sep 2019 00:45

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