Ligand-gated ion channels are oligomers containing several binding sites for the ligands. However, the signal transmission from the ligand binding site to the pore has not yet been fully elucidated for any of these channels. In heteromeric channels, the situation is even more complex than in homomeric channels. Using published data for concatamers of heteromeric cyclic nucleotide–gated channels, we show that, on theoretical grounds, multiple functional parameters of the individual subunits can be determined with high precision. The main components of our strategy are (1) the generation of a defined subunit composition by concatenating multiple subunits, (2) the construction of 16 concatameric channels, which differ in systematically permutated binding sites, (3) the determination of respectively differing concentration–activation relationships, and (4) a complex global fit analysis with corresponding intimately coupled Markovian state models. The amount of constraints in this approach is exceedingly high. Furthermore, we propose a stochastic fit analysis with a scaled unitary start vector of identical elements to avoid any bias arising from a specific start vector. Our approach enabled us to determine 23 free parameters, including 4 equilibrium constants for the closed–open isomerizations, 4 disabling factors for the mutations of the different subunits, and 15 virtual equilibrium-association constants in the context of a 4-D hypercube. From the virtual equilibrium-association constants, we could determine 32 equilibrium-association constants of the subunits at different degrees of ligand binding. Our strategy can be generalized and is therefore adaptable to other ion channels.
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6 June 2022
Article|
April 29 2022
A strategy for determining the equilibrium constants for heteromeric ion channels in a complex model
Klaus Benndorf
,
1Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany
Correspondence to Klaus Benndorf: Klaus.Benndorf@med.uni-jena.de
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Thomas Eick
,
Thomas Eick
1Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany
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Christian Sattler
,
Christian Sattler
1Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany
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Ralf Schmauder
,
Ralf Schmauder
1Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany
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Eckhard Schulz
Eckhard Schulz
2Schmalkalden University of Applied Sciences, Faculty of Electrical Engineering, Schmalkalden, Germany
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1Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany
Thomas Eick
1Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany
Christian Sattler
1Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany
Ralf Schmauder
1Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany
Eckhard Schulz
2Schmalkalden University of Applied Sciences, Faculty of Electrical Engineering, Schmalkalden, Germany
Correspondence to Klaus Benndorf: Klaus.Benndorf@med.uni-jena.de
Received:
October 21 2021
Revision Received:
February 11 2022
Accepted:
March 18 2022
Online Issn: 1540-7748
Print Issn: 0022-1295
Funding
Funder(s):
Deutsche Forschungsgemeinschaft
- Award Id(s): project P2
© 2022 Benndorf et al.
2022
This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms/). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 International license, as described at https://creativecommons.org/licenses/by-nc-sa/4.0/).
J Gen Physiol (2022) 154 (6): e202113041.
Article history
Received:
October 21 2021
Revision Received:
February 11 2022
Accepted:
March 18 2022
Citation
Klaus Benndorf, Thomas Eick, Christian Sattler, Ralf Schmauder, Eckhard Schulz; A strategy for determining the equilibrium constants for heteromeric ion channels in a complex model. J Gen Physiol 6 June 2022; 154 (6): e202113041. doi: https://doi.org/10.1085/jgp.202113041
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