We recently examined how Kir1.1, an inwardly-rectifying potassium channel that is found in the kidneys, opens and closes in response to being stimulated by changes in pH or the presence of absence of PIP2, a signalling lipid [1]. The key result of that paper was that we could identify several networks of residues that came together to form one large gate when the channel was open. In this addendum paper, we examine how mutating several of these residues affected the kinetics of gating [2]. By comparing the on- and off-rates we are able to infer that the transition state more closely resembles that pre-open, rather than open, state. This paper is open access and is freely available to download.
References
[1] M. K. Bollepalli, P. W. Fowler, M. Rapedius, L. Shang, M. S. P. Sansom, S. J. Tucker, and T. Baukrowitz, “State-dependent network connectivity determines gating in a K+ channel.,�? Structure, vol. 22, pp. 1037-1046, 2014.
@article{Bollepalli2014,
abstract = {X-ray crystallography has provided tremendous insight into the different structural states of membrane proteins and, in particular, of ion channels. However, the molecular forces that determine the thermodynamic stability of a particular state are poorly understood. Here we analyze the different X-ray structures of an inwardly rectifying potassium channel (Kir1.1) in relation to functional data we obtained for over 190 mutants in Kir1.1. This mutagenic perturbation analysis uncovered an extensive, state-dependent network of physically interacting residues that stabilizes the pre-open and open states of the channel, but fragments upon channel closure. We demonstrate that this gating network is an important structural determinant of the thermodynamic stability of these different gating states and determines the impact of individual mutations on channel function. These results have important implications for our understanding of not only K+ channel gating but also the more general nature of conformational transitions that occur in other allosteric proteins.},
author = {Bollepalli, Murali K. and Fowler, Philip W. and Rapedius, Markus and Shang, Lijun and Sansom, Mark S P and Tucker, Stephen J. and Baukrowitz, Thomas},
doi = {10.1016/j.str.2014.04.018},
journal = {Structure},
pages = {1037-1046},
pmid = {24980796},
title = {{State-dependent network connectivity determines gating in a K+ channel.}},
volume = {22},
year = {2014}
}[2] P. W. Fowler, M. K. Bollepalli, M. Rapedius, E. Nematian, L. Shang, M. S. P. Sansom, S. J. Tucker, and T. Baukrowitz, “Insights into the structural nature of the transition state in the Kir channel gating pathway,�? Channels, vol. 8, pp. 551-555, 2014.
@article{Fowler2014,
abstract = {In a previous study we identified an extensive gating network within the inwardly rectifying Kir1.1 (ROMK) channel by combining systematic scanning mutagenesis and functional analysis with structural models of the channel in the closed, pre-open and open states. This extensive network appeared to stabilize the open and pre-open states, but the network fragmented upon channel closure. In this study we have analyzed the gating kinetics of different mutations within key parts of this gating network. These results suggest that the structure of the transition state (TS), which connects the pre-open and closed states of the channel, more closely resembles the structure of the pre-open state. Furthermore, the G-loop, which occurs at the centre of this extensive gating network, appears to become unstructured in the TS because mutations within this region have a ‘catalytic’ effect upon the channel gating kinetics.},
author = {Fowler, Philip W and Bollepalli, Murali K. and Rapedius, Markus and Nematian, Ehsan and Shang, Lijun and Sansom, Mark S. P. and Tucker, Stephen J. and Baukrowitz, Thomas},
doi = {10.4161/19336950.2014.962371},
journal = {Channels},
pages = {551-555},
title = {{Insights into the structural nature of the transition state in the Kir channel gating pathway}},
volume = {8},
year = {2014}
}