Abstract
SummaryX-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.
Highlights
Ion channels play important and diverse roles in the control of cellular electrical excitability as well as many ion transport pathways
The molecular forces that determine the thermodynamic stability of a particular state are poorly understood
We analyze the different Xray 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, statedependent 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
Summary
Ion channels play important and diverse roles in the control of cellular electrical excitability as well as many ion transport pathways. For the channel to become fully conductive, it is proposed that a further rotation of the transmembrane (TM) helices occurs to open the helix bundle crossing (HBC) gate as observed in the crystal structures of PIP2-bound Kir3.2 and the putative open-state structure of the prokaryotic KirBac3.1 (Bavro et al, 2012; Whorton and MacKinnon, 2011, 2013) These different structural states allow reconstruction of a possible gating pathway for the Kir channel, and we have chosen the pH-sensitive Kir1.1 (ROMK) channel to functionally probe this structural gating scheme
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