Dataset Information

Understanding the conformational motions of RCK gating rings.

ABSTRACT: Regulator of conduction of K+ (RCK) domains are ubiquitous regulators of channel and transporter activity in prokaryotes and eukaryotes. In humans, RCK domains form an integral component of large-conductance calcium-activated K channels (BK channels), key modulators of nerve, muscle, and endocrine cell function. In this review, we explore how the study of RCK domains in bacterial and human channels has contributed to our understanding of the structural basis of channel function. This knowledge will be critical in identifying mechanisms that underlie BK channelopathies that lead to epilepsy and other diseases, as well as regions of the channel that might be successfully targeted to treat such diseases.

SUBMITTER: Giraldez T

PROVIDER: S-EPMC5379921 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Understanding the conformational motions of RCK gating rings.

Giraldez Teresa T Rothberg Brad S BS

The Journal of general physiology 20170228 4

Regulator of conduction of K<sup>+</sup> (RCK) domains are ubiquitous regulators of channel and transporter activity in prokaryotes and eukaryotes. In humans, RCK domains form an integral component of large-conductance calcium-activated K channels (BK channels), key modulators of nerve, muscle, and endocrine cell function. In this review, we explore how the study of RCK domains in bacterial and human channels has contributed to our understanding of the structural basis of channel function. This ...[more]

PMID: 28246116

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Project description:Ionotropic glutamate receptors (iGluRs) are tetrameric ligand-gated ion channels essential to all aspects of brain function, including higher order processes such as learning and memory. For decades, electrophysiology was the primary means for characterizing the function of iGluRs and gaining mechanistic insight. Since the turn of the century, structures of isolated water-soluble domains and transmembrane-domain-containing constructs have provided the basis for formulating mechanistic hypotheses. Because these structures only represent sparse, often incomplete snapshots during iGluR activation, significant gaps in knowledge remain regarding structures, energetics, and dynamics of key substates along the functional processes. Some of these gaps have recently been filled by molecular dynamics simulations and theoretical modeling. In this Account, I describe our work in the latter arena toward characterizing iGluR gating motions and developing a formalism for calculating thermodynamic and kinetic properties of stationary gating. The structures of iGluR subunits have a highly modular architecture, in which the ligand-binding domain and the transmembrane domain are well separated and connected by flexible linkers. The ligand-binding domain in turn is composed of two subdomains. During activation, agonist binding induces the closure of the intersubdomain cleft. The cleft closure leads to the outward pulling of a linker tethered to the extracellular terminus of the major pore-lining helix of the transmembrane domain, thereby opening the channel. This activation model based on molecular dynamics simulations was validated by residue-specific information from electrophysiological data on cysteine mutants. A further critical test was made through introducing glycine insertions in the linker. Molecular dynamics simulations showed that, with lengthening by glycine insertions, the linker became less effective in pulling the pore-lining helix, leading to weaker stabilization of the channel-open state. In full agreement, single-channel recordings showed that the channel open probability decreased progressively as the linker was lengthened by glycine insertions. Crystal structures of ligand-binding domains showing different degrees of cleft closure between full and partial agonists suggested a simple mechanism for one subtype of iGluRs, but mysteries surrounded a second subtype, where the ligand-binding domains open to similar degrees when bound with either full or partial agonists. Our free energy simulations now suggest that broadening of the free energy basin for cleft closure is a plausible solution. A theoretical basis for these mechanistic hypotheses on partial agonisms was provided by a model for the free energy surface of a full receptor, where the stabilization by cleft closure is transmitted via the linker to the channel-open state. This model can be implemented by molecular dynamics simulations to predict thermodynamic and kinetics properties of stationary gating that are amenable to direct test by single-channel recordings. Close integration between computation and electrophysiology holds great promises in revealing the conformations of key substates in functional processes and the mechanisms of disease-associated mutations.

Dataset Information

Understanding the conformational motions of RCK gating rings.

Publications

Understanding the conformational motions of RCK gating rings.

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