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Direct Pore Binding as a Mechanism for Isoflurane Inhibition of the Pentameric Ligand-gated Ion Channel ELIC.

Chen Q, Kinde MN, Arjunan P, Wells MM, Cohen AE, Xu Y, Tang P - Sci Rep (2015)

Bottom Line: Electrophysiology measurements with a single-point mutation at position 6' or 13' support the notion that binding at these sites renders isoflurane inhibition.Molecular dynamics simulations suggested that isoflurane binding was more stable in the resting than in a desensitized pore conformation.This study presents compelling evidence for a direct pore-binding mechanism of isoflurane inhibition, which has a general implication for inhibitory action of general anesthetics on pLGICs.

View Article: PubMed Central - PubMed

Affiliation: Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, 15260, USA.

ABSTRACT
Pentameric ligand-gated ion channels (pLGICs) are targets of general anesthetics, but molecular mechanisms underlying anesthetic action remain debatable. We found that ELIC, a pLGIC from Erwinia chrysanthemi, can be functionally inhibited by isoflurane and other anesthetics. Structures of ELIC co-crystallized with isoflurane in the absence or presence of an agonist revealed double isoflurane occupancies inside the pore near T237(6') and A244(13'). A pore-radius contraction near the extracellular entrance was observed upon isoflurane binding. Electrophysiology measurements with a single-point mutation at position 6' or 13' support the notion that binding at these sites renders isoflurane inhibition. Molecular dynamics simulations suggested that isoflurane binding was more stable in the resting than in a desensitized pore conformation. This study presents compelling evidence for a direct pore-binding mechanism of isoflurane inhibition, which has a general implication for inhibitory action of general anesthetics on pLGICs.

No MeSH data available.


Related in: MedlinePlus

Isoflurane binding is more stable in the closed channel.Probabilities of finding an isoflurane molecule (center of mass) in molecular dynamics (MD) simulations at position z along the pore axis, P(z), and at the distance r from the pore axis, P(r), were calculated for (a,c) the closed channel and (b,d) a desensitized channel. A probability is defined as the ratio of the number of snapshots where isoflurane was found at the position z or at the distance r to the total snapshots chosen from the simulation. The bin widths of 1 Å and 0.5 Å were used for position z and distance r, respectively. Isoflurane motion in each pore conformation was evaluated every 0.1 ns from 100 ns simulations. Color indicates starting positions of isoflurane, 6′ (red) or 13′ (blue), in the MD simulations.
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f5: Isoflurane binding is more stable in the closed channel.Probabilities of finding an isoflurane molecule (center of mass) in molecular dynamics (MD) simulations at position z along the pore axis, P(z), and at the distance r from the pore axis, P(r), were calculated for (a,c) the closed channel and (b,d) a desensitized channel. A probability is defined as the ratio of the number of snapshots where isoflurane was found at the position z or at the distance r to the total snapshots chosen from the simulation. The bin widths of 1 Å and 0.5 Å were used for position z and distance r, respectively. Isoflurane motion in each pore conformation was evaluated every 0.1 ns from 100 ns simulations. Color indicates starting positions of isoflurane, 6′ (red) or 13′ (blue), in the MD simulations.

Mentions: Over the course of the MD simulations of the resting ELIC, isoflurane remained near the same two sites (6′ and 13′) as revealed in the crystal structure (Fig. 5a and Supplementary Fig. 4a). Although isoflurane at the 6′ site transiently migrated to the bottom of the pore at an early stage of the simulation, it quickly returned to the original position. Isoflurane movement perpendicular to the channel axis was largely confined within 2 Å of the pore radius in two replicated simulations (Fig. 5c and Supplementary Fig. 4a), indicating stable binding in the closed pore. In contrast, isoflurane molecules in the modeled desensitized pore moved away substantially from their initial positions (Fig. 5b,d and Supplementary Fig. 4b) and deviated from the center of the pore (Fig. 5d and Supplementary Fig. 4c). Although the modeled pore may not capture quantitative changes of ELIC in the transition from the resting to a desensitized conformation, it at least predicts how expansion at the upper half of the pore affects isoflurane binding.


Direct Pore Binding as a Mechanism for Isoflurane Inhibition of the Pentameric Ligand-gated Ion Channel ELIC.

Chen Q, Kinde MN, Arjunan P, Wells MM, Cohen AE, Xu Y, Tang P - Sci Rep (2015)

Isoflurane binding is more stable in the closed channel.Probabilities of finding an isoflurane molecule (center of mass) in molecular dynamics (MD) simulations at position z along the pore axis, P(z), and at the distance r from the pore axis, P(r), were calculated for (a,c) the closed channel and (b,d) a desensitized channel. A probability is defined as the ratio of the number of snapshots where isoflurane was found at the position z or at the distance r to the total snapshots chosen from the simulation. The bin widths of 1 Å and 0.5 Å were used for position z and distance r, respectively. Isoflurane motion in each pore conformation was evaluated every 0.1 ns from 100 ns simulations. Color indicates starting positions of isoflurane, 6′ (red) or 13′ (blue), in the MD simulations.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4561908&req=5

f5: Isoflurane binding is more stable in the closed channel.Probabilities of finding an isoflurane molecule (center of mass) in molecular dynamics (MD) simulations at position z along the pore axis, P(z), and at the distance r from the pore axis, P(r), were calculated for (a,c) the closed channel and (b,d) a desensitized channel. A probability is defined as the ratio of the number of snapshots where isoflurane was found at the position z or at the distance r to the total snapshots chosen from the simulation. The bin widths of 1 Å and 0.5 Å were used for position z and distance r, respectively. Isoflurane motion in each pore conformation was evaluated every 0.1 ns from 100 ns simulations. Color indicates starting positions of isoflurane, 6′ (red) or 13′ (blue), in the MD simulations.
Mentions: Over the course of the MD simulations of the resting ELIC, isoflurane remained near the same two sites (6′ and 13′) as revealed in the crystal structure (Fig. 5a and Supplementary Fig. 4a). Although isoflurane at the 6′ site transiently migrated to the bottom of the pore at an early stage of the simulation, it quickly returned to the original position. Isoflurane movement perpendicular to the channel axis was largely confined within 2 Å of the pore radius in two replicated simulations (Fig. 5c and Supplementary Fig. 4a), indicating stable binding in the closed pore. In contrast, isoflurane molecules in the modeled desensitized pore moved away substantially from their initial positions (Fig. 5b,d and Supplementary Fig. 4b) and deviated from the center of the pore (Fig. 5d and Supplementary Fig. 4c). Although the modeled pore may not capture quantitative changes of ELIC in the transition from the resting to a desensitized conformation, it at least predicts how expansion at the upper half of the pore affects isoflurane binding.

Bottom Line: Electrophysiology measurements with a single-point mutation at position 6' or 13' support the notion that binding at these sites renders isoflurane inhibition.Molecular dynamics simulations suggested that isoflurane binding was more stable in the resting than in a desensitized pore conformation.This study presents compelling evidence for a direct pore-binding mechanism of isoflurane inhibition, which has a general implication for inhibitory action of general anesthetics on pLGICs.

View Article: PubMed Central - PubMed

Affiliation: Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, 15260, USA.

ABSTRACT
Pentameric ligand-gated ion channels (pLGICs) are targets of general anesthetics, but molecular mechanisms underlying anesthetic action remain debatable. We found that ELIC, a pLGIC from Erwinia chrysanthemi, can be functionally inhibited by isoflurane and other anesthetics. Structures of ELIC co-crystallized with isoflurane in the absence or presence of an agonist revealed double isoflurane occupancies inside the pore near T237(6') and A244(13'). A pore-radius contraction near the extracellular entrance was observed upon isoflurane binding. Electrophysiology measurements with a single-point mutation at position 6' or 13' support the notion that binding at these sites renders isoflurane inhibition. Molecular dynamics simulations suggested that isoflurane binding was more stable in the resting than in a desensitized pore conformation. This study presents compelling evidence for a direct pore-binding mechanism of isoflurane inhibition, which has a general implication for inhibitory action of general anesthetics on pLGICs.

No MeSH data available.


Related in: MedlinePlus