PUBLICATION
Ion access pathway to the transmembrane pore in P2X receptor channels
- Authors
- Kawate, T., Robertson, J.L., Li, M., Silberberg, S.D., and Swartz, K.J.
- ID
- ZDB-PUB-110609-28
- Date
- 2011
- Source
- The Journal of general physiology 137(6): 579-590 (Journal)
- Registered Authors
- Keywords
- none
- MeSH Terms
-
- Action Potentials
- Crystallization
- HEK293 Cells
- Humans
- Ion Channels
- Ion Transport/physiology*
- Mesylates
- Models, Molecular
- Mutagenesis
- Patch-Clamp Techniques
- Protein Conformation
- Receptors, Purinergic P2X/chemistry
- Receptors, Purinergic P2X/metabolism*
- PubMed
- 21624948 Full text @ J. Gen. Physiol.
Citation
Kawate, T., Robertson, J.L., Li, M., Silberberg, S.D., and Swartz, K.J. (2011) Ion access pathway to the transmembrane pore in P2X receptor channels. The Journal of general physiology. 137(6):579-590.
Abstract
P2X receptors are trimeric cation channels that open in response to the binding of adenosine triphosphate (ATP) to a large extracellular domain. The x-ray structure of the P2X4 receptor from zebrafish (zfP2X4) receptor reveals that the extracellular vestibule above the gate opens to the outside through lateral fenestrations, providing a potential pathway for ions to enter and exit the pore. The extracellular region also contains a void at the central axis, providing a second potential pathway. To investigate the energetics of each potential ion permeation pathway, we calculated the electrostatic free energy by solving the Poisson-Boltzmann equation along each of these pathways in the zfP2X4 crystal structure and a homology model of rat P2X2 (rP2X2). We found that the lateral fenestrations are energetically favorable for monovalent cations even in the closed-state structure, whereas the central pathway presents strong electrostatic barriers that would require structural rearrangements to allow for ion accessibility. To probe ion accessibility along these pathways in the rP2X2 receptor, we investigated the modification of introduced Cys residues by methanethiosulfonate (MTS) reagents and constrained structural changes by introducing disulfide bridges. Our results show that MTS reagents can permeate the lateral fenestrations, and that these become larger after ATP binding. Although relatively small MTS reagents can access residues in one of the vestibules within the central pathway, no reactive positions were identified in the upper region of this pathway, and disulfide bridges that constrain movements in that region do not prevent ion conduction. Collectively, these results suggest that ions access the pore using the lateral fenestrations, and that these breathe as the channel opens. The accessibility of ions to one of the chambers in the central pathway likely serves a regulatory function.
Genes / Markers
Expression
Phenotype
Mutations / Transgenics
Human Disease / Model
Sequence Targeting Reagents
Fish
Orthology
Engineered Foreign Genes
Mapping