scholarly journals Cryo-EM structure of the mechanically activated ion channel OSCA1.2

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Sebastian Jojoa-Cruz ◽  
Kei Saotome ◽  
Swetha E Murthy ◽  
Che Chun Alex Tsui ◽  
Mark SP Sansom ◽  
...  
Keyword(s):  
Ion Channels ◽  
Turgor Pressure ◽  
Ion Permeation ◽  
Membrane Tension ◽  
Transmembrane Helices ◽  
Channel Conductance ◽  
Cryo Electron Microscopy ◽  
Stress Sensing ◽  
Dynamics Simulations

Mechanically activated ion channels underlie touch, hearing, shear-stress sensing, and response to turgor pressure. OSCA/TMEM63s are a newly-identified family of eukaryotic mechanically activated ion channels opened by membrane tension. The structural underpinnings of OSCA/TMEM63 function are not explored. Here, we elucidate high resolution cryo-electron microscopy structures of OSCA1.2, revealing a dimeric architecture containing eleven transmembrane helices per subunit and surprising topological similarities to TMEM16 proteins. We locate the ion permeation pathway within each subunit by demonstrating that a conserved acidic residue is a determinant of channel conductance. Molecular dynamics simulations reveal membrane interactions, suggesting the role of lipids in OSCA1.2 gating. These results lay a foundation to decipher how the structural organization of OSCA/TMEM63 is suited for their roles as MA ion channels.

scholarly journals Conserved His-Gly motif of acid-sensing ion channels resides in a reentrant ‘loop’ implicated in gating and ion selectivity

2020 ◽  
Author(s):  
Nate Yoder ◽  
Eric Gouaux
Keyword(s):  
Ion Channels ◽  
Ion Selectivity ◽  
Fear Memory ◽  
Amino Terminus ◽  
Ion Permeation ◽  
Structural Explanation ◽  
Cryo Electron Microscopy ◽  
Acid Sensing Ion Channels ◽  
And Function

ABSTRACTAcid-sensing ion channels (ASICs) are proton-gated members of the epithelial sodium channel/degenerin (ENaC/DEG) superfamily of ion channels and are expressed throughout central and peripheral nervous systems. The homotrimeric splice variant ASIC1a has been implicated in nociception, fear memory, mood disorders and ischemia. Here we extract full-length chicken ASIC1a (cASIC1a) from cell membranes using styrene maleic acid (SMA) copolymer, yielding structures of ASIC1a channels in both high pH resting and low pH desensitized conformations by single-particle cryo-electron microscopy (cryo-EM). The structures of resting and desensitized channels reveal a reentrant loop at the amino terminus of ASIC1a that includes the highly conserved ‘His-Gly’ (HG) motif. The reentrant loop lines the lower ion permeation pathway and buttresses the ‘Gly-Ala-Ser’ (GAS) constriction, thus providing a structural explanation for the role of the His-Gly dipeptide in the structure and function of ASICs.

scholarly journals The His-Gly motif of acid-sensing ion channels resides in a reentrant ‘loop’ implicated in gating and ion selectivity

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Nate Yoder ◽  
Eric Gouaux
Keyword(s):  
Ion Channels ◽  
Ion Selectivity ◽  
Fear Memory ◽  
Amino Terminus ◽  
Ion Permeation ◽  
Structural Explanation ◽  
Cryo Electron Microscopy ◽  
Acid Sensing Ion Channels ◽  
And Function

Acid-sensing ion channels (ASICs) are proton-gated members of the epithelial sodium channel/degenerin (ENaC/DEG) superfamily of ion channels and are expressed throughout the central and peripheral nervous systems. The homotrimeric splice variant ASIC1a has been implicated in nociception, fear memory, mood disorders and ischemia. Here, we extract full-length chicken ASIC1 (cASIC1) from cell membranes using styrene maleic acid (SMA) copolymer, elucidating structures of ASIC1 channels in both high pH resting and low pH desensitized conformations by single-particle cryo-electron microscopy (cryo-EM). The structures of resting and desensitized channels reveal a reentrant loop at the amino terminus of ASIC1 that includes the highly conserved ‘His-Gly’ (HG) motif. The reentrant loop lines the lower ion permeation pathway and buttresses the ‘Gly-Ala-Ser’ (GAS) constriction, thus providing a structural explanation for the role of the His-Gly dipeptide in the structure and function of ASICs.

scholarly journals Structural and Functional Insights into the Role of Guard Cell Ion Channels in Abiotic Stress-Induced Stomatal Closure

Plants ◽  
2021 ◽  
Vol 10 (12) ◽  
pp. 2774
Author(s):  
Hamdy Kashtoh ◽  
Kwang-Hyun Baek
Keyword(s):  
Ion Channels ◽  
Guard Cell ◽  
Stomatal Closure ◽  
Turgor Pressure ◽  
Anion Channel ◽  
Weather Conditions ◽  
Guard Cells ◽  
Water Transpiration ◽  
Structure And Functions

A stomatal pore is formed by a pair of specialized guard cells and serves as a major gateway for water transpiration and atmospheric CO2 influx for photosynthesis in plants. These pores must be tightly controlled, as inadequate CO2 intake and excessive water loss are devastating for plants. When the plants are exposed to extreme weather conditions such as high CO2 levels, O3, low air humidity, and drought, the turgor pressure of the guard cells exhibits an appropriate response against these stresses, which leads to stomatal closure. This phenomenon involves a complex network of ion channels and their regulation. It is well-established that the turgor pressure of guard cells is regulated by ions transportation across the membrane, such as anions and potassium ions. In this review, the guard cell ion channels are discussed, highlighting the structure and functions of key ion channels; the SLAC1 anion channel and KAT1 potassium channel, and their regulatory components, emphasizing their significance in guard cell response to various stimuli.

scholarly journals Structure and assembly of calcium homeostasis modulator proteins

2019 ◽  
Author(s):  
Johanna L Syrjanen ◽  
Kevin Michalski ◽  
Tsung-Han Chou ◽  
Timothy Grant ◽  
Shanlin Rao ◽  
...  
Keyword(s):  
Calcium Homeostasis ◽  
Neuronal Excitability ◽  
Dependent Manner ◽  
Transmembrane Helices ◽  
Cryo Electron Microscopy ◽  
Large Pore ◽  
Oligomeric Assembly ◽  
Voltage Dependent ◽  
Bona Fide ◽  
Dynamics Simulations

AbstractBiological membranes of many tissues and organs contain large-pore channels designed to permeate a wide variety of ions and metabolites. Examples include connexin, innexin, and pannexin, which form gap junctions and/or bona fide cell surface channels. The most recently identified large-pore channels are the calcium homeostasis modulators (CALHMs), which permeate ions and ATP in a voltage-dependent manner to control neuronal excitability, taste signaling, and pathologies of depression and Alzheimer’s disease. Despite such critical biological roles, the structures and patterns of oligomeric assembly remain unclear. Here, we reveal the first structures of two CALHMs, CALHM1 and CALHM2, by single particle cryo-electron microscopy, which show novel assembly of the four transmembrane helices into channels of 8-mers and 11-mers, respectively. Furthermore, molecular dynamics simulations suggest that lipids can favorably assemble into a bilayer within the larger CALHM2 pore, but not within CALHM1, demonstrating the potential correlation between pore-size, lipid accommodation, and channel activity.

scholarly journals The SERCA residue Glu340 mediates inter-domain communication that guides Ca2+ transport

2020 ◽  
Author(s):  
Maxwell M. G. Geurts ◽  
Johannes D. Clausen ◽  
Bertrand Arnou ◽  
Cedric Montigny ◽  
Guillaume Lenoir ◽  
...  
Keyword(s):  
Atp Hydrolysis ◽  
Transmembrane Helices ◽  
Tight Coupling ◽  
Hydrogen Bonding Pattern ◽  
Plasmic Reticulum ◽  
Cytosolic Domains ◽  
Dynamics Simulations ◽  
P Type ◽  
Intramolecular Communication

AbstractThe sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) is a P-type ATPase that transports Ca2+ from the cytosol into the SR/ER lumen, driven by ATP. This primary transport activity depends on tight coupling between movements of the transmembrane helices forming the two Ca2+ binding sites and of the cytosolic headpiece mediating ATP hydrolysis. We have addressed the molecular basis for this intramolecular communication by analyzing the structure and functional properties of the SERCA mutant E340A. The mutated Glu340 residue is strictly conserved among the P-type ATPase family of membrane transporters and is located at a seemingly strategic position at the interface between the phosphorylation domain and the cytosolic ends of five out of SERCA’s ten transmembrane helices. The mutant displays a marked slowing of the Ca2+-binding kinetics, and its crystal structure in the presence of Ca2+ and ATP analogue reveals a rotated headpiece, altered connectivity between the cytosolic domains and altered hydrogen bonding pattern around residue 340. Supported by molecular dynamics simulations, we conclude that the E340A mutation causes a stabilization of the Ca2+ sites in a more occluded state, hence displaying slowed dynamics. This finding underpins a crucial role of Glu340 in inter-domain communication between the headpiece and the Ca2+-binding transmembrane region.

scholarly journals Determinants of ion selectivity in ASIC1a- and ASIC2a-containing acid-sensing ion channels

2020 ◽  
Vol 152 (2) ◽  
Author(s):  
Timothy Lynagh ◽  
Emelie Flood ◽  
Céline Boiteux ◽  
Zeshan Pervez Sheikh ◽  
Toby W. Allen ◽  
...  
Keyword(s):  
Ion Channels ◽  
Essential Role ◽  
Ion Selectivity ◽  
Site Directed Mutagenesis ◽  
Ion Permeation ◽  
Extracellular Acidification ◽  
Acid Sensing Ion Channels ◽  
Molecular Determinants ◽  
Energy Simulations

Trimeric acid-sensing ion channels (ASICs) contribute to neuronal signaling by converting extracellular acidification into excitatory sodium currents. Previous work with homomeric ASIC1a implicates conserved leucine (L7′) and consecutive glycine-alanine-serine (GAS belt) residues near the middle, and conserved negatively charged (E18′) residues at the bottom of the pore in ion permeation and/or selectivity. However, a conserved mechanism of ion selectivity throughout the ASIC family has not been established. We therefore explored the molecular determinants of ion selectivity in heteromeric ASIC1a/ASIC2a and homomeric ASIC2a channels using site-directed mutagenesis, electrophysiology, and molecular dynamics free energy simulations. Similar to ASIC1a, E18′ residues create an energetic preference for sodium ions at the lower end of the pore in ASIC2a-containing channels. However, and in contrast to ASIC1a homomers, ion permeation through ASIC2a-containing channels is not determined by L7′ side chains in the upper part of the channel. This may be, in part, due to ASIC2a-specific negatively charged residues (E59 and E62) that lower the energy of ions in the upper pore, thus making the GAS belt more important for selectivity. This is confirmed by experiments showing that the L7′A mutation has no effect in ASIC2a, in contrast to ASIC1a, where it eliminated selectivity. ASIC2a triple mutants eliminating both L7′ and upper charges did not lead to large changes in selectivity, suggesting a different role for L7′ in ASIC2a compared with ASIC1a channels. In contrast, we observed measurable changes in ion selectivity in ASIC2a-containing channels with GAS belt mutations. Our results suggest that ion conduction and selectivity in the upper part of the ASIC pore may differ between subtypes, whereas the essential role of E18′ in ion selectivity is conserved. Furthermore, we demonstrate that heteromeric channels containing mutations in only one of two ASIC subtypes provide a means of functionally testing mutations that render homomeric channels nonfunctional.

The Role of Hydrophobicity in the Stability and pH-Switchability of (RXDX)4 and Coumarin-RXDX Conjugate β-Sheets

2020 ◽  
Author(s):  
Ryan Weber ◽  
Martin McCullagh
Keyword(s):  
Biological Imaging ◽  
Ph Sensing ◽  
Hydrophobic Residue ◽  
Ideal Candidate ◽  
Self Assembling ◽  
Sensing Applications ◽  
Β Sheets ◽  
The Stability ◽  
Dynamics Simulations

<p>pH-switchable, self-assembling materials are of interest in biological imaging and sensing applications. Here we propose that combining the pH-switchability of RXDX (X=Ala, Val, Leu, Ile, Phe) peptides and the optical properties of coumarin creates an ideal candidate for these materials. This suggestion is tested with a thorough set of all-atom molecular dynamics simulations. We first investigate the dependence of pH-switchabiliy on the identity of the hydrophobic residue, X, in the bare (RXDX)<sub>4</sub> systems. Increasing the hydrophobicity stabilizes the fiber which, in turn, reduces the pH-switchabilty of the system. This behavior is found to be somewhat transferable to systems in which a single hydrophobic residue is replaced with a coumarin containing amino acid. In this case, conjugates with X=Ala are found to be unstable and both pHs while conjugates with X=Val, Leu, Ile and Phe are found to form stable β-sheets at least at neutral pH. The (RFDF)<sub>4</sub>-coumarin conjugate is found to have the largest relative entropy value of 0.884 +/- 0.001 between neutral and acidic coumarin ordering distributions. Thus, we posit that coumarin-(RFDF)<sub>4</sub> containing peptide sequences are ideal candidates for pH-sensing bioelectronic materials.</p>

Acid-Sensing Ion Channels

2020 ◽  
Author(s):  
Stefan Gründer
Keyword(s):  
Nervous System ◽  
Ion Channels ◽  
Excitatory Synapses ◽  
Detailed Characterization ◽  
High Affinity ◽  
Acid Sensing Ion Channels ◽  
Long Time ◽  
Pathological Pain

Acid-sensing ion channels (ASICs) are proton-gated Na+ channels. Being almost ubiquitously present in neurons of the vertebrate nervous system, their precise function remained obscure for a long time. Various animal toxins that bind to ASICs with high affinity and specificity have been tremendously helpful in uncovering the role of ASICs. We now know that they contribute to synaptic transmission at excitatory synapses as well as to sensing metabolic acidosis and nociception. Moreover, detailed characterization of mouse models uncovered an unanticipated role of ASICs in disorders of the nervous system like stroke, multiple sclerosis, and pathological pain. This review provides an overview on the expression, structure, and pharmacology of ASICs plus a summary of what is known and what is still unknown about their physiological functions and their roles in diseases.

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