scholarly journals Ancestral acetylcholine receptor β-subunit forms homopentamers that prime before opening spontaneously

2022 ◽  
Author(s):  
Christian J.G. Tessier ◽  
R. Michel Sturgeon ◽  
Johnathon R. Emlaw ◽  
Gregory D. McCluskey ◽  
F. Javier Pérez-Areales ◽  
...  
Keyword(s):  
Ion Channels ◽  
Acetylcholine Receptor ◽  
Acetylcholine Receptors ◽  
Common Ancestor ◽  
Single Channel ◽  
Receptor Activity ◽  
Β Subunit ◽  
Receptor Function ◽  
Muscle Type ◽  
Α Subunits

Human adult muscle-type acetylcholine receptors are heteropentameric ion channels formed from two α-subunits, and one each of the β-, δ-, and ϵ- subunits. To form functional channels, the subunits must assemble with one another in a precise stoichiometry and arrangement. Despite being different, the four subunits share a common ancestor that is presumed to have formed homopentamers. The extent to which the properties of the modern-day receptor result from its subunit complexity is unknown. Here we show that a reconstructed ancestral muscle-type β-subunit can form homopentameric ion channels. These homopentamers open spontaneously and display single-channel hallmarks of muscle type acetylcholine receptor activity. Our findings demonstrate that signature features of muscle-type acetylcholine receptor function are independent of agonist, and do not necessitate the complex heteropentameric architecture of the modern-day receptor.

scholarly journals A single historical substitution drives an increase in acetylcholine receptor complexity

2021 ◽  
Vol 118 (7) ◽  
pp. e2018731118
Author(s):  
Johnathon R. Emlaw ◽  
Christian J. G. Tessier ◽  
Gregory D. McCluskey ◽  
Melissa S. McNulty ◽  
Yusuf Sheikh ◽  
...  
Keyword(s):  
Amino Acid ◽  
Acetylcholine Receptor ◽  
Amino Acid Substitution ◽  
Binding Sites ◽  
Acetylcholine Receptors ◽  
Single Channel ◽  
Single Amino Acid ◽  
Β Subunit ◽  
Subunit Stoichiometry ◽  
Sequence Reconstruction

Human adult muscle-type acetylcholine receptors are heteropentameric ion channels formed from four different, but evolutionarily related, subunits. These subunits assemble with a precise stoichiometry and arrangement such that two chemically distinct agonist-binding sites are formed between specific subunit pairs. How this subunit complexity evolved and became entrenched is unclear. Here we show that a single historical amino acid substitution is able to constrain the subunit stoichiometry of functional acetylcholine receptors. Using a combination of ancestral sequence reconstruction, single-channel electrophysiology, and concatenated subunits, we reveal that an ancestral β-subunit can not only replace the extant β-subunit but can also supplant the neighboring δ-subunit. By forward evolving the ancestral β-subunit with a single amino acid substitution, we restore the requirement for a δ-subunit for functional channels. These findings reveal that a single historical substitution necessitates an increase in acetylcholine receptor complexity and, more generally, that simple stepwise mutations can drive subunit entrenchment in this model heteromeric protein.

Disorders of the neuromuscular junction

2010 ◽  
pp. 5177-5184 ◽  
Author(s):  
David Hilton-Jones ◽  
Jacqueline Palace
Keyword(s):  
Ion Channels ◽  
Neuromuscular Junction ◽  
Acetylcholine Receptor ◽  
Acetylcholine Receptors ◽  
Muscle Receptor ◽  
Male Preponderance ◽  
Female Bias ◽  
Anti Acetylcholine

Two fundamentally different pathological processes are associated with disease at the neuromuscular junction: (1) acquired disorders in which autoantibodies are directed against nerve or muscle receptor or ion channels; (2) rare inherited conditions in which the defect may be pre- or postsynaptic. Aetiology and epidemiology—the fundamental disorder is loss of functional acetylcholine receptors most frequently as a result of binding of anti-acetylcholine receptor (anti-AChR) antibodies. Incidence is about 10 per million population and prevalence about 8 per 100 000, with a marked female bias in cases aged under 40 years and male preponderance in those over 50 years. Thymomas occur in about 10% of cases....

Molecular simulation studies of hydrophobic gating in nanopores and ion channels

2015 ◽  
Vol 43 (2) ◽  
pp. 146-150 ◽  
Author(s):  
Jemma L. Trick ◽  
Prafulla Aryal ◽  
Stephen J. Tucker ◽  
Mark S. P. Sansom
Keyword(s):  
Ion Channels ◽  
Simple Model ◽  
Acetylcholine Receptor ◽  
Nicotinic Acetylcholine Receptor ◽  
Single Channel ◽  
Experimental Studies ◽  
Physical Nature ◽  
Simulation Studies ◽  
Nicotinic Acetylcholine ◽  
Gating Mechanisms

Gating in channels and nanopores plays a key role in regulating flow of ions across membranes. Molecular simulations provide a ‘computational microscope’ which enables us to examine the physical nature of gating mechanisms at the level of the single channel molecule. Water enclosed within the confines of a nanoscale pore may exhibit unexpected behaviour. In particular, if the molecular surfaces lining the pore are hydrophobic this promotes de-wetting of the pore. De-wetting is observed as stochastic liquid–vapour transitions within a pore, and may lead to functional closure of a pore to the flow of ions and/or water. Such behaviour was first observed in simulations of simple model nanopores and referred to as ‘hydrophobic gating’. Simulations of both the nicotinic acetylcholine receptor and of TWIK-1 potassium channels (the latter alongside experimental studies) suggest hydrophobic gating may occur in some biological ion channels. Current studies are focused on designing hydrophobic gates into biomimetic nanopores.

scholarly journals Incorporation of acetylcholine receptors into liposomes. Vesicle structure and acetylcholine receptor function.

1982 ◽  
Vol 257 (12) ◽  
pp. 7122-7134 ◽  
Author(s):  
R Anholt ◽  
D R Fredkin ◽  
T Deerinck ◽  
M Ellisman ◽  
M Montal ◽  
...  
Keyword(s):  
Acetylcholine Receptor ◽  
Acetylcholine Receptors ◽  
Receptor Function

scholarly journals The mechanism of agrin-induced acetylcholine receptor aggregation

1991 ◽  
Vol 331 (1261) ◽  
pp. 273-280 ◽  
Keyword(s):  
Neuromuscular Junction ◽  
Tyrosine Phosphorylation ◽  
Acetylcholine Receptor ◽  
Acetylcholine Receptors ◽  
Neuromuscular Junctions ◽  
Electric Organ ◽  
Motor Axon ◽  
Β Subunit ◽  
Axon Terminals ◽  
Receptor Aggregation

Agrin, a protein isolated from the synapse-rich electric organ of Torpedo californica , induces the formation of specializations on myotubes in culture which resemble the post-synaptic apparatus at the vertebrate skeletal neuromuscular junction. For example, the specializations contain aggregates of acetylcholine receptors and acetylcholinesterase. This report summarizes the evidence that the formation of the postsynaptic apparatus at developing and regenerating neuromuscular junctions is triggered by the release of agrin from motor axon terminals and describes results of recent experiments which suggest that agrininduced tyrosine phosphorylation of the β subunit of the acetylcholine receptor may play a role in receptor aggregation.

The 5-hydroxytryptamine type 3 (5-HT3) receptor reveals a novel determinant of single-channel conductance

2004 ◽  
Vol 32 (3) ◽  
pp. 547-552 ◽  
Author(s):  
J.A. Peters ◽  
S.P. Kelley ◽  
J.I. Dunlop ◽  
E.F. Kirkness ◽  
T.G. Hales ◽  
...  
Keyword(s):  
Ion Channels ◽  
Acetylcholine Receptor ◽  
Nicotinic Acetylcholine Receptor ◽  
Single Channel ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Nicotinic Acetylcholine ◽  
Ultrastructural Studies ◽  
Arginine Residues ◽  
Type 3

5-HT3 (5-hydroxytryptamine type 3) receptors are cation-selective ion channels of the Cys-loop transmitter-gated ion channel superfamily. Two 5-HT3 receptor subunits, 5-HT3A and 5-HT3B, have been characterized in detail, although additional putative 5-HT3 subunit genes (HTR3C, HTR3D and HTR3E) have recently been reported. 5-HT3 receptors function as homopentameric assemblies of the 5-HT3 subunit, or heteropentamers of 5-HT3A and 5-HT3B subunits of unknown stoichiometry. The single-channel conductances of human recombinant homomeric and heteromeric 5-HT3 receptors are markedly different, being <1 and approx. 16 pS respectively. Paradoxically, from the results of studies performed on the closely related nicotinic acetylcholine receptor, the channel-lining M2 domain of the 5-HT3A subunit is predicted to enhance cation conduction, whereas that of the 5-HT3B subunit would not. The present study describes a novel determinant of single-channel conductance, outwith the M2 domain, which accounts for this anomaly. Utilizing a panel of chimaeric 5-HT3A and 5-HT3B subunits, a profound determinant of single-channel conductance was traced to a putative amphipathic helix (the ‘HA stretch’) within the large cytoplasmic loop of the receptor. Replacement of three arginine residues (R432, R436 and R440) unique to the HA stretch of the 5-HT3A subunit with the aligned residues (Q395, D399 and A403) of the 5-HT3B subunit increased the single-channel conductance 28-fold. Significantly, from ultrastructural studies of the Torpedo nicotinic acetylcholine receptor, the key residues may be components of narrow openings within the inner vestibule of the channel, located in the cytoplasm, which contribute to the permeation pathway. Our findings indicate an important and hitherto unappreciated function for the HA stretch in the Cys-loop family of transmitter-gated ion channels.

scholarly journals Peimine, an Anti-Inflammatory Compound from Chinese Herbal Extracts, Modulates Muscle-Type Nicotinic Receptors

2021 ◽  
Vol 22 (20) ◽  
pp. 11287
Author(s):  
Armando Alberola-Die ◽  
José Antonio Encinar ◽  
Raúl Cobo ◽  
Gregorio Fernández-Ballester ◽  
José Manuel González-Ros ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Ion Channels ◽  
Nicotinic Acetylcholine Receptors ◽  
Acetylcholine Receptors ◽  
Transmembrane Domain ◽  
Muscle Type ◽  
Functional Studies ◽  
Voltage Dependent ◽  
Neuronal Tissues ◽  
Anti Inflammatory

Fritillaria bulbs are used in Traditional Chinese Medicine to treat several illnesses. Peimine (Pm), an anti-inflammatory compound from Fritillaria, is known to inhibit some voltage-dependent ion channels and muscarinic receptors, but its interaction with ligand-gated ion channels remains unexplored. We have studied if Pm affects nicotinic acetylcholine receptors (nAChRs), since they play broad functional roles, both in the nervous system and non-neuronal tissues. Muscle-type nAChRs were incorporated to Xenopus oocytes and the action of Pm on the membrane currents elicited by ACh (IAChs) was assessed. Functional studies were combined with virtual docking and molecular dynamics assays. Co-application of ACh and Pm reversibly blocked IACh, with an IC50 in the low micromolar range. Pm inhibited nAChR by: (i) open-channel blockade, evidenced by the voltage-dependent inhibition of IAch, (ii) enhancement of nAChR desensitization, revealed by both an accelerated IACh decay and a decelerated IACh deactivation, and (iii) resting-nAChR blockade, deduced from the IACh inhibition elicited by Pm when applied before ACh superfusion. In good concordance, virtual docking and molecular dynamics assays demonstrated that Pm binds to different sites at the nAChR, mostly at the transmembrane domain. Thus, Pm from Fritillaria bulbs, considered therapeutic herbs, targets nAChRs with high affinity, which might account for its anti-inflammatory actions.

Ion channel proteins in mouse and human vestibular tissue

2005 ◽  
Vol 132 (6) ◽  
pp. 916-923 ◽  
Author(s):  
Karin Hotchkiss ◽  
Margaret Harvey ◽  
Mary Pacheco ◽  
Bernd Sokolowski
Keyword(s):  
Ion Channels ◽  
Ion Channel ◽  
Inner Ear ◽  
Potassium Ion ◽  
Β Subunit ◽  
Potassium Ion Channel ◽  
Channel Proteins ◽  
Ion Channel Proteins ◽  
Vestibular Endorgans ◽  
Α Subunits

BACKGROUND AND OBJECTIVE: Electrical activity in hair cells and neurons of the inner ear is necessary for the transduction and modulation of stimuli that impinge on the cochlea and vestibular endorgans of the inner ear. The underlying basis of this activity is pore-forming proteins in the membrane of excitable cells that allow the influx and efflux of various ions, including Na+, Ca2+, and K+, among others. These channels are critical to both electrical activity as well as the development of excitable cells because they may initiate long-term signals that are important in the maintenance and survival of these cells. We investigated the expression of several Shaker potassium ion channel proteins and an accessory β subunit in the vestibular endorgans of mouse and human. METHODS: Vestibular tissue consisting of cristae ampullares was harvested from adult and neonatal mice as well as from human subjects undergoing vestibular surgery. Western blot analysis and immunoprecipitation were used to identify the presence or absence, in mouse, of α subunits Kv1.2, Kv1.4, and Kv1.5 and of β subunit Kvβ1.1 in mouse. Coimmunoprecipitation was used to identify interactions between α and β subunits. Immunohistochemistry was used to localize Kv1.2 in mouse and human tissues. RESULTS: The presence of Kvα1.2 and Kvβ1.1 was confirmed in adult mouse crista ampullaris by Western blotting. Coimmunoprecipitation experiments showed that Kv1.2 and Kvβ1.1 interact in these tissues. Immunostaining localized Kv1.2 to regions within and extraneous to the sensory epithelium of mouse and human cristae ampullares. In comparison, Kv1.4 and Kv1.5 were not found in the crista ampullaris. CONCLUSIONS: We describe the presence, location, and interaction of various potassium ion channel α subunits and a β subunit. These data are initial descriptions of potassium ion channels in the mammalian vestibular system and begin to provide an understanding of the protein subunits that form ion channels of the mammalian inner ear. In addition, our data show that there are interactions that occur that may regulate the biophysical properties of these channels, thereby contributing to the diversity of channel function. This knowledge is critical to understanding the genes that encode these channels and finding cures for pathologies of hearing and balance. SIGNIFICANCE: We detail initial characteristics of potassium ion channel proteins including α subunits Kv1.2, Kv1.4, and Kv1.5 and β subunit Kvβ1.1 in mammalian vestibular tissue. This knowledge is critical to understanding the processing of vestibular stimuli and the regulation of endolymphatic function. Mutations of ion channels can cause neurological pathologies including auditory and vestibular disorders in humans.

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