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The startle disease mutation α1S270T predicts shortening of glycinergic synaptic currents

KEY POINTS: Loss‐of‐function mutations in proteins found at glycinergic synapses, most commonly in the α1 subunit of the glycine receptor (GlyR), cause the startle disease/hyperekplexia channelopathy in man. It was recently proposed that the receptors responsible are presynaptic homomeric GlyRs, rat...

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Autores principales: Wu, Zhiyi, Lape, Remigijus, Jopp‐Saile, Lea, O'Callaghan, Benjamin J., Greiner, Timo, Sivilotti, Lucia G.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: John Wiley and Sons Inc. 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7649747/
https://www.ncbi.nlm.nih.gov/pubmed/32445491
http://dx.doi.org/10.1113/JP279803
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author Wu, Zhiyi
Lape, Remigijus
Jopp‐Saile, Lea
O'Callaghan, Benjamin J.
Greiner, Timo
Sivilotti, Lucia G.
author_facet Wu, Zhiyi
Lape, Remigijus
Jopp‐Saile, Lea
O'Callaghan, Benjamin J.
Greiner, Timo
Sivilotti, Lucia G.
author_sort Wu, Zhiyi
collection PubMed
description KEY POINTS: Loss‐of‐function mutations in proteins found at glycinergic synapses, most commonly in the α1 subunit of the glycine receptor (GlyR), cause the startle disease/hyperekplexia channelopathy in man. It was recently proposed that the receptors responsible are presynaptic homomeric GlyRs, rather than postsynaptic heteromeric GlyRs (which mediate glycinergic synaptic transmission), because heteromeric GlyRs are less affected by many startle mutations than homomers. We examined the α1 startle mutation S270T, at the extracellular end of the M2 transmembrane helix. Recombinant heteromeric GlyRs were less impaired than homomers by this mutation when we measured their response to equilibrium applications of glycine. However, currents elicited by synaptic‐like millisecond applications of glycine to outside‐out patches were much shorter (7‐ to 10‐fold) in all mutant receptors, both homomeric and heteromeric. Thus, the synaptic function of heteromeric receptors is likely to be impaired by the mutation. ABSTRACT: Human startle disease is caused by mutations in glycine receptor (GlyR) subunits or in other proteins associated with glycinergic synapses. Many startle mutations are known, but it is hard to correlate the degree of impairment at molecular level with the severity of symptoms in patients. It was recently proposed that the disease is caused by disruption in the function of presynaptic homomeric GlyRs (rather than postsynaptic heteromeric GlyRs), because homomeric GlyRs are more sensitive to loss‐of‐function mutations than heteromers. Our patch‐clamp recordings from heterologously expressed GlyRs characterised in detail the functional consequences of the α1S270T startle mutation, which is located at the extracellular end of the pore lining M2 transmembrane segment (18ʹ). This mutation profoundly decreased the maximum single‐channel open probability of homomeric GlyRs (to 0.16; cf. 0.99 for wild type) but reduced only marginally that of heteromeric GlyRs (0.96; cf. 0.99 for wild type). However, both heteromeric and homomeric mutant GlyRs became less sensitive to the neurotransmitter glycine. Responses evoked by brief, quasi‐synaptic pulses of glycine onto outside‐out patches were impaired in mutant receptors, as deactivation was approximately 10‐ and 7‐fold faster for homomeric and heteromeric GlyRs, respectively. Our data suggest that the α1S270T mutation is likely to affect the opening step in GlyR activation. The faster decay of synaptic currents mediated by mutant heteromeric GlyRs is expected to reduce charge transfer at the synapse, despite the high equilibrium open probability of these mutant channels.
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spelling pubmed-76497472020-11-16 The startle disease mutation α1S270T predicts shortening of glycinergic synaptic currents Wu, Zhiyi Lape, Remigijus Jopp‐Saile, Lea O'Callaghan, Benjamin J. Greiner, Timo Sivilotti, Lucia G. J Physiol Molecular and Cellular KEY POINTS: Loss‐of‐function mutations in proteins found at glycinergic synapses, most commonly in the α1 subunit of the glycine receptor (GlyR), cause the startle disease/hyperekplexia channelopathy in man. It was recently proposed that the receptors responsible are presynaptic homomeric GlyRs, rather than postsynaptic heteromeric GlyRs (which mediate glycinergic synaptic transmission), because heteromeric GlyRs are less affected by many startle mutations than homomers. We examined the α1 startle mutation S270T, at the extracellular end of the M2 transmembrane helix. Recombinant heteromeric GlyRs were less impaired than homomers by this mutation when we measured their response to equilibrium applications of glycine. However, currents elicited by synaptic‐like millisecond applications of glycine to outside‐out patches were much shorter (7‐ to 10‐fold) in all mutant receptors, both homomeric and heteromeric. Thus, the synaptic function of heteromeric receptors is likely to be impaired by the mutation. ABSTRACT: Human startle disease is caused by mutations in glycine receptor (GlyR) subunits or in other proteins associated with glycinergic synapses. Many startle mutations are known, but it is hard to correlate the degree of impairment at molecular level with the severity of symptoms in patients. It was recently proposed that the disease is caused by disruption in the function of presynaptic homomeric GlyRs (rather than postsynaptic heteromeric GlyRs), because homomeric GlyRs are more sensitive to loss‐of‐function mutations than heteromers. Our patch‐clamp recordings from heterologously expressed GlyRs characterised in detail the functional consequences of the α1S270T startle mutation, which is located at the extracellular end of the pore lining M2 transmembrane segment (18ʹ). This mutation profoundly decreased the maximum single‐channel open probability of homomeric GlyRs (to 0.16; cf. 0.99 for wild type) but reduced only marginally that of heteromeric GlyRs (0.96; cf. 0.99 for wild type). However, both heteromeric and homomeric mutant GlyRs became less sensitive to the neurotransmitter glycine. Responses evoked by brief, quasi‐synaptic pulses of glycine onto outside‐out patches were impaired in mutant receptors, as deactivation was approximately 10‐ and 7‐fold faster for homomeric and heteromeric GlyRs, respectively. Our data suggest that the α1S270T mutation is likely to affect the opening step in GlyR activation. The faster decay of synaptic currents mediated by mutant heteromeric GlyRs is expected to reduce charge transfer at the synapse, despite the high equilibrium open probability of these mutant channels. John Wiley and Sons Inc. 2020-06-18 2020-08-15 /pmc/articles/PMC7649747/ /pubmed/32445491 http://dx.doi.org/10.1113/JP279803 Text en © 2020 The Authors. The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
spellingShingle Molecular and Cellular
Wu, Zhiyi
Lape, Remigijus
Jopp‐Saile, Lea
O'Callaghan, Benjamin J.
Greiner, Timo
Sivilotti, Lucia G.
The startle disease mutation α1S270T predicts shortening of glycinergic synaptic currents
title The startle disease mutation α1S270T predicts shortening of glycinergic synaptic currents
title_full The startle disease mutation α1S270T predicts shortening of glycinergic synaptic currents
title_fullStr The startle disease mutation α1S270T predicts shortening of glycinergic synaptic currents
title_full_unstemmed The startle disease mutation α1S270T predicts shortening of glycinergic synaptic currents
title_short The startle disease mutation α1S270T predicts shortening of glycinergic synaptic currents
title_sort startle disease mutation α1s270t predicts shortening of glycinergic synaptic currents
topic Molecular and Cellular
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7649747/
https://www.ncbi.nlm.nih.gov/pubmed/32445491
http://dx.doi.org/10.1113/JP279803
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