Mutant SNAP25B causes myasthenia, cortical hyperexcitability, ataxia, and intellectual disability

Xin Ming Shen, Duygu Selcen, Joan Brengman, Andrew G Engel

Research output: Contribution to journalArticle

57 Citations (Scopus)

Abstract

Objective: To identify and characterize the molecular basis of a syndrome associated with myasthenia, cortical hyperexcitability, cerebellar ataxia, and intellectual disability. Methods: We performed in vitro microelectrode studies of neuromuscular transmission, performed exome and Sanger sequencing, and analyzed functional consequences of the identified mutation in expression studies. Results: Neuromuscular transmission at patient endplates was compromised by reduced evoked quantal release. Exome sequencing identified a dominant de novo variant, p.Ile67Asn, in SNAP25B, a SNARE protein essential for exocytosis of synaptic vesicles from nerve terminals and of dense-core vesicles from endocrine cells. Ca2+-triggered exocytosis is initiated when synaptobrevin attached to synaptic vesicles (v-SNARE) assembles with SNAP25B and syntaxin anchored in the presynaptic membrane (t-SNAREs) into an a-helical coiled-coil held together by hydrophobic interactions. Pathogenicity of the Ile67Asn mutation was confirmed by 2 measures. First, the Ca21 triggered fusion of liposomes incorporating v-SNARE with liposomes containing t-SNAREs was hindered when t-SNAREs harbored the mutant SNAP25B moiety. Second, depolarization of bovine chromaffin cells transfected with mutant SNAP25B or with mutant plus wildtype SNAP25B markedly reduced depolarization-evoked exocytosis compared with wild-type transfected cells. Conclusion: Ile67Asn variant in SNAP25B is pathogenic because it inhibits synaptic vesicle exocytosis. We attribute the deleterious effects of the mutation to disruption of the hydrophobic a-helical coiled-coil structure of the SNARE complex by replacement of a highly hydrophobic isoleucine by a strongly hydrophilic asparagine.

Original languageEnglish (US)
Pages (from-to)2247-2255
Number of pages9
JournalNeurology
Volume83
Issue number24
StatePublished - Dec 1 2014

Fingerprint

SNARE Proteins
Ataxia
Intellectual Disability
Exocytosis
Synaptic Vesicles
Exome
Liposomes
Mutation
R-SNARE Proteins
Qa-SNARE Proteins
Cerebellar Ataxia
Chromaffin Cells
Endocrine Cells
Isoleucine
Asparagine
Secretory Vesicles
Microelectrodes
Hydrophobic and Hydrophilic Interactions
Virulence
Membranes

ASJC Scopus subject areas

  • Clinical Neurology

Cite this

Mutant SNAP25B causes myasthenia, cortical hyperexcitability, ataxia, and intellectual disability. / Shen, Xin Ming; Selcen, Duygu; Brengman, Joan; Engel, Andrew G.

In: Neurology, Vol. 83, No. 24, 01.12.2014, p. 2247-2255.

Research output: Contribution to journalArticle

@article{374b9652c8c0434f9eaa37eed53c333b,
title = "Mutant SNAP25B causes myasthenia, cortical hyperexcitability, ataxia, and intellectual disability",
abstract = "Objective: To identify and characterize the molecular basis of a syndrome associated with myasthenia, cortical hyperexcitability, cerebellar ataxia, and intellectual disability. Methods: We performed in vitro microelectrode studies of neuromuscular transmission, performed exome and Sanger sequencing, and analyzed functional consequences of the identified mutation in expression studies. Results: Neuromuscular transmission at patient endplates was compromised by reduced evoked quantal release. Exome sequencing identified a dominant de novo variant, p.Ile67Asn, in SNAP25B, a SNARE protein essential for exocytosis of synaptic vesicles from nerve terminals and of dense-core vesicles from endocrine cells. Ca2+-triggered exocytosis is initiated when synaptobrevin attached to synaptic vesicles (v-SNARE) assembles with SNAP25B and syntaxin anchored in the presynaptic membrane (t-SNAREs) into an a-helical coiled-coil held together by hydrophobic interactions. Pathogenicity of the Ile67Asn mutation was confirmed by 2 measures. First, the Ca21 triggered fusion of liposomes incorporating v-SNARE with liposomes containing t-SNAREs was hindered when t-SNAREs harbored the mutant SNAP25B moiety. Second, depolarization of bovine chromaffin cells transfected with mutant SNAP25B or with mutant plus wildtype SNAP25B markedly reduced depolarization-evoked exocytosis compared with wild-type transfected cells. Conclusion: Ile67Asn variant in SNAP25B is pathogenic because it inhibits synaptic vesicle exocytosis. We attribute the deleterious effects of the mutation to disruption of the hydrophobic a-helical coiled-coil structure of the SNARE complex by replacement of a highly hydrophobic isoleucine by a strongly hydrophilic asparagine.",
author = "Shen, {Xin Ming} and Duygu Selcen and Joan Brengman and Engel, {Andrew G}",
year = "2014",
month = "12",
day = "1",
language = "English (US)",
volume = "83",
pages = "2247--2255",
journal = "Neurology",
issn = "0028-3878",
publisher = "Lippincott Williams and Wilkins",
number = "24",

}

TY - JOUR

T1 - Mutant SNAP25B causes myasthenia, cortical hyperexcitability, ataxia, and intellectual disability

AU - Shen, Xin Ming

AU - Selcen, Duygu

AU - Brengman, Joan

AU - Engel, Andrew G

PY - 2014/12/1

Y1 - 2014/12/1

N2 - Objective: To identify and characterize the molecular basis of a syndrome associated with myasthenia, cortical hyperexcitability, cerebellar ataxia, and intellectual disability. Methods: We performed in vitro microelectrode studies of neuromuscular transmission, performed exome and Sanger sequencing, and analyzed functional consequences of the identified mutation in expression studies. Results: Neuromuscular transmission at patient endplates was compromised by reduced evoked quantal release. Exome sequencing identified a dominant de novo variant, p.Ile67Asn, in SNAP25B, a SNARE protein essential for exocytosis of synaptic vesicles from nerve terminals and of dense-core vesicles from endocrine cells. Ca2+-triggered exocytosis is initiated when synaptobrevin attached to synaptic vesicles (v-SNARE) assembles with SNAP25B and syntaxin anchored in the presynaptic membrane (t-SNAREs) into an a-helical coiled-coil held together by hydrophobic interactions. Pathogenicity of the Ile67Asn mutation was confirmed by 2 measures. First, the Ca21 triggered fusion of liposomes incorporating v-SNARE with liposomes containing t-SNAREs was hindered when t-SNAREs harbored the mutant SNAP25B moiety. Second, depolarization of bovine chromaffin cells transfected with mutant SNAP25B or with mutant plus wildtype SNAP25B markedly reduced depolarization-evoked exocytosis compared with wild-type transfected cells. Conclusion: Ile67Asn variant in SNAP25B is pathogenic because it inhibits synaptic vesicle exocytosis. We attribute the deleterious effects of the mutation to disruption of the hydrophobic a-helical coiled-coil structure of the SNARE complex by replacement of a highly hydrophobic isoleucine by a strongly hydrophilic asparagine.

AB - Objective: To identify and characterize the molecular basis of a syndrome associated with myasthenia, cortical hyperexcitability, cerebellar ataxia, and intellectual disability. Methods: We performed in vitro microelectrode studies of neuromuscular transmission, performed exome and Sanger sequencing, and analyzed functional consequences of the identified mutation in expression studies. Results: Neuromuscular transmission at patient endplates was compromised by reduced evoked quantal release. Exome sequencing identified a dominant de novo variant, p.Ile67Asn, in SNAP25B, a SNARE protein essential for exocytosis of synaptic vesicles from nerve terminals and of dense-core vesicles from endocrine cells. Ca2+-triggered exocytosis is initiated when synaptobrevin attached to synaptic vesicles (v-SNARE) assembles with SNAP25B and syntaxin anchored in the presynaptic membrane (t-SNAREs) into an a-helical coiled-coil held together by hydrophobic interactions. Pathogenicity of the Ile67Asn mutation was confirmed by 2 measures. First, the Ca21 triggered fusion of liposomes incorporating v-SNARE with liposomes containing t-SNAREs was hindered when t-SNAREs harbored the mutant SNAP25B moiety. Second, depolarization of bovine chromaffin cells transfected with mutant SNAP25B or with mutant plus wildtype SNAP25B markedly reduced depolarization-evoked exocytosis compared with wild-type transfected cells. Conclusion: Ile67Asn variant in SNAP25B is pathogenic because it inhibits synaptic vesicle exocytosis. We attribute the deleterious effects of the mutation to disruption of the hydrophobic a-helical coiled-coil structure of the SNARE complex by replacement of a highly hydrophobic isoleucine by a strongly hydrophilic asparagine.

UR - http://www.scopus.com/inward/record.url?scp=84924120978&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84924120978&partnerID=8YFLogxK

M3 - Article

VL - 83

SP - 2247

EP - 2255

JO - Neurology

JF - Neurology

SN - 0028-3878

IS - 24

ER -