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.
N1 - Publisher Copyright:
© 2014 American Academy of Neurology.
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.
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U2 - 10.1212/WNL.0000000000001079
DO - 10.1212/WNL.0000000000001079
M3 - Article
C2 - 25381298
AN - SCOPUS:84924120978
SN - 0028-3878
VL - 83
SP - 2247
EP - 2255
JO - Neurology
JF - Neurology
IS - 24
ER -