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Mutations Causing Slow‐Channel Myasthenia Reveal That a Valine Ring in the Channel Pore of Muscle AChR is Optimized for Stabilizing Channel Gating
Author(s) -
Shen XinMing,
Okuno Tatsuya,
Milone Margherita,
Otsuka Kenji,
Takahashi Koji,
Komaki Hirofumi,
Giles Elizabeth,
Ohno Kinji,
Engel Andrew G.
Publication year - 2016
Publication title -
human mutation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 162
eISSN - 1098-1004
pISSN - 1059-7794
DOI - 10.1002/humu.23043
Subject(s) - valine , congenital myasthenic syndrome , leucine , biology , alanine , acetylcholine receptor , protein subunit , gating , mutation , amino acid , transmembrane domain , biophysics , glycine , biochemistry , receptor , gene
We identify two novel mutations in acetylcholine receptor (AChR) causing a slow‐channel congenital myasthenia syndrome (CMS) in three unrelated patients (Pts). Pt 1 harbors a heterozygous βV266A mutation (p.Val289Ala) in the second transmembrane domain (M2) of the AChR β subunit ( CHRNB1 ). Pts 2 and 3 carry the same mutation at an equivalent site in the ε subunit ( CHRNE ), εV265A (p.Val285Ala). The mutant residues are conserved across all AChR subunits of all species and are components of a valine ring in the channel pore, which is positioned four residues above the leucine ring. Both βV266A and εV265A reduce the amino acid size and lengthen the channel opening bursts by fourfold by enhancing gating efficiency by approximately 30‐fold. Substitution of alanine for valine at the corresponding position in the δ and α subunit prolongs the burst duration four‐ and eightfold, respectively. Replacing valine at ε codon 265 either by a still smaller glycine or by a larger leucine also lengthens the burst duration. Our analysis reveals that each valine in the valine ring contributes to channel kinetics equally, and the valine ring has been optimized in the course of evolution to govern channel gating.