Mutations causing congenital myasthenia reveal principal coupling pathway in the acetylcholine receptor ?-subunit

PubMed: 293674592-s2.0-85051235382We identify 2 homozygous mutations in the ?-subunit of the muscle acetylcholine receptor (AChR) in 3 patients with severe congenital myasthenia: ?R218W in the pre-M1 region in 2 patients and ?E184K in the ?8-?9 linker in 1 patient. Arg218 is conserved in all eukaryotic members of the Cys-loop receptor superfamily, while Glu184 is conserved in the ?-, ?-, and ?-subunits of AChRs from all species. ?R218W reduces channel gating efficiency 338-fold and AChR expression on the cell surface 5-fold, whereas ?E184K reduces channel gating efficiency 11-fold but does not alter AChR cell surface expression. Determinations of the effective channel gating rate constants, combined with mutant cycle analyses, demonstrate strong energetic coupling between ?R218 and ?E184, and between ?R218 and ?E45 from the ?1-?2 linker, as also observed for equivalent residues in the principal coupling pathway of the ?-subunit. Thus, efficient and rapid gating of the AChR channel is achieved not only by coupling between conserved residues within the principal coupling pathway of the ?-subunit, but also between corresponding residues in the ?-subunit.National Institute of Neurological Disorders and Stroke, NINDS: R01NS006277, R01NS03174