Polly A. Quiram, Kinji Ohno, Margherita Milone, Marc C. Patterson, Ned J. Pruitt, Joan M. Brengman, Steven M. Sine, Andrew G. Engel
J Clin Invest.
1999;
104(10):1403–1410
doi:10.1172/JCI8179
This article Copyright © 1999, The American Society for Clinical Investigation
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e describe a severe postsynaptic congenital myasthenic syndrome with marked endplate acetylcholine receptor (AChR) deficiency caused by 2 heteroallelic mutations in the β subunit gene. One mutation causes skipping of exon 8, truncating the β subunit before its M1 transmembrane domain, and abolishing surface expression of pentameric AChR. The other mutation, a 3-codon deletion (β426delEQE) in the long cytoplasmic loop between the M3 and M4 domains, curtails but does not abolish expression. By coexpressing β426delEQE with combinations of wild-type subunits in 293 HEK cells, we demonstrate that β426delEQE impairs AChR assembly by disrupting a specific interaction between β and δ subunits. Studies with related deletion and missense mutants indicate that secondary structure in this region of the β subunit is crucial for interaction with the δ subunit. The findings imply that the mutated residues are positioned at the interface between β and δ subunits and demonstrate contribution of this local region of the long cytoplasmic loop to AChR assembly.J. Clin. Invest. 104:1403–1410 (1999).
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