期刊
JOURNAL OF GENERAL PHYSIOLOGY
卷 116, 期 3, 页码 449-460出版社
ROCKEFELLER UNIV PRESS
DOI: 10.1085/jgp.116.3.449
关键词
congenital myasthenic syndrome; single channel kinetics; hidden Markov modeling; channel gating; energy landscape
类别
资金
- NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE [R37NS031744, R01NS031744, R56NS006277, R01NS006277] Funding Source: NIH RePORTER
- NINDS NIH HHS [R37 NS031744, NS6277, R01 NS031744, R56 NS006277, NS31744, R01 NS006277] Funding Source: Medline
- Wellcome Trust Funding Source: Medline
We describe the genetic and kinetic defects in a congenital myasthenic syndrome due to the mutation epsilon A411P in the amphipathic helix of the acetylcholine receptor (AChR) epsilon subunit. Myasthenic patients from three unrelated families are either homozygous for epsilon A411P or are heterozygous and harbor a null mutation in the second epsilon allele, indicating that epsilon A411P is recessive. We expressed human AChRs containing wild-type or A411P epsilon subunits in 293HEK cells, recorded single channel currents at high bandwidth, and determined microscopic rate constants for individual channels using hidden Markov modeling. For individual wild-type and mutant channels, each rate constant distributes as a Gaussian function, but the spread in the distributions for channel opening and closing rate constants is greatly expanded by epsilon A411P. Prolines engineered into positions flanking residue 411 of the epsilon subunit greatly increase the range of activation kinetics similar to epsilon A411P, whereas prolines engineered into positions equivalent to epsilon A411 in beta and delta subunits are without effect. Thus, the amphipathic helix of the epsilon subunit stabilizes the channel, minimizing the number and range of kinetic modes accessible to individual AChRs. The findings suggest that analogous stabilizing structures are present in other ion channels, and possibly allosteric proteins in general, and that they evolved to maintain uniformity of activation episodes. The findings further suggest that the fundamental gating mechanism of the AChR channel can be explained by a corrugated energy landscape superimposed on a steeply sloped energy well.
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