Metabolic Stabilization of Muscle Nicotinic Acetylcholine Receptor by Rapsyn

Wang, Zuo-Zhong; Mathias, Askale; Gautam, Medha; Hall, Zach W.

doi:10.1523/jneurosci.19-06-01998.1999

Cited by 42 publications

(34 citation statements)

References 71 publications

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“…The β subunit has been chemically cross-linked to rapsyn in Torpedo membranes (33), and the association with rapsyn metabolically stabilizes the receptor by reducing its turnover at the EP (34). Our results show that the deletion mutations in the β subunit reduce cell surface more than total cellular expression, indicating that this region of the subunit may contribute to receptor turnover as well as to subunit oligomerization.…”

Section: Discussionmentioning

confidence: 76%

Mutation causing congenital myasthenia reveals acetylcholine receptor β/δ subunit interaction essential for assembly

Quiram¹,

Ohno²,

Milone³

et al. 1999

J. Clin. Invest.

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The protein sequence of ion channels governs not only their ultimate function, but also encodes instructions for their correct assembly. Converting the linear peptide into the mature protein requires correct folding, posttranslational modification, and, for most ion channels, oligomerization (1). For the acetylcholine receptor (AChR) at the motor endplate (EP), these steps likely depend on local sequences in many parts of its α, β, ε, and δ subunits. Identifying such key assembly sequences typically relies on mutating residues conserved across the AChR superfamily. However, by identifying the genetic defects underlying a congenital myasthenic syndrome (CMS), the present work reveals a region of the AChR β subunit essential for assembly.The amino-terminal, extracellular half of each AChR subunit is widely recognized to mediate its initial association leading to the assembled pentamer (2, 3). A cystine loop within the extracellular domain, formed between C128 and C142 in all AChR subunits, has drawn considerable attention regarding its role in contributing to assembly. Formation of cystine loops in both α and β subunits is required for specific conformational changes and subunit oligomerization steps at intermediate stages of assembly (4). Furthermore, specific residues preceding the cystine loop affect assembly efficiency (5), whereas residues following the loop govern subunit specificity of oligomerization (6). On the other hand, residues in the M1 and M2 transmembrane domains are essential for assembly of homomeric versus heteromeric AChRs (7).We now uncover an additional domain essential for AChR assembly by identifying and characterizing the molecular defects that cause a severe CMS associated with marked EP-AChR deficiency. The deficiency arises from 2 heteroallelic recessive mutations in the β subunit. One causes skipping of exon 8, which abolishes expression of pentameric AChR; the second is a 3-codon deletion (β426delEQE) in the long cytoplasmic loop between transmembrane domains M3 and M4, which severely curtails expression of cell-surface AChR. By coexpressing β426delEQE and related deletion mutants with combinations of wild-type subunits, we demonstrate that β426delEQE impairs AChR assembly by disrupting a specific interaction between β and δ subunits. MethodsMuscle specimens. Intercostal muscle specimens were obtained intact from origin to insertion from the patient and control subjects without muscle disease undergoing thoracic surgery. A limb-muscle specimen was obtained from the patient's mother. All human studies were in accord with the guidelines of the Institutional Review Board of the Mayo Clinic.AChR and acetylcholinesterase (AChE) were localized in cryostat sections by 2-color fluorescence (8). EPs were localized for electron microscopy (9) and quantitatively analyzed (10) We 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 exo...

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Section: Discussionmentioning

confidence: 76%

Mutation causing congenital myasthenia reveals acetylcholine receptor β/δ subunit interaction essential for assembly

Quiram¹,

Ohno²,

Milone³

et al. 1999

J. Clin. Invest.

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“…There is a wealth of studies showing a direct correlation between the amount of rapsyn present at NMJs and the abundance or the metabolic stability of synaptic AChRs (Brockhausen et al, 2008;Gervasio et al, 2007;Gervasio and Phillips, 2005;Luo et al, 2008;Martinez-Martinez et al, 2009;Wang et al, 1999). Furthermore, mutations in the RAPSN gene are amongst the most frequent causes for myasthenic syndromes, which are characterised by activity-dependent muscle weakness (Beeson et al, 2008;Müller et al, 2007).…”

Section: Discussionmentioning

confidence: 99%

Rapsyn mediates subsynaptic anchoring of PKA type I and stabilisation of acetylcholine receptor in vivo

Choi

Berrera

Reischl

et al. 2012

Journal of Cell Science

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SummaryThe stabilisation of acetylcholine receptors (AChRs) at the neuromuscular junction depends on muscle activity and the cooperative action of myosin Va and protein kinase A (PKA) type I. To execute its function, PKA has to be present in a subsynaptic microdomain where it is enriched by anchoring proteins. Here, we show that the AChR-associated protein, rapsyn, interacts with PKA type I in C2C12 and T-REx293 cells as well as in live mouse muscle beneath the neuromuscular junction. Molecular modelling, immunoprecipitation and bimolecular fluorescence complementation approaches identify an a-helical stretch of rapsyn to be crucial for binding to the dimerisation and docking domain of PKA type I. When expressed in live mouse muscle, a peptide encompassing the rapsyn a-helical sequence efficiently delocalises PKA type I from the neuromuscular junction. The same peptide, as well as a rapsyn construct lacking the a-helical domain, induces severe alteration of acetylcholine receptor turnover as well as fragmentation of synapses. This shows that rapsyn anchors PKA type I in close proximity to the postsynaptic membrane and suggests that this function is essential for synapse maintenance.

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“…This protein is thought to slow the metabolic degradation of the AChR (46,47) and function downstream of the Agrin/MuSK signaling, leading to AChR clustering (48). Recently, we found that Rapsyn stabilizes AChR clusters by interacting with calpain, a calcium-dependent protease involved in ACh-induced dispersion of AChR clusters (8).…”

Section: Discussionmentioning

confidence: 99%

Wnt/β-Catenin Signaling Suppresses Rapsyn Expression and Inhibits Acetylcholine Receptor Clustering at the Neuromuscular Junction

Wang

Ruan

Qian

et al. 2008

Journal of Biological Chemistry

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Metabolic Stabilization of Muscle Nicotinic Acetylcholine Receptor by Rapsyn

Cited by 42 publications

References 71 publications

Mutation causing congenital myasthenia reveals acetylcholine receptor β/δ subunit interaction essential for assembly

Mutation causing congenital myasthenia reveals acetylcholine receptor β/δ subunit interaction essential for assembly

Rapsyn mediates subsynaptic anchoring of PKA type I and stabilisation of acetylcholine receptor in vivo

Wnt/β-Catenin Signaling Suppresses Rapsyn Expression and Inhibits Acetylcholine Receptor Clustering at the Neuromuscular Junction

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