Assembly of nicotinic alpha7 subunits in Xenopus oocytes is partially blocked at the tetramer level.
The assembly of nicotinic alpha1beta1gammadelta, alpha3beta4, and alpha7 receptors and 5-hydroxytryptamine 3A (5HT3A) receptors was comparatively evaluated in Xenopus oocytes by blue native PAGE analysis. While alpha1betagammadelta subunits, alpha3beta4 subunits, and 5HT3A subunits combined efficiently to pentamers, alpha7 subunits existed in various assembly states including trimers, tetramers, pentamers, and aggregates. Only alpha7 subunits that completed the assembly process to homopentamers acquired complex-type carbohydrates and appeared at the cell surface. We conclude that Xenopus oocytes have a limited capacity to guide the assembly of alpha7 subunits, but not 5HT3A subunits to homopentamers. Accordingly, ER retention of imperfectly assembled alpha7 subunits rather than inefficient routing of fully assembled alpha7 receptors to the cell surface limits surface expression levels of alpha7 nicotinic acetylcholine receptors.
Nicke
Annette
A
Department of Molecular Pharmacology, Medical School of the Technical University of Aachen, Wendlingweg 2, D-52074 Aachen, Germany.
Thurau
Heike
H
Sadtler
Sven
S
Rettinger
Jürgen
J
Schmalzing
Günther
G
D000818:Animals; D006031:Glycosylation; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011134:Polysaccharides / Q000737:chemistry; D011499:Protein Processing, Post-Translational; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D044406:Receptors, Serotonin, 5-HT3 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis; D064569:alpha7 Nicotinic Acetylcholine Receptor
C579165:Chrna7 protein, rat; D011134:Polysaccharides; D021122:Protein Subunits; D011978:Receptors, Nicotinic; D044406:Receptors, Serotonin, 5-HT3; D064569:alpha7 Nicotinic Acetylcholine Receptor