Membrane tethering enables an extracellular domain of the acetylcholine receptor alpha subunit to form a heterodimeric ligand-binding site
Wang, Z.Z.; Hardy, S.F.; Hall, Z.W.
Journal of Cell Biology 135(3): 809-817
1996
ISSN/ISBN: 0021-9525
PMID: 8909552
DOI: 10.1083/jcb.135.3.809
Accession: 009009272
The first step of assembly of the nicotinic acetylcholine receptor (AChR) of adult skeletal muscle is the specific association of the alpha subunit with either delta or epsilon subunits to form a heterodimer with a ligand-binding site. Previous experiments have suggested that heterodimer formation in the ER arises from interaction between the luminal, NH-2-terminal domains of the subunits. When expressed in COS cells with the delta subunit, however, the truncated NH-2-terminal domain of the alpha subunit folded correctly but did not form a heterodimer. Association with the delta subunit occurred only when the NH-2-terminal domain was retained in the ER and was tethered to the membrane by its own M1 transmembrane domain, by the transmembrane domain of another protein, or by a glycolipid link. In each case, the ligand-binding sites of the resulting heterodimers were indistinguishable from that formed when the full-length alpha subunit was used. Attachment to the membrane may promote interaction by concentrating or orienting the subunit; alternatively, a membrane-bound factor may facilitate subunit association.