Acetylcholine receptor subunit homomer formation requires compatibility between amino acid residues of the M 1 and M2 transmembrane segments

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Abstract
The neuronal nicotinic acetylcholine receptor (nAChR) subunits a3 and 0 have different assembly behavior when expressed in heterologous expression systems: α3 subunits require other subunits to assemble functional nAChRs, whereas α7 subunits can produce homomeric nAChRs. A previous analysis of α7 α3 chimeric constructs identified a domain comprising the first putative membrane-spanning segment, M1, as essential to homomeric assembly. The present study dissected further this domain, identifying three amino acid residues, which are located at the most intracellular third of the M1 transmembrane segment, as important in the assembly of homomers. Moreover, formation of homooligomeric complexes seems to require a compatible accommodation between this region and certain residues of the second transmembrane segment, M2. Thus, compatibility between defined domains of the M1 and M2 transmembrane segments appears as a determinant factor governing homomer association of nAChR subunits.