Mutations of cytosolic loop residues impair assembly and maturation of alpha7 nicotinic acetylcholine receptors.

Mechanisms that regulate early events in the biogenesis of the alpha7 nicotinic acetylcholine receptor (alpha7 AChR) are not well understood. Data presented here show that single amino acid mutations in the cytoplasmic loop of the alpha7 AChR, between position 335 and 343, abolish or attenuate expression of mature pentameric alpha7 AChRs in both human embryonic kidney tsA201 (HEK) and neuronal SH-SY5Y cells. Although the number of mature alpha7 AChRs is increased significantly in the presence of the chaperone protein resistant to inhibitors of cholineesterase-3 in HEK cells, sucrose gradient sedimentation reveals that the vast majority of alpha7 subunits are aggregated or improperly assembled. Transfection of alpha7 AChRs in SH-SY5Y cells, which endogenously express the alpha7 AChR, results in a much larger fraction of subunits assembled into mature AChRs. Thus, efficient assembly of alpha7 AChRs is influenced by several regions of the large cytoplasmic domain, as well perhaps by other parts of its structure, and requires as yet unknown factors not required by other AChR subtypes.