ACETYLCHOLINE-RECEPTOR ASSEMBLY - SUBUNIT FOLDING AND OLIGOMERIZATIONOCCUR SEQUENTIALLY

The temperature sensitivity of nicotinic acetylcholine receptors (AChR s) from T. californica was used to identify steps in AChR subunit fold ing and oligomerization. Assembly intermediates were isolated by lower ing to an assembly-permissive temperature. The earliest identifiable a ssembly intermediates, alphabetagamma trimers, form minutes after subu nit synthesis. Alphabetagammadelta tetramers are formed slowly by the addition of delta subunits to trimers, and finally a second alpha subu nit is added to form alpha2betagammadelta pentamers. Between these oli gomerization steps, subunits fold as monitored by alpha-bungarotoxin-b inding site formation, appearance of antigenic epitopes, changes in ap parent molecular weight, and changes in detergent solubility. Subunit folding requires specific combinations of subunits and correlates in t ime with subunit additions, suggesting that these subunit folding even ts contribute to subunit recognition site formation during assembly.