Regions of beta 4.beta 2 subunit chimeras that contribute to the agonist selectivity of neuronal nicotinic receptors.

Fifteen chimeric nicotinic receptor beta subunits were constructed consisting of N-terminal neuronal beta 4 sequences and C-terminal beta 2 sequences. Responses to cytisine, nicotine, or tetramethylammonium were compared to acetylcholine responses for these subunits expressed in Xenopus oocytes with alpha 3 subunits. The results show that (i) two residues in the extracellular domain of chimeric beta 4.beta 2 subunits (108 beta 2F/beta 4V, 110 beta 2S/beta 4T) account for much of the relative cytisine sensitivity; and (ii) four extracellular residues of chimeric beta 4.beta 2 subunits (112 beta 2A/beta 4V, 113 beta 2V/beta 4I and 115 beta 2S/beta 4R, 116 beta 2Y/beta 4S) account for most of the relative tetramethylammonium sensitivity. The data did not permit localization of nicotine sensitivity to any particular region.