Pentameric concatenated (α4)2(β2)3 and (α4)3(β2)2 nicotinic acetylcholine receptors: subunit arrangement determines functional expression

• Published in: British journal of pharmacology Vol. 156; no. 6; pp. 970 - 981
• Main Authors: Carbone, A‐L, Moroni, M, Groot‐Kormelink, P‐J, Bermudez, I
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.03.2009; Nature Publishing Group
• Subjects: Biological and medical sciences; concatenated receptors; Medical sciences; nicotinic acetylcholine receptors; Pharmacology. Drug treatments; Research Papers; Xenopus; Cholinergic receptor; concatenated receptors; Pentamer; Subunit; nicotinic acetylcholine receptors; Nicotinic receptor; Biological receptor
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.2008.00104.x

Background and purpose:  α4 and β2 nicotinic acetylcholine (ACh) receptor subunits expressed heterologously in Xenopus oocytes assemble into a mixed population of (α4)2(β2)3 and (α4)3(β2)2 receptors. In order to express these receptors separately in heterologous systems, we have engineered pentameric concatenated (α4)2(β2)3 and (α4)3(β2)2 receptors. Experimental approach:  α4 and β2 subunits were concatenated by synthetic linkers into pentameric constructs to produce either (α4)2(β2)3 or (α4)3(β2)2 receptors. Using two‐electrode voltage‐clamp techniques, we examined the ability of the concatenated constructs to produce functional expression in Xenopus oocytes. Functional constructs were further characterized in respect to agonists, competitive antagonists, Ca2+ permeability, sensitivity to modulation by Zn2+ and sensitivity to up‐regulation by chaperone protein 14‐3‐3. Key results:  We found that pentameric concatamers with a subunit arrangement of β2_α4_β2_α4_β2 or β2_α4_β2_α4_α4 were stable and functional in Xenopus oocytes. By comparison, when α4 and β2 were concatenated with a subunit order of β2_β2_α4_β2_α4 or β2_α4_α4_β2_α4, functional expression in Xenopus oocytes was very low, even though the proteins were synthesized and stable. Both β2_α4_β2_α4_β2 and β2_α4_β2_α4_α4 concatamers recapitulated the ACh concentration response curve, the sensitivity to Zn2+ modulation, Ca2+ permeability and the sensitivity to up‐regulation by chaperone protein 14‐3‐3 of the corresponding non‐linked (α4)2(β2)3 and (α4)3(β2)2 receptors respectively. Using these concatamers, we found that most α4β2‐preferring compounds studied, including A85380, 5I‐A85380, cytisine, epibatidine, TC2559 and dihydro‐β‐erythroidine, demonstrate stoichiometry‐specific potencies and efficacies. Conclusions and implications:  We concluded that the α4β2 nicotinic ACh receptors produced with β2_α4_β2_α4_β2 or β2_α4_β2_α4_α4 pentameric constructs are valid models of non‐linked (α4)2(β2)3 and (α4)3(β2)2 receptors respectively.