A conserved disulfide loop facilitates conformational maturation in the subunits of the acetylcholine receptor

• Published in: Brain research. Molecular brain research. Vol. 41; no. 1; pp. 289 - 300
• Main Authors: Walcott, Elisabeth C, Sumikawa, Katumi
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 05.09.1996; Elsevier
• Subjects: Acetylcholine receptor; Animals; Assembly signal; Binding Sites; Biological and medical sciences; Bungarotoxins - metabolism; Bungarotoxins - pharmacology; Cell receptors; Cell structures and functions; Disulfide loop; Disulfides - chemistry; Epitopes - immunology; Fundamental and applied biological sciences. Psychology; Molecular and cellular biology; Monoamines receptors (catecholamine, serotonine, histamine, acetylcholine); Mutagenesis, Site-Directed; Oocytes; Post-translational processing; Protein Conformation; Receptors, Cholinergic - chemistry; Receptors, Cholinergic - drug effects; Receptors, Cholinergic - genetics; Receptors, Cholinergic - immunology; Receptors, Cholinergic - metabolism; Recombinant Fusion Proteins - biosynthesis; RNA, Messenger - biosynthesis; Structure-Activity Relationship; Torpedo; Transfection; Xenopus laevis; α-Bungarotoxin; Disulfide loop; Assembly signal; α-Bungarotoxin; Acetylcholine receptor; Post-translational processing; Torpedo; Ripening; Posttranslational modification; Cholinergic receptor; Subunit; Conformation
• ISSN: 0169-328X; 1872-6941
• DOI: 10.1016/0169-328X(96)00122-2

To examine the structural determinants for the assembly of ligand-gated receptors, we constructed mutant α, β, γ and δ subunits of the Torpedo acetylcholine receptor (AChR), lacking one of the conserved cysteine residues which forms a 13-amino acid disulfide loop in the amino terminal domain of each subunit. Mutant subunits were co-expressed with complementary wild-type subunits in Xenopus oocytes. Using subunit-specific antisera and monoclonal antibodies that recognize the two distinct α-bungarotoxin (α-BuTX) sites on the AChR, we were able to distinguish immature subunit associations from conformationally mature AChR complexes. Removal of the disulfide loop on the α subunit completely destroyed the formation of the two toxin-binding sites, while removal of the structure on the β subunit had little effect. While mutant γ and δ subunits were capable of forming associations (immature assembly) with other subunits, the formation of α-BTX sites between α and mutant γ or mutant δ subunits was diminished. Interestingly, assembly of αβγ subunits remained efficient in the presence of mutant δ subunits, whereas assembly of αβδ subunits was inefficient in the presence of mutant γ subunits. Thus, these results indicate that the formation of the disulfide loop facilitates the conformational maturation of αγ and αδ complexes, which may be conditional for correct subunit coupling in assembling receptors. Furthermore, it seems likely that the correct coupling between the α and γ subunits is the most important step in subunit assembly.