Primary structure of β subunit precursor of calf muscle acetylcholine receptor deduced from cDNA sequence

Abstract

Clones harbouring cDNA sequences for the β subunit precursor of the acetylcholine receptor from calf skeletal muscle have been isolated. Nucleotide sequence analysis of the cloned cDNA has disclosed the primary structure of this polypeptide, which consists of 505 amino acids including a hydrophobic prepeptide of 24 amino acids. The β subunit of the calf muscle acetylcholine receptor, like the α and γ subunits of the same receptor and the a subunit of its human counterpart, exhibits structural features common to all four subunits of the Torpedo electroplax receptor, apparently being oriented across the membrane in the same manner as proposed for the fish receptor subunits. The degree of sequence homology between the calf and Torpedoβ subunits (59%) is comparable to that between the γ subunits (56%), but is lower than that between the α subunits of the two species (81%). Some regions of the β subunit molecule, including the region corresponding to the putative acetylcholine binding area on the α subunit and the region encompassing the clustered putative transmembrane segments M1, M2 and M3, are relatively well conserved between the two species.