Primary structure and functional expression of the α‐, β‐, γ‐, δ‐ and ɛ‐subunits of the acetylcholine receptor from rat muscle

Abstract

The isolation and characterization of five clones carrying sequences of the alpha-, beta-, gamma-, delta- and epsilon-subunit precursors of the rat muscle acetylcholine receptor (AChR) are described. The deduced amino acid sequences indicate that these polypeptides contain 457-519 amino acids and reveal the structural characteristics common to subunits of ligand-gated ion channels. The pattern of subunit-specific mRNA levels in rat muscle shows characteristic changes during development and following denervation, suggesting that innervation of muscle reduces the expression of the alpha-, beta- and delta-subunit mRNAs, suppresses the expression of the gamma-subunit mRNA, and induces expression of epsilon-subunit mRNA. Subunit-specific cRNAs generated in vitro were injected into Xenopus laevis oocytes, resulting in the assembly of two functionally different AChR channel subtypes. The AChR gamma, composed of the alpha-, beta-, gamma- and delta-subunits, has functional properties similar to those of the native AChRs in fetal muscle. The AChR epsilon, composed of alpha-, beta-, delta- and epsilon-subunits, corresponds to the end-plate channel of the adult muscle. Thus in rat skeletal muscle the motor nerve regulates the expression of two functionally different AChR subtypes with different molecular composition by the differential expression of subunit-specific mRNAs.

Elementary Steps in Synaptic Transmission Revealed by Currents Through Single Ion Channels

“…Both the amplitude of single channel currents recorded from oocytes and their average duration (Fig. 6C) were similar to elementary currents observed in bovine or rat skeletal muscle Witzemann et al, 1987;Witzemann et al, 1990). Thus, it seems that native channel isoforms reflect differences in subunit composition of the channel, in the case of AChR channel an exchange between the γ-and ε-subunit is the molecular difference between the two channel subtypes (Fig.…”

“…This differential regulation depends on differences in the regulatory sequences of the γ− and ε-subunit genes and their different responsiveness to neural and myogenic factors (Witzemann et al, 1990;Numberger et al, 1991;. Since in most cells, including neurones, channel isoforms are expressed which often are colocalized in a mosaic-like manner, the regulation of the abundance of channel isoforms by differential expression of subunit genes may be one mechanism by which long-term ('plastic') changes in chemical and electrical excitability can occur , for review).…”

Characterisation, crystallisation and preliminary X‐ray diffraction analysis of a Fab fragment of a rat monoclonal antibody with very high affinity for the human muscle acetylcholine receptor

“…Therefore, the reduced affinity of mAb192 for rat AChR should be due to differences within the c1 subunit and not to conformational constraints imposed by the other rat subunits. There are only two residues in the extracellular parts of the AChR CL subunit (residues ~~-209, 268-292 and 428437) in which the rat ~1 subunit differs from both the human and mouse a subunits [17,18]. These are residues 23 (Glu -+ Gly) and 195 (Asp, Thr+Asn).…”

Two adjacent E box elements and a M‐CAT box are involved in the muscle‐specific regulation of the rat acetylcholine receptor β subunit gene

“…The library was screened by plaque filter hybridization procedure with a 3zP-labelled AChR P subunit full-length cDNA clone [35] ; five positive clones were further classified by hybridization with a 19-bp oligonucleotide corresponding to the sequence 66-85 bp of the P coding region. One phage harbours the gene encoding the AChR P subunit and 1.8 kb of the 5' flanking region.…”