Acetylcholine Receptor Channel Structure Probed in Cysteine-Substitution Mutants

TLDR

In the closed nicotinic acetylcholine receptor, side chains of alternate residues Ser248, Leu250, Ser252, and Thr254 in the M2 α‑subunit are exposed. The study aimed to identify channel‑lining residues to elucidate the structural bases of ion conduction, selectivity, and gating in the nicotinic acetylcholine receptor. Mutagenesis and covalent modification were combined to map residues lining the channel. The results indicate that residues α248–254 form a β strand with the gate nearer the cytoplasmic end, Leu251 becomes exposed upon opening, and these observations revise the model of closed and open channel structures.

Abstract

In order to understand the structural bases of ion conduction, ion selectivity, and gating in the nicotinic acetylcholine receptor, mutagenesis and covalent modification were combined to identify the amino acid residues that line the channel. The side chains of alternate residues—Ser248, Leu250, Ser252, and Thr254—in M2, a membrane-spanning segment of the α subunit, are exposed in the closed channel. Thus α 248-254 probably forms a β strand, and the gate is closer to the cytoplasmic end of the channel than any of these residues. On channel opening, Leu251 is also exposed. These results lead to a revised view of the closed and open channel structures.