Methionine 286 in transmembrane domain 3 of the GABAA receptor β subunit controls a binding cavity for propofol and other alkylphenol general anesthetics

gamma-Aminobutyric acid type A (GABA(A)) receptors are an important target for general anesthetic, in the central nervous system. Site-directed mutagenesis techniques have identified amino acid residues that are important for the positive modulation of GABA(A) receptors by general anesthetics. In the present study, we investigate the role oh an amino acid residue in transmembrane (TM) domain 3 of the GABA(A) receptor beta(2) subunit for modulation by the general anesthetic 2,6-diisopropylphenyl (propofol). Mutation of methionine 286 to tryptophan (M286W) in the beta(2) subunit abolished potentiation of GABA responses by propofol but did not affect direct receptor activation by propofol in the absence of GABA. In contrast, substitution of methionine 286 by alanine, cysteine, glutamate, lysine, phenylalanine, serine, or tyrosine was permissive for potentiation of GABA responses and direct activation by propofol. Using propofol analogs of varying molecular size, we shoe that the beta(2)(M286W) mutation resulted in a decrease in the 'cut-off' volume for propofol analog molecules to enhance GABA responses at GABA(A) alpha(1)beta(2)gamma(2), receptors. This suggests that mutation of M286 in the GABA(A) beta(2) subunit alters the dimensions oh a 'binding pocket' for propofol and related alkylphenol general anesthetics. (C) 2001 Published by Elsevier Science Ltd.