A threonine residue in the M2 region of the beta1 subunit is needed for expression of functional alpha1beta1 GABA(A) receptors.
Although there is a high degree of homology in the M2 transmembrane segments of alpha1 and beta1 subunits, subunit-specific effects were observed in alpha1beta1 GABA(A) receptors expressed in Spodoptera frugipedra (Sf9) cells when the conserved 13' threonine residue in the M2 transmembrane region was mutated to alanine. When threonine 263 (13') was mutated to alanine in the beta1 subunit, high-affinity muscimol binding and the response to GABA were abolished. This did not occur when the threonine 263 (13') was mutated to alanine in the alpha1 subunit, but the rate of desensitisation increased and the effect of bicuculline, a competitive inhibitor, was reduced. The results show differential effects of subunits on receptor function and support a role for M2 in desensitisation.
Dalziel
J E
JE
Membrane Biology Program, John Curtin School of Medical Research, Australian National University, Canberra, ACT. julie.dalziel@anu.edu.au
Birnir
B
B
Everitt
A B
AB
Tierney
M L
ML
Cox
G B
GB
Gage
P W
PW
D000200:Action Potentials; D000409:Alanine / Q000235:genetics*; D000818:Animals; D002462:Cell Membrane / Q000737:chemistry; D005786:Gene Expression Regulation; D006801:Humans; D066298:In Vitro Techniques; D009118:Muscimol / Q000378:metabolism; D009154:Mutation; D011485:Protein Binding; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism*; D018080:Receptors, GABA-B / Q000235:genetics / Q000378:metabolism*; D018411:Spodoptera / Q000502:physiology; D013912:Threonine / Q000737:chemistry*
D011963:Receptors, GABA-A; D018080:Receptors, GABA-B; D009118:Muscimol; D013912:Threonine; D000409:Alanine