The role of heterogeneity of intersubunit interfaces in the outer membrane leaflet in maintaining GABAA receptor activity.

GABA type A receptors (GABAAR) mediate fast inhibition processes in the CNS. We proposed that β2 Arg269 (19′) residue maintains the activated state of GABAAR by wedging its bulky side chain into β(+)/α(–) transmembrane interfaces in the outer membrane leaflet. To explore this hypothesis, we used the cryo-EM structure (6X3Z) of agonist-bound α1β2γ2 GABAAR and molecular dynamics. We found that the Arg19′ side chain tends to adopt a horizontal conformation at β(+)/α(–) interfaces, in which it forms strong contacts with both interface sides, thereby wedging the interfaces. We found that due to the presence of the γ subunit, two β(+)/α(−) interfaces are not identical in terms of the Arg19′ side chain dynamics. At other interfaces, the Arg19′ side chain adopts a vertical conformation in which it forms strong contacts only with residues from the principal subunit. We identified residues 15′, 20′, and 29′ of the principal subunits responsible for this difference in the Arg19′ side chain dynamics. We constructed models of mutant GABAAR in which the Arg19′ side chain dynamics in the two above interface groups are opposite to those of wild-type receptor. In this work, we proposed a new molecular mechanism for maintaining GABAAR in the activation state.