Mutations that impair the expression and/or function of gamma-aminobutyric acid type A (GABA(A)) receptors can lead to epilepsy. The familial epilepsy gamma 2(K289M) mutation affects a basic residue conserved in the TM2-3 linker of most GABA(A) subunits. We investigated the effect on expression and function of the Lys -> Met mutation in mouse alpha 1(K278M), beta 2(K274M), and gamma 2( K289M) subunits. Compared with cells expressing wild-type and alpha 1 beta 2 gamma 2(K289M) receptors, cells expressing alpha 1(K278M)beta 2 gamma 2 and alpha 1 beta 2(K274M)gamma 2 receptors exhibited reduced agonist-evoked current density and reduced GABA potency, with no change in single channel conductance. The low current density of alpha 1 beta 2(K274M)gamma 2 receptors coincided with reduced surface expression. By contrast the surface expression of alpha 1(K278M)beta 2 gamma 2 receptors was similar to wild-type and alpha 1 beta 2 gamma 2(K289M) receptors suggesting that the alpha 1(K278M) impairs function. In keeping with this interpretation GABA-activated channels mediated by alpha 1(K278M)gamma 2 receptors had brief open times. To a lesser extent gamma 2(K289M) also reduced mean open time, whereas beta 2(K274M) had no effect. We used propofol as an alternative GABA(A) receptor agonist to test whether the functional deficits of mutant subunits were specific to GABA activation. Propofol was less potent as an activator of alpha 1(K278M)beta 2 gamma 2 receptors. By contrast, neither beta 2(K274M) nor gamma 2(K289M) affected the potency of propofol. The beta 2(K274M) construct was unique in that it reduced the efficacy of propofol activation relative to GABA. These data suggest that the alpha 1 subunit Lys-278 residue plays a pivotal role in channel gating that is not dependent on occupancy of the GABA binding site. Moreover, the conserved TM2-3 loop lysine has an asymmetric function in different GABAA subunits.