GABRB3 mutation, G32R, associated with childhood absence epilepsy alters ?1?3?2L ?-aminobutyric acid type A (GABAA) receptor expression and channel gating.

ABSTRACT: A GABA(A) receptor ?3 subunit mutation, G32R, has been associated with childhood absence epilepsy. We evaluated the possibility that this mutation, which is located adjacent to the most N-terminal of three ?3 subunit N-glycosylation sites, might reduce GABAergic inhibition by increasing glycosylation of ?3 subunits. The mutation had three major effects on GABA(A) receptors. First, coexpression of ?3(G32R) subunits with ?1 or ?3 and ?2L subunits in HEK293T cells reduced surface expression of ?2L subunits and increased surface expression of ?3 subunits, suggesting a partial shift from ternary ??3?2L receptors to binary ??3 and homomeric ?3 receptors. Second, ?3(G32R) subunits were more likely than ?3 subunits to be N-glycosylated at Asn-33, but increases in glycosylation were not responsible for changes in subunit surface expression. Rather, both phenomena could be attributed to the presence of a basic residue at position 32. Finally, ?1?3(G32R)?2L receptors had significantly reduced macroscopic current density. This reduction could not be explained fully by changes in subunit expression levels (because ?2L levels decreased only slightly) or glycosylation (because reduction persisted in the absence of glycosylation at Asn-33). Single channel recording revealed that ?1?3(G32R)?2L receptors had impaired gating with shorter mean open time. Homology modeling indicated that the mutation altered salt bridges at subunit interfaces, including regions important for subunit oligomerization. Our results suggest both a mechanism for mutation-induced hyperexcitability and a novel role for the ?3 subunit N-terminal ?-helix in receptor assembly and gating.

SUBMITTER: Gurba KN 

PROVIDER: S-EPMC3320954 | biostudies-literature | 2012 Apr

REPOSITORIES: biostudies-literature