Gating-induced conformational rearrangement of the ?-aminobutyric acid type A receptor ?-? subunit interface in the membrane-spanning domain.

ABSTRACT: GABA(A) receptors mediate fast inhibitory synaptic transmission. The transmembrane ion channel is lined by a ring of five ? helices, M2 segments, one from each subunit. An outer ring of helices comprising the alternating M1, M3, and M4 segments from each subunit surrounds the inner ring and forms the interface with the lipid bilayer. The structural rearrangements that follow agonist binding and culminate in opening of the ion pore remain incompletely characterized. Propofol and other intravenous general anesthetics bind at the ?M3-?M1 subunit interface. We sought to determine whether this region undergoes conformational changes during GABA activation. We measured the reaction rate of p-chloromercuribenzenesulfonate (pCMBS) with cysteines substituted in the GABA(A) receptor ?1M1 and ?2M3 segments. In the presence of GABA, the pCMBS reaction rate increased significantly in a cluster of residues in the extracellular third of the ?1M1 segment facing the ?2M3 segment. Mutation of the ?2M2 segment 19' position, R269Q, altered the pCMBS reaction rate with several ?1M1 Cys, some only in the resting state and others only in the GABA-activated state. Thus, ?2R269 is charged in both states. GABA activation induced disulfide bond formation between ?2R269C and ?1I228C. The experiments demonstrate that ?1M1 moves in relationship to ?2M2R269 during gating. Thus, channel gating does not involve rigid body movements of the entire transmembrane domain. Channel gating causes changes in the relative position of transmembrane segments both within a single subunit and relative to the neighboring subunits.

SUBMITTER: Bali M 

PROVIDER: S-EPMC3431678 | biostudies-literature | 2012 Aug

REPOSITORIES: biostudies-literature