Effects of Disease-Associated Mutations on the Conformations of GABA(A) Receptors

Abstract

GABA(A) receptors are critical for proper transmission of inhibitory signals in the central nervous system, and are common targets of anesthetic and anxiolytic drugs. Several naturally occurring mutations in such receptors can cause an increased likelihood of seizures. In particular, gamma-K289M on the M2-M3 loop attached to the pore-lining M2 helices is associated with Generalized Epilepsy and Febrile Seizures. At the single channel level, the mutation dramatically reduces current amplitude in some subspecies, and increases deactivation rate in other subspecies. The molecular mechanism through which the mutation causes these effects is unknown. Using a homology model of the GABA(A) receptor based on the recently solved structure for the homologous glutamate-gated chloride channel (GluCl), we ran molecular dynamics simulations of multiple replicas incorporating both the Wild-type and the mutation, at room temperature and at temperatures inducing febrile seizures. We find distinct effects of temperature on the mutant for some conformational variables, including those governing the pore radius. From these results we propose a molecular mechanism for rapid but unstable closure of GABA(A) receptors, which would be likely to cause flickering in single channel recordings.