Biochemical identification of the binding domain in the GABA(A) receptor-associated protein (GABARAP) mediating dimer formation.

The gamma-aminobutyric acid receptor type A (GABA(A)) receptor-associated protein (GABARAP) is a member of a growing family of intracellular membrane trafficking and/or fusion proteins and has been implicated in plasma membrane targeting and clustering of GABA(A) receptors. GABARAP interacts with microtubules and the gamma2 subunit of GABA(A) receptor and modulates channel kinetics. From crystal structures of GABARAP in high salt concentration it has been proposed that oligomerization of GABARAP might take place in a head-to-tail fashion. In this study, we report that GABARAP self-associates and dimerizes in physiological salt concentrations. We find no evidence for higher order complex larger than a dimer. By using deletion constructs of GABARAP we show that interaction takes place between amino acid 36 and 68. We further narrow the interacting domain by inhibiting the self-association, by adding GABARAP-derived synthetic peptides in GST pull-down assays and shows that the interaction specifically takes place in the previously identified GABARAP-GABA(A) receptor interaction domain from amino acid 41-51. The identification of binding domains in GABARAP allows for the study of GABARAP functions, including GABA(A) receptor dynamics.