Structure of GABARAP in two conformations: implications for GABA(A) receptor localization and tubulin binding

GABARAP recognizes and binds the gamma2 subunit of the GABA(A) receptor, interacts with microtubules and the N-ethyl maleimide sensitive factor, and is proposed to function in GABA(A) receptor trafficking and postsynaptic localization. We have determined the crystal structure of human GABARAP at 1.6 A resolution. The structure comprises an N-terminal helical subdomain and a ubiquitin-like C-terminal domain. Structure-based mutational analysis demonstrates that the N-terminal subdomain is responsible for tubulin binding while the C-terminal domain contains the binding site for the GABA(A). A second GABARAP crystal form was determined at 1.9 A resolution and documents that GABARAP can self-associate in a head-to-tail manner. The structural details of this oligomerization reveal how GABARAP can both promote tubulin polymerization and facilitate GABA(A) receptor clustering.