Modulation of the neuronal glutamate transporter EAAT4 by two interacting proteins

Glutamate is the main excitatory neurotransmitter in the mammalian central nervous system and is removed from the synaptic cleft by sodium-dependent g lutamate transporters. To date, five distinct glutamate transporters have b een cloned from animal and human tissue: GLAST (EAAT1), GLT-1 (EAAT2), EAAC 1 (EAAT3), EAAT4, and EAAT5 (refs 1-5). GLAST and GLT-1 are localized prima rily in astrocytes(6,7), whereas EAAC1 (refs 8, 9), EAAT4 (refs 9-11) and E AAT5 (ref. 5) are neuronal. Studies of EAAT4 and EAAC1 indicate an extrasyn aptic localization on perisynaptic membranes that are near release sites(8- 10). This localization facilitates rapid glutamate binding, and may have a role in shaping the amplitude of postsynaptic responses in densely packed c erebellar terminals(12-15). We have used a yeast two-hybrid screen to ident ify interacting proteins that may be involved in regulating EAAT4- the glut amate transporter expressed predominately in the cerebellum-or in targeting and/or anchoring or clustering the transporter to the target site. Here we report the identification and characterization of two proteins, GTRAP41 an d GTRAP48 (for glutamate transporter EAAT4 associated protein) that specifi cally interact with the intracellular carboxy-terminal domain of EAAT4 and modulate its glutamate transport activity.