Membrane topology of the Drosophila vesicular glutamate transporter.
The vesicular glutamate transporters (VGLUTs) are responsible for packaging glutamate into synaptic vesicles, and are part of a family of structurally related proteins that mediate organic anion transport. Standard computer-based predictions of transmembrane domains have led to divergent topological models, indicating the need for experimentally derived predictions. Here we present data on the topology of the VGLUT ortholog from Drosophila melanogaster (DVGLUT). Using immunofluorescence assays of DVGLUT transiently localized to the plasma membrane of heterologously transfected cells, we have determined the accessibility of epitope tags inserted into the lumenal/extracellular face of the protein. Using immunoisolation, we have identified complementary tagged sites that face the cytoplasm. Our data show that DVGLUT contains 10 hydrophobic regions that completely span the membrane (TMs 1-10) and that the amino and carboxyl termini are cytosolic. Importantly, between TMs 4 and 5 is an unforeseen cytosolic loop of some 50 residues. Other domains exposed to the cytosol include loops between TMs 6-7 and 8-9, and regions C-terminal to TM2 and N-terminal to TM3. Between TM2 and 3 is a potentially hydrophobic, but topologically ambiguous region. Lumenal domains include sequences between TMs 1-2, 3-4, 5-6, 7-8 and 9-10. These data provide a basis for determining structure-function relationships for DVGLUT and other related proteins.
Fei
Hao
H
Department of Psychiatry and Biobehavioral Sciences, The David Geffen School of Medicine at UCLA, Gonda (Goldschmied) Center for Genetic and Neuroscience Research, Los Angeles, CA 90095-1761, USA.
Karnezis
Tara
T
Reimer
Richard J
RJ
Krantz
David E
DE
D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000737:chemistry*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D050496:Vesicular Glutamate Transport Proteins / Q000737:chemistry*
D050496:Vesicular Glutamate Transport Proteins