title: BRAG1, a Sec7 domain-containing protein, is a component of the postsynaptic density of excitatory synapses.
abstract: The postsynaptic density (PSD) at excitatory synapses is a dynamic complex of glutamatergic receptors and associated proteins that governs synaptic structure and coordinates signal transduction. In this study, we report that BRAG1, a putative guanine nucleotide exchange factor for the Arf family of GTP-binding proteins, is a major component of the PSD. BRAG1 was identified in a 190 kDa band in the PSD fraction with the use of mass spectrometry coupled to searching of a protein sequence database. BRAG1 expression is abundant in the adult rat forebrain, and it is strongly enriched in the PSD fraction compared to forebrain homogenate and synaptosomes. Immunocytochemical localization of BRAG1 in dissociated hippocampal neurons shows that it forms discrete clusters that colocalize with the postsynaptic marker PSD-95 at sites along dendrites. BRAG1 contains a Sec7 domain, a domain that catalyzes exchange of GDP for GTP on the Arf family of small GTP-binding proteins. In their GTP-bound active state, Arfs regulate trafficking of vesicles and cytoskeletal structure. We demonstrate that the Sec7 domain of BRAG1 promotes binding of GTP to Arf in vitro. These data suggest that BRAG1 may modulate the functions of Arfs at synaptic sites.
authors.affiliation: Department of Physiology and Neurobiology, University of Connecticut, 75 North Eagleville Road, U-3156, Storrs, CT 06269, USA.
authors.forename: Jessica A
authors.initials: JA
authors.lastname: Murphy
authors.forename: Ole N
authors.initials: ON
authors.lastname: Jensen
authors.forename: Randall S
authors.initials: RS
authors.lastname: Walikonis
mesh_terms: D020823:ADP-Ribosylation Factor 1 / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western / Q000379:methods; D002478:Cells, Cultured; D004347:Drug Interactions; D004622:Embryo, Mammalian; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000493:pharmacokinetics; D006624:Hippocampus / Q000166:cytology; D007150:Immunohistochemistry / Q000379:methods; D008970:Molecular Weight; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D016548:Prosencephalon / Q000166:cytology; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D020539:Sequence Analysis, Protein; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods; D013347:Subcellular Fractions / Q000378:metabolism; D013460:Sulfur Isotopes / Q000493:pharmacokinetics; D013569:Synapses / Q000145:classification / Q000378:metabolism*; D013997:Time Factors
chemical_list: D020662:Guanine Nucleotide Exchange Factors; C516347:Iqsec2 protein, rat; D009419:Nerve Tissue Proteins; C066755:Sec7 guanine nucleotide exchange factors; D013460:Sulfur Isotopes; C033652:postsynaptic density proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D020823:ADP-Ribosylation Factor 1