Murphy Jessica A, Jensen Ole N, Walikonis Randall S
Department of Physiology and Neurobiology, University of Connecticut, 75 North Eagleville Road, U-3156, Storrs, CT 06269, USA.
Brain Res. 2006 Nov 20;1120(1):35-45. doi: 10.1016/j.brainres.2006.08.096. Epub 2006 Oct 11.
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.
兴奋性突触处的突触后致密区（PSD）是谷氨酸能受体及相关蛋白的动态复合体，它控制突触结构并协调信号转导。在本研究中，我们报告称BRAG1是PSD的主要成分，它是一种假定的GTP结合蛋白Arf家族的鸟嘌呤核苷酸交换因子。利用质谱联用蛋白质序列数据库搜索，在PSD组分的一条190 kDa条带中鉴定出了BRAG1。BRAG1在成年大鼠前脑表达丰富，与前脑匀浆和突触体相比，它在PSD组分中高度富集。BRAG1在解离的海马神经元中的免疫细胞化学定位显示，它形成离散的簇，与树突上的突触后标记物PSD-95共定位。BRAG1含有一个Sec7结构域，该结构域催化小GTP结合蛋白Arf家族上的GDP与GTP交换。处于GTP结合的活性状态时，Arf调节囊泡运输和细胞骨架结构。我们证明BRAG1的Sec7结构域在体外促进GTP与Arf结合。这些数据表明BRAG1可能在突触部位调节Arf的功能。
