Fu Jie, deSouza Sunita, Ziff Edward B
Howard Hughes Medical Institute, Department of Biochemistry, New York University School of Medicine, New York, New York 10016, USA.
J Neurosci. 2003 Aug 20;23(20):7592-601. doi: 10.1523/JNEUROSCI.23-20-07592.2003.
AMPA receptor-binding protein (ABP) is a multi-postsynaptic density-95/discs large/zona occludens (PDZ) protein that binds to the glutamate receptor 2/3 (GluR2/3) subunits of the AMPA receptor and is implicated in receptor membrane anchorage. A palmitoylated form of ABP localizes to spine heads, whereas a nonpalmitoylated form is found in intracellular clusters. Here, we investigate intracellular cluster formation by ABP and the ability of ABP to associate with GluR2 while in these clusters. We show that ABP interacts with intracellular membranes via the ABP linker I (LI)-set II (SII) subdomain, a region consisting of ABP linker 1 and PDZ4, -5, and -6. This suggests that cluster formation results from LI-SII ABP association with the membrane of a vesicular structure. We present evidence that ABP can self-associate at intracellular membrane surfaces via interactions involving SII. ABP in such membrane clusters can bind and retain GluR2 that has trafficked endocytotically from the plasma membrane. Phosphorylation of GluR2 at serine 880, proximal to the ABP binding site, has been implicated by others in the release of ABP from GluR2 and the mobilization of AMPA receptors for trafficking. We show that binding of GluR2 to ABP blocks phosphorylation of serine 880. This suggests that ABP can stabilize its own association with GluR2. We discuss a model in which ABP can form a protein scaffold at a vesicular membrane that is capable of binding GluR2, leading to formation of an intracellular AMPA receptor pool. Receptors in such a pool may contribute to receptor endocytotic and exocytotic trafficking and recycling.
AMPA受体结合蛋白（ABP）是一种多突触后致密物95/大圆盘蛋白/紧密连接蛋白（PDZ），它与AMPA受体的谷氨酸受体2/3（GluR2/3）亚基结合，并参与受体的膜锚定。ABP的一种棕榈酰化形式定位于棘突头部，而未棕榈酰化的形式则存在于细胞内聚集体中。在这里，我们研究了ABP形成细胞内聚集体的过程以及ABP在这些聚集体中与GluR2结合的能力。我们发现ABP通过ABP连接子I（LI）-集合II（SII）亚结构域与细胞内膜相互作用，该区域由ABP连接子1以及PDZ4、-5和-6组成。这表明聚集体的形成是由于LI-SII ABP与囊泡结构的膜相互作用所致。我们提供的证据表明，ABP可以通过涉及SII的相互作用在细胞内膜表面进行自我结合。这种膜聚集体中的ABP可以结合并保留从质膜内吞运输过来的GluR2。其他人认为，在ABP结合位点附近的丝氨酸880处GluR2的磷酸化与ABP从GluR2上的释放以及AMPA受体运输的动员有关。我们发现GluR2与ABP的结合会阻断丝氨酸880的磷酸化。这表明ABP可以稳定其自身与GluR2的结合。我们讨论了一个模型，其中ABP可以在囊泡膜上形成一个能够结合GluR2的蛋白质支架，从而导致细胞内AMPA受体池的形成。这样一个池中 的受体可能有助于受体的内吞和外排运输以及再循环。
