Sans N, Petralia R S, Wang Y X, Blahos J, Hell J W, Wenthold R J
Laboratory of Neurochemistry, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland 20892, USA.
J Neurosci. 2000 Feb 1;20(3):1260-71. doi: 10.1523/JNEUROSCI.20-03-01260.2000.
The membrane-associated guanylate kinases [Chapsyn-110/postsynaptic density-93 (PSD-93), synapse-associated protein-90 (SAP-90)/PSD-95, and SAP-102] are believed to cluster and anchor NMDA receptors at the synapse and to play a role in signal transduction. We have investigated the developmental changes in expression of these proteins in rat hippocampus using biochemical analyses and quantitative immunogold electron microscopy. At postnatal day 2 (P2), SAP-102 was highly expressed, whereas PSD-93 and PSD-95 were low. SAP-102 expression increased during the first week, stayed stable through P35, and showed a reduced expression at 6 months. From P2 through 6 months, PSD-93 and PSD-95 increased. For PSD-95, the percent of labeled synapses increased almost threefold with age, whereas the number of gold particles per labeled synapse did not change significantly, suggesting that the increase in PSD-95 is attributable primarily to an increase in the number of synapses containing PSD-95. In contrast, for SAP-102, both percent labeled synapses and the number of gold particles per labeled synapse decreased during this time. From Western blots of hippocampus and immunogold analysis of CA1 synapses, the high expression of NR2B at P2 coincides with the high level of SAP-102 at synapses, whereas the later expression of NR2A coincides with that of PSD-93 and PSD-95. To determine whether the changes in PSD-93/95 and SAP-102 reflect preferred associations with NR2A and NR2B, respectively, we measured co-immunoprecipitation in the adult hippocampus. These studies suggest that there is a preference for complexes of NR2A/PSD-93/95 and NR2B/SAP-102. These results indicate that individual receptor-associated proteins may have specific functions that are critical to synapse development.
膜相关鸟苷酸激酶（Chapsyn-110/突触后致密蛋白-93（PSD-93）、突触相关蛋白-90（SAP-90）/PSD-95和SAP-102）被认为在突触处聚集并锚定N-甲基-D-天冬氨酸（NMDA）受体，并在信号转导中发挥作用。我们使用生化分析和定量免疫金电子显微镜研究了大鼠海马中这些蛋白质表达的发育变化。在出生后第2天（P2），SAP-102高度表达，而PSD-93和PSD-95表达较低。SAP-102的表达在第一周增加，在P35之前保持稳定，并在6个月时表达降低。从P2到6个月，PSD-93和PSD-95增加。对于PSD-95，标记突触的百分比随年龄增长几乎增加了三倍，而每个标记突触的金颗粒数量没有显著变化，这表明PSD-95的增加主要归因于含有PSD-95的突触数量的增加。相比之下，对于SAP-102，在此期间标记突触的百分比和每个标记突触的金颗粒数量均下降。从海马的蛋白质印迹和CA1突触的免疫金分析来看，P2时NR2B的高表达与突触处SAP-102的高水平一致，而NR2A的后期表达与PSD-93和PSD-95的表达一致。为了确定PSD-93/95和SAP-102的变化是否分别反映了与NR2A和NR2B的优先结合，我们在成年海马中测量了共免疫沉淀。这些研究表明，存在NR2A/PSD-93/95和NR2B/SAP-102复合物的偏好。这些结果表明，单个受体相关蛋白可能具有对突触发育至关重要的特定功能。
