神經細胞間產生聯結的區域叫作突觸(synapses)，突觸的構造包括軸突(axons)末端特化形成的前突觸(pre-synaptic terminal)、樹突(dendrites)前端特化形成的後突觸(post-synaptic terminal)以及兩者之間的連結synaptic cleft所組成。後突觸質密區(post-synaptic density, 簡稱PSD)就位於後突觸膜下方，一般認為它在突觸的結構和功能上扮演重要的角色。
本研究中，我們分別從豬腦中的大腦皮質和小腦二區域分離出PSD，SDS-PAGE和Western blotting分析指出大腦和小腦的PSD有類似的構造，但個別組成蛋白的多寡卻存在明顯的差異。接著，我們用奈米深度標定的方法(Nano-Depth-Tagging, NDT)分析不同蛋白質在PSD內部的深度位置。這個方法主要有三個組成，agarose beads、化學聯接劑和不同長度的胜肰鏈。經由已知的四層蛋白質複合物(Four proteins complex, FPC)驗證後，此方法可提供不同蛋白質在PSD內部的深度分佈情形。實驗結果指出，在大腦皮質和小腦的PSD中, glutamate receptors, actin和actin binding proteins位於距表面深度10 nm以內的周圍區域，而一些結構性蛋白，tubulin和microtubule-binding proteins，以及與細胞膜結構有關的蛋白均發現位於距表面深度大於10 nm的內部區域。最後，利用免疫吸附的方法，PSD-95、α-tubulin、elongation factor-1α和calcium, calmodulin-dependent protein kinase II α subunit這四種蛋白質的binding partner proteins均可被鑑別出來。總言之，經由實驗分析，我們提出一個PSD分子結構模型，此外，本研究亦指出大腦和小腦的PSD在蛋白質組成上存在著明顯的相似度。

Postsynaptic density (PSD) is a protein supramolecule lying underneath the postsynaptic membrane of excitatory synapses and has been implicated to play important roles in synaptic structure and function in mammalian central nervous system. Here, PSDs were isolated from two distinct regions of porcine brain, cerebral cortex and cerebellum. SDS-PAGE and Western blotting analyses indicated that cerebral and cerebellar PSDs consisted of a similar set of proteins with noticeable differences in the abundance of various proteins between these samples. Subsequently, protein localization in these PSDs was analyzed by using the Nano-Depth-Tagging (NDT) method. This method involved the use of three synthetic reagents, as agarose beads whose surface was covalently linked with a fluorescent, photoactivable and cleavable chemical crosslinker by spacers of varied lengths. After its application was verified by using a synthetic complex consisting of four layers of different proteins, the NDT method was used here to yield information concerning the depth distribution of various proteins in the PSD. The results indicated that in both cerebral and cerebellar PSDs, glutamate receptors, actin and actin binding proteins resided in the peripheral regions within ~10 nm deep from the surface and that scaffold proteins, tubulin subunits, microtubule-binding proteins, membrane cytoskeleton proteins found in mammalian erythrocytes resided in the interiors deeper than 10 nm from the surface in the PSD. Finally, by using immunoabsorption method, binding partner proteins of two proteins residing in the interiors, PSD-95 and α-tubulin, and those of two proteins residing in the peripheral regions, elongation factor-1α and calcium, calmodulin-dependent protein kinase II α subunit, of cerebral and cerebellar PSDs were identified. Overall, the results indicate a striking similarity in protein organization between the PSDs isolated from porcine cerebral cortex and cerebellum. A model of the molecular structure of the PSD has also been proposed here.

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