Xia Yitian, Shang Yuan, Zhang Rongguang, Zhu Jinwei
National Center for Protein Science Shanghai, State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, University of Chinese Academy of Sciences, 333 Haike Road, Shanghai 201203, China.
Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
Biochem J. 2017 Aug 10;474(16):2817-2828. doi: 10.1042/BCJ20170356.
The PSD-95 family of membrane-associated guanylate kinases (MAGUKs) are major synaptic scaffold proteins and play crucial roles in the dynamic regulation of dendritic remodelling, which is understood to be the foundation of synaptogenesis and synaptic plasticity. The guanylate kinase (GK) domain of MAGUK family proteins functions as a phosphor-peptide binding module. However, the GK domain of PSD-95 has been found to directly bind to a peptide sequence within the C-terminal region of neuronal-specific microtubule-associated protein 1A (MAP1A), although the detailed molecular mechanism governing this phosphorylation-independent interaction at the atomic level is missing. In the present study, we determine the crystal structure of PSD-95 GK in complex with the MAP1A peptide at 2.6-Å resolution. The complex structure reveals that, unlike a linear and elongated conformation in the phosphor-peptide/GK complexes, the MAP1A peptide adopts a unique conformation with a stretch of hydrophobic residues far from each other in the primary sequence clustering and interacting with the 'hydrophobic site' of PSD-95 GK and a highly conserved aspartic acid of MAP1A (D2117) mimicking the phosphor-serine/threonine in binding to the 'phosphor-site' of PSD-95 GK. We demonstrate that the MAP1A peptide may undergo a conformational transition upon binding to PSD-95 GK. Further structural comparison of known DLG GK-mediated complexes reveals the target recognition specificity and versatility of DLG GKs.
膜相关鸟苷酸激酶（MAGUKs）家族的突触后密度蛋白95（PSD-95）是主要的突触支架蛋白，在树突重塑的动态调节中起关键作用，而树突重塑被认为是突触发生和突触可塑性的基础。MAGUK家族蛋白的鸟苷酸激酶（GK）结构域作为磷酸肽结合模块发挥作用。然而，尽管在原子水平上控制这种非磷酸化依赖性相互作用的详细分子机制尚不清楚，但已发现PSD-95的GK结构域可直接与神经元特异性微管相关蛋白1A（MAP1A）C端区域内的一个肽序列结合。在本研究中，我们以2.6埃的分辨率确定了与MAP1A肽形成复合物的PSD-95 GK的晶体结构。复合物结构显示，与磷酸肽/GK复合物中的线性和伸长构象不同，MAP1A肽采用独特的构象，其一级序列中一段彼此远离的疏水残基聚集并与PSD-95 GK的“疏水位点”相互作用，并且MAP1A的一个高度保守的天冬氨酸（D2117）在结合PSD-95 GK的“磷酸位点”时模拟磷酸化的丝氨酸/苏氨酸。我们证明，MAP1A肽在与PSD-95 GK结合时可能会发生构象转变。已知的盘状大疱性表皮松解症（DLG）GK介导的复合物的进一步结构比较揭示了DLG GKs的靶标识别特异性和通用性。
