N-Glycosylation at the SynCAM (Synaptic Cell Adhesion Molecule) Immunoglobulin Interface Modulates Synaptic Adhesion
N-Glycosylation at the SynCAM (Synaptic Cell Adhesion Molecule) Immunoglobulin Interface Modulates Synaptic Adhesion
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DOI：
10.1074/jbc.m110.120865
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发表时间：
2010-11-05
影响因子：
4.8
通讯作者：
Biederer, Thomas
中科院分区：
文献类型：
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作者：
Fogel, Adam I.;Li, Yue;Biederer, Thomas
选择黏附分子连接突触前膜和突触后膜，并组织发育中的突触。这些跨突触相互作用的调节是一个重要的神经生物学问题。我们以前已经证明，突触细胞黏附分子(SynCAM)1和2参与同亲和异亲相互作用，桥接突触裂隙，诱导突触前终末。在这里，我们证明了位点特异性的N-糖基化影响粘附性SynCAM相互作用的结构和功能。通过对SynCAM 2的结晶学分析，我们在其IG1结构域的粘附界面对残基ASN(60)上的N-糖链进行了鉴定。对相应的SynCAM 1 IG1结构域的结构模拟表明，其糖基化位点ASN(70)/ASN(104)位于该结构域的结合界面两侧。质谱学和突变研究证实并表征了这三个位点的修饰。这些位点特异的N-聚糖影响SynCAM黏附，但以不同的方式发挥作用。虽然SynCAM 2在ASN(60)处的糖基化减少了粘附性，但SynCAM 1的ASN(70)/ASN(104)处的N-糖链增加了它的相互作用。用唾液酸修饰SynCAM1有助于其结合的糖依赖的加强。在功能上，N-糖基化促进SynCAM1的跨突触相互作用，是突触诱导所必需的。这些结果表明，SynCAM蛋白的N-糖基化对其结合界面有不同的影响，并暗示翻译后修饰是一种调节跨突触黏附的机制。
Select adhesion molecules connect pre- and postsynaptic membranes and organize developing synapses. The regulation of these trans-synaptic interactions is an important neurobiological question. We have previously shown that the synaptic cell adhesion molecules (SynCAMs) 1 and 2 engage in homo- and heterophilic interactions and bridge the synaptic cleft to induce presynaptic terminals. Here, we demonstrate that site-specific N-glycosylation impacts the structure and function of adhesive SynCAM interactions. Through crystallographic analysis of SynCAM 2, we identified within the adhesive interface of its Ig1 domain an N-glycan on residue Asn(60). Structural modeling of the corresponding SynCAM 1 Ig1 domain indicates that its glycosylation sites Asn(70)/Asn(104) flank the binding interface of this domain. Mass spectrometric and mutational studies confirm and characterize the modification of these three sites. These site-specific N-glycans affect SynCAM adhesion yet act in a differential manner. Although glycosylation of SynCAM 2 at Asn(60) reduces adhesion, N-glycans at Asn(70)/Asn(104) of SynCAM 1 increase its interactions. The modification of SynCAM 1 with sialic acids contributes to the glycan-dependent strengthening of its binding. Functionally, N-glycosylation promotes the trans-synaptic interactions of SynCAM 1 and is required for synapse induction. These results demonstrate that N-glycosylation of SynCAM proteins differentially affects their binding interface and implicate post-translational modification as a mechanism to regulate trans-synaptic adhesion.