Hussain Suleman, Ringsevjen Håvard, Egbenya Daniel L, Skjervold Torstein L, Davanger Svend
Division of Anatomy, Department of Molecular Medicine, Institute of Basic Medical Science, University of Oslo Oslo, Norway.
Front Mol Neurosci. 2016 Feb 5;9:10. doi: 10.3389/fnmol.2016.00010. eCollection 2016.
Syntaxins are a family of membrane-integrated proteins that are instrumental in exocytosis of vesicles. Syntaxin-1 is an essential component of the presynaptic exocytotic fusion machinery in the brain and interacts with several other proteins. Syntaxin-1 forms a four-helical bundle complex with proteins SNAP-25 and VAMP2 that drives fusion of vesicles with the plasma membrane in the active zone (AZ). Little is known, however, about the ultrastructural localization of syntaxin-1 at the synapse. We have analyzed the intrasynaptic expression of syntaxin-1 in glutamatergic hippocampal synapses in detail by using quantitative postembedding immunogold labeling. Syntaxin-1 was present in highest concentrations at the presynaptic AZ, supporting its role in transmitter release. Presynaptic plasma membrane lateral to the AZ, as well as presynaptic cytoplasmic (PreCy) vesicles were also labeled. However, syntaxin-1 was also significantly expressed in postsynaptic spines, where it was localized at the postsynaptic density (PSD), at postsynaptic lateral membranes and in postsynaptic cytoplasm. Postsynaptically, syntaxin-1 colocalized in the nanometer range with the N-methyl-D-aspartate (NMDA) receptor subunit NR2B, but only weakly with the AMPA receptor subunits GluA2/3. This observation points to the possibility that syntaxin-1 may be involved with NR2B vesicular trafficking from cytoplasmic stores to the postsynaptic plasma membrane, thus facilitating synaptic plasticity. Confocal immunofluorescence double labeling with PSD-95 and ultrastructural fractionation of synaptosomes also confirm localization of syntaxin-1 at the PSD.
syntaxins是一类膜整合蛋白家族，在囊泡的胞吐作用中起重要作用。Syntaxin-1是大脑中突触前胞吐融合机制的重要组成部分，并与其他几种蛋白质相互作用。Syntaxin-1与蛋白质SNAP-25和VAMP2形成四螺旋束复合物，驱动囊泡与活性区（AZ）的质膜融合。然而，关于Syntaxin-1在突触处的超微结构定位知之甚少。我们通过定量包埋后免疫金标记详细分析了谷氨酸能海马突触中Syntaxin-1的突触内表达。Syntaxin-1在突触前AZ处浓度最高，支持其在递质释放中的作用。AZ外侧的突触前质膜以及突触前细胞质（PreCy）囊泡也被标记。然而，Syntaxin-1在突触后棘中也有显著表达，它定位于突触后致密区（PSD）、突触后外侧膜和突触后细胞质中。在突触后，Syntaxin-1在纳米范围内与N-甲基-D-天冬氨酸（NMDA）受体亚基NR2B共定位，但与AMPA受体亚基GluA2/3的共定位较弱。这一观察结果表明，Syntaxin-1可能参与了NR2B从细胞质储存区到突触后质膜的囊泡运输，从而促进突触可塑性。用PSD-95进行共聚焦免疫荧光双标记和突触体的超微结构分级分离也证实了Syntaxin-1在PSD处的定位。
