Creative Research Institution, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 001-0021, Japan.
J Neurosci. 2011 Nov 9;31(45):16261-8. doi: 10.1523/JNEUROSCI.0002-11.2011.
Synapses are asymmetric structures that are specialized for neuronal signal transduction. A unique set of proteins is present at the presynaptic active zone, which is a core structure essential for neurotransmitter release. In Caenorhabditis elegans HSN neurons, SYD-2, a Liprin-α family protein, acts together with a GAP protein SYD-1 to promote presynaptic assembly. Previous studies have shown that elevating the activity of syd-2 can bypass the requirement of syd-1. Liprin-α proteins are composed of coiled-coil-rich regions in the N-terminal half, which mediate interactions with adapter proteins at the presynaptic active zone, and three SAM domains in the C terminus, which bind proteins such as LAR receptor tyrosine phosphatase. To address the molecular mechanism by which SYD-2 activity is regulated, we performed structure-function studies. By monitoring the ability of SYD-2 transgenes to rescue syd-2(lf) and to suppress syd-1(lf) phenotypes in HSN neuron synapses, we identified the N-terminal half of SYD-2 as minimally required for rescuing syd-2(lf) phenotypes. A highly conserved short coiled-coil segment named Liprin Homology 1 (LH1) domain is both necessary and sufficient to suppress syd-1(lf) defects. We show that the LH1 domain forms a dimer and promotes further oligomerization and/or complex formation of SYD-2/Liprin-α proteins. The role of the LH1 domain in presynaptic assembly can be partially complemented by artificial dimerization. These findings suggest a model by which the self-assembly of SYD-2/Liprin-α proteins mediated by the coiled-coil LH1 domain is one of the key steps to the accumulation of presynaptic components at nascent synaptic junctions.
突触是专门用于神经元信号转导的不对称结构。一组独特的蛋白质存在于突触前活性区,这是神经递质释放所必需的核心结构。在秀丽隐杆线虫 HSN 神经元中,Liprin-α 家族蛋白 SYD-2 与 GAP 蛋白 SYD-1 一起作用,促进突触前装配。先前的研究表明,提高 syd-2 的活性可以绕过 syd-1 的要求。Liprin-α 蛋白由富含卷曲螺旋的区域组成,位于 N 端的一半,介导与突触前活性区的衔接蛋白相互作用,C 端的三个 SAM 结构域结合蛋白,如 LAR 受体酪氨酸磷酸酶。为了解决 SYD-2 活性调节的分子机制,我们进行了结构功能研究。通过监测 SYD-2 转基因在 HSN 神经元突触中拯救 syd-2(lf)和抑制 syd-1(lf)表型的能力,我们确定 SYD-2 的 N 端一半是拯救 syd-2(lf)表型所必需的最小区域。一个高度保守的短卷曲螺旋段命名为 Liprin Homology 1 (LH1) 结构域,既是必需的,也是充分的,以抑制 syd-1(lf)缺陷。我们表明,LH1 结构域形成二聚体,并促进 SYD-2/Liprin-α 蛋白的进一步寡聚化和/或形成复合物。LH1 结构域在突触前装配中的作用可以部分由人工二聚化来补充。这些发现提出了一个模型,即由卷曲螺旋 LH1 结构域介导的 SYD-2/Liprin-α 蛋白的自组装是突触前成分在新生突触连接处积累的关键步骤之一。