Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
Biochem Biophys Res Commun. 2010 Jul 30;398(3):537-41. doi: 10.1016/j.bbrc.2010.06.114. Epub 2010 Jul 1.
Glutamate receptor delta2 (GluD2) is selectively expressed on the postsynaptic spines at parallel-fiber (PF)-Purkinje neuron (PN) synapses. GluD2 knockout mice show a reduced number of PF-PN synapses, suggesting that GluD2 is involved in synapse formation. Recent studies revealed that GluD2 induces presynaptic differentiation in a manner dependent on its N-terminal domain (NTD) through binding of Cbln1 secreted from cerebellar granule neurons. However, the underlying mechanism of the specific binding of the NTD to Cbln1 remains elusive. Here, we have identified the flap loop (Arg321-Trp339) in the NTD of GluD2 (GluD2-NTD) as a crucial region for the binding to Cbln1 and the induction of presynaptic differentiation. Both induction of presynaptic differentiation and binding of Cbln1 were abolished in the HEK cells expressing not wild-type GluD2 but GluD2 with mutations in the flap loop. Especially, single amino acid substitution of either Arg321 or Trp323 to alanine was sufficient to disable the GluD2 function. Finally, a homology model of GluD2-NTD suggested that the flap loop is located at the distal end, which appears consistent with an interaction with Cbln1 and a presynaptic varicosity.
谷氨酸受体 delta2（GluD2）选择性地表达在平行纤维（PF）-浦肯野神经元（PN）突触的突触后棘上。GluD2 敲除小鼠的 PF-PN 突触数量减少，表明 GluD2 参与了突触形成。最近的研究表明，GluD2 通过结合小脑颗粒神经元分泌的 Cbln1，以依赖其 N 端结构域（NTD）的方式诱导突触前分化。然而，NTD 与 Cbln1 的特异性结合的潜在机制仍不清楚。在这里，我们确定了 GluD2（GluD2-NTD）NTD 中的瓣环（Arg321-Trp339）是与 Cbln1 结合和诱导突触前分化的关键区域。在表达野生型 GluD2 而非突变 GluD2 的 HEK 细胞中，诱导突触前分化和 Cbln1 结合均被消除。特别是 Arg321 或 Trp323 突变为丙氨酸足以使 GluD2 功能丧失。最后，GluD2-NTD 的同源模型表明，瓣环位于远端，这与与 Cbln1 的相互作用和突触前膨体一致。
