Feedback inactivation of D-serine synthesis by NMDA receptor-elicited translocation of serine racemase to the membrane
Feedback inactivation of D-serine synthesis by NMDA receptor-elicited translocation of serine racemase to the membrane
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DOI：
10.1073/pnas.0809442106
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发表时间：
2009-05-05
影响因子：
11.1
通讯作者：
Wolosker, Herman
中科院分区：
文献类型：
--
作者：
Balan, Livia;Foltyn, Veronika N.;Wolosker, Herman
d -丝氨酸是n -甲基d -天冬氨酸受体（NMDARs）的生理凝聚剂，在几种NMDARs依赖性事件中起主要作用。在这项研究中，我们研究了丝氨酸消旋酶（SR）调节d -丝氨酸产生的机制。我们现在报道NMDAR激活促进SR向质膜的易位，这大大降低了酶的活性。从大鼠脑中分离的膜结合SR不能通过高洗涤剂和高盐浓度从膜中提取，表明两者之间存在很强的联系。共定位研究表明，大多数膜结合的SR位于质膜和树突上，而在其他类型的膜上观察到的SR较少。NMDAR的激活促进细胞质SR向膜的易位，导致d -丝氨酸合成减少，而这种作用可以通过阻断NMDAR来避免。在原代神经元培养中，SR向膜的转运被棕榈酰化抑制剂阻断，表明膜结合是由SR的脂肪酸酰化介导的。与此一致的是，我们发现SR在用[3H]棕榈酸酯或[3H]辛酸作为前体转染的神经母细胞瘤细胞中被酰化。与经典的s -棕榈酰化半胱氨酸不同，SR的酰化是通过与丝氨酸或苏氨酸残基形成氧酯键而发生的。此外，我们还发现，在无刺激的基础条件下，SR与膜的稳态结合也需要Thr-227的磷酸化。我们提出，由SR转位到膜上引起的d -丝氨酸合成抑制提供了一种故障安全机制，以防止邻近细胞或突触中的NMDAR过度激活。
D-serine is a physiological coagonist of N-methyl D-aspartate receptors (NMDARs) that plays a major role in several NMDAR-dependent events. In this study we investigate mechanisms regulating D-serine production by the enzyme serine racemase (SR). We now report that NMDAR activation promotes translocation of SR to the plasma membrane, which dramatically reduces the enzyme activity. Membrane-bound SR isolated from rat brain is not extracted from the membrane by high detergent and salt concentration, indicating a strong association. Colocalization studies indicate that most membrane-bound SR is located at the plasma membrane and dendrites, with much less SR observed in other types of membrane. NMDAR activation promotes translocation of the cytosolic SR to the membrane, resulting in reduced D-serine synthesis, and this effect is averted by blockade of NMDARs. In primary neuronal cultures, SR translocation to the membrane is blocked by a palmitoylation inhibitor, indicating that membrane binding is mediated by fatty acid acylation of SR. In agreement, we found that SR is acylated in transfected neuroblastoma cells using [3H] palmitate or [3H] octanoic acid as precursors. In contrast to classical S-palmitoylation of cysteines, acylation of SR occurs through the formation of an oxyester bond with serine or threonine residues. In addition, we show that phosphorylation of Thr-227 is also required for steady-state binding of SR to the membrane under basal, nonstimulated condition. We propose that the inhibition of D-serine synthesis caused by translocation of SR to the membrane provides a fail-safe mechanism to prevent NMDAR overactivation in vicinal cells or synapses.