Laforin, the dual-phosphatase responsible for Lafora disease, interacts with R5 (PTG), a regulatory subunit of protein phosphatase-1 that enhances glycogen accumulation
Laforin, the dual-phosphatase responsible for Lafora disease, interacts with R5 (PTG), a regulatory subunit of protein phosphatase-1 that enhances glycogen accumulation
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DOI：
10.1093/hmg/ddg340
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发表时间：
2003-12-01
影响因子：
3.5
通讯作者：
de Córdoba, SR
中科院分区：
文献类型：
--
作者：
Fernández-Sánchez, ME;Criado-García, O;de Córdoba, SR
Lafora型进行性肌阵挛癫痫（LD，MIM 254780）是一种致死性常染色体隐性遗传疾病，其特征为存在进行性神经功能恶化、肌阵挛、癫痫和称为Lafora小体的葡聚糖细胞内包涵体。Lafora小体类似于分支减少的糖原，表明糖原代谢发生了改变。连锁分析和纯合性定位定位EPM 2A，LD的主效基因，染色体6 q24。EPM 2A编码331个氨基酸的蛋白质（命名为laforin），其具有两个结构域，双特异性磷酸酶结构域和碳水化合物结合结构域。在这里，我们表明，此外，laforin相互作用与自身和糖原靶向调节亚基R5的蛋白磷酸酶1（PP 1）。R5是鼠糖原靶向蛋白的人同源物，该蛋白也作为分子支架，在细胞内糖原颗粒处组装PP 1及其底物糖原合酶。通过下拉和共定位实验证实了laforin-R5相互作用。相互作用需要全长laforin。然而，R5的最小中心区域（氨基酸116-238），包括糖原和糖原合酶的结合位点，足以与laforin相互作用。点突变的糖原脱氢酶结合位点完全阻断与laforin的相互作用。在LD患者中发现的大多数EPM 2A错义突变导致缺乏磷酸酶活性、缺乏与糖原的结合以及缺乏与R5的相互作用。有趣的是，我们发现LD相关的EPM 2A错义突变G240 S对laforin的磷酸酶或糖原结合活性没有影响，但破坏了与R5的相互作用，表明与R5的结合对laforin功能至关重要。这些结果将laforin置于与细胞内糖原颗粒相关的多蛋白复合物的背景下，加强了laforin参与糖原代谢调节的概念。
Progressive myoclonus epilepsy of Lafora type (LD, MIM 254780) is a fatal autosomal recessive disorder characterized by the presence of progressive neurological deterioration, myoclonus, epilepsy and polyglucosan intracellular inclusion bodies, called Lafora bodies. Lafora bodies resemble glycogen with reduced branching, suggesting an alteration in glycogen metabolism. Linkage analysis and homozygosity mapping localized EPM2A, a major gene for LD, to chromosome 6q24. EPM2A encodes a protein of 331 amino acids (named laforin) with two domains, a dual-specificity phosphatase domain and a carbohydrate binding domain. Here we show that, in addition, laforin interacts with itself and with the glycogen targeting regulatory subunit R5 of protein phosphatase 1 (PP1). R5 is the human homolog of the murine Protein Targeting to Glycogen, a protein that also acts as a molecular scaffold assembling PP1 with its substrate, glycogen synthase, at the intracellular glycogen particles. The laforin-R5 interaction was confirmed by pull-down and co-localization experiments. Full-length laforin is required for the interaction. However, a minimal central region of R5 (amino acids 116-238), including the binding sites for glycogen and for glycogen synthase, is sufficient to interact with laforin. Point-mutagenesis of the glycogen synthase-binding site completely blocked the interaction with laforin. The majority of the EPM2A missense mutations found in LD patients result in lack of phosphatase activity, absence of binding to glycogen and lack of interaction with R5. Interestingly, we have found that the LD-associated EPM2A missense mutation G240S has no effect on the phosphatase or glycogen binding activities of laforin but disrupts the interaction with R5, suggesting that binding to R5 is critical for the laforin function. These results place laforin in the context of a multiprotein complex associated with intracellular glycogen particles, reinforcing the concept that laforin is involved in the regulation of glycogen metabolism.