ER network formation and membrane fusion by atlastin1/SPG3A disease variants.
ER network formation and membrane fusion by atlastin1/SPG3A disease variants.
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DOI：
10.1091/mbc.e14-10-1447
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发表时间：
2015-05-01
影响因子：
3.3
通讯作者：
Lee TH
中科院分区：
文献类型：
--
作者：
Ulengin I;Park JJ;Lee TH
阿联蛋白催化gtp依赖的膜融合形成内质网。atlastin1突变可引起遗传性痉挛性截瘫（HSP），提示内质网膜融合缺陷可引起HSP。令人惊讶的是，一些疾病变异在内质网形成和膜融合的检测中是有功能的，这就需要重新思考atlastin1突变导致热休克的原因。至少38种不同的神经元atlastin1/SPG3A GTPase错义突变与常染色体显性遗传性痉挛性截瘫（HSP）有关，HSP是一种运动神经疾病，表现为下肢无力和痉挛以及皮质脊髓运动神经元的长度依赖性轴突病。因为至少在非神经元细胞中，atlasatin GTPase足以催化膜融合并需要形成内质网，因此从逻辑上认为，由于融合活性受损而导致的内质网膜形态发生缺陷是spg3a相关HSP的主要驱动因素。在这里，我们分析了一个已建立的atlastin1/SPG3A疾病变异的子集，使用基于细胞的atlastin1介导的ER网络形成和生化分析atlastin1催化的GTP水解、二聚体形成和膜融合。正如预期的那样，一些变体表现出明显的缺陷。然而，令人惊讶的是，至少有两种疾病变体，其中一种在SPG3A HSP患者中最常见，在所有检测中都显示出野生型的活性水平。相同的变体也能够共同重新分配内质网定位的REEP1，这是最近发现的一种需要其催化活性的atlastins功能。综上所述，这些发现表明，atlastin1的膜融合活性缺陷可能是HSP病因的关键因素，但不是必需的。
Atlastin catalyzes GTP-dependent membrane fusion to form the ER network. Mutations in atlastin1 cause the disease hereditary spastic paraplegia (HSP), implying that defects in ER membrane fusion cause HSP. Surprisingly, several disease variants are functional in assays for ER network formation and membrane fusion, warranting rethinking of HSP causation by atlastin1 mutations. At least 38 distinct missense mutations in the neuronal atlastin1/SPG3A GTPase are implicated in an autosomal dominant form of hereditary spastic paraplegia (HSP), a motor-neurological disorder manifested by lower limb weakness and spasticity and length-dependent axonopathy of corticospinal motor neurons. Because the atlastin GTPase is sufficient to catalyze membrane fusion and required to form the ER network, at least in nonneuronal cells, it is logically assumed that defects in ER membrane morphogenesis due to impaired fusion activity are the primary drivers of SPG3A-associated HSP. Here we analyzed a subset of established atlastin1/SPG3A disease variants using cell-based assays for atlastin-mediated ER network formation and biochemical assays for atlastin-catalyzed GTP hydrolysis, dimer formation, and membrane fusion. As anticipated, some variants exhibited clear deficits. Surprisingly however, at least two disease variants, one of which represents that most frequently identified in SPG3A HSP patients, displayed wild-type levels of activity in all assays. The same variants were also capable of co-redistributing ER-localized REEP1, a recently identified function of atlastins that requires its catalytic activity. Taken together, these findings indicate that a deficit in the membrane fusion activity of atlastin1 may be a key contributor, but is not required, for HSP causation.