Curriculum in Genetics and Molecular Biology and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599.
Integrative Program in Biological and Genome Sciences, Department of Biology and Department of Genetics, University of North Carolina, Chapel Hill, NC 27599.
Mol Biol Cell. 2018 Jan 15;29(2):96-110. doi: 10.1091/mbc.E17-11-0627. Epub 2017 Nov 22.
Spinal muscular atrophy (SMA) is caused by homozygous mutations in human Expression of a duplicate gene () primarily results in skipping of exon 7 and production of an unstable protein isoform, SMNΔ7. Although exon skipping is the principal contributor to SMA severity, mechanisms governing stability of survival motor neuron (SMN) isoforms are poorly understood. We used a model system and label-free proteomics to identify the SCF ubiquitin E3 ligase complex as a novel SMN binding partner. SCF interacts with a phosphor degron embedded within the human and fruitfly SMN YG-box oligomerization domains. Substitution of a conserved serine (S270A) interferes with SCF binding and stabilizes SMNΔ7. SMA-causing missense mutations that block multimerization of full-length SMN are also stabilized in the degron mutant background. Overexpression of SMNΔ7, but not wild-type (WT) SMNΔ7, provides a protective effect in SMA model mice and human motor neuron cell culture systems. Our findings support a model wherein the degron is exposed when SMN is monomeric and sequestered when SMN forms higher-order multimers.
脊髓性肌萎缩症（SMA）是由人类中的纯合突变引起的。表达重复基因的主要结果是外显子 7 的跳跃和不稳定的蛋白质异构体 SMNΔ7 的产生。虽然外显子跳跃是 SMA 严重程度的主要原因，但控制运动神经元存活（SMN）异构体稳定性的机制还知之甚少。我们使用无标记蛋白质组学的模型系统来鉴定 SCF 泛素 E3 连接酶复合物作为一种新型的 SMN 结合伴侣。SCF 与人类和果蝇 SMN YG 盒寡聚化结构域内嵌入的磷降解结构域相互作用。保守丝氨酸（S270A）的取代会干扰 SCF 的结合并稳定 SMNΔ7。阻止全长 SMN 多聚化的 SMA 致病错义突变在降解结构域突变体背景下也被稳定下来。SMNΔ7 的过表达，而不是野生型（WT）SMNΔ7，在 SMA 模型小鼠和人类运动神经元细胞培养系统中提供了保护作用。我们的发现支持这样一种模型，即当 SMN 是单体时降解结构域暴露，而当 SMN 形成更高阶的多聚体时降解结构域被隔离。
