Lunapark Is a Component of a Ubiquitin Ligase Complex Localized to the Endoplasmic Reticulum Three-way Junctions*
Lunapark Is a Component of a Ubiquitin Ligase Complex Localized to the Endoplasmic Reticulum Three-way Junctions*
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DOI：
10.1074/jbc.m116.737783
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发表时间：
2016-07
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影响因子：
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通讯作者：
Yupeng Zhao;Ting Zhang;H. Huo;Y. Ye;Yanfen Liu
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作者：
Yupeng Zhao;Ting Zhang;H. Huo;Y. Ye;Yanfen Liu
内质网 (ER) 网络由通过动态三路连接点连接的片层和小管组成。 Lunapark (Lnp) 通过拮抗小 GTPase Atlastin 定位并稳定 ER 三路连接点，但 Lnp 如何塑造 ER 网络尚不清楚。在这里，我们使用亲和纯化方法和质谱法将 Lnp 鉴定为 ER 蛋白质量控制泛素连接酶 gp78 的相互作用伙伴。因此，从哺乳动物细胞纯化的Lnp在体外具有泛素连接酶活性。有趣的是，生化分析表明，这种活性不仅可以归因于相关的泛素连接酶，还可以归因于 Lnp 本身所具有的内在泛素连接酶活性。该活性包含在 Lnp N 端 45 个氨基酸中，尽管该片段与任何已知的泛素连接酶基序不具有同源性。尽管 Lnp 与 gp78 相互作用，但它似乎在降解错误折叠的 ER 蛋白方面没有广泛的功能。另一方面，N 端泛素连接酶承载基序是 Lnp 的 ER 三路连接定位所必需的。我们的研究鉴定了一种新型泛素连接酶，并揭示了泛素与内质网形态调节之间的潜在联系。
The endoplasmic reticulum (ER) network comprises sheets and tubules that are connected by dynamic three-way junctions. Lunapark (Lnp) localizes to and stabilizes ER three-way junctions by antagonizing the small GTPase Atlastin, but how Lnp shapes the ER network is unclear. Here, we used an affinity purification approach and mass spectrometry to identify Lnp as an interacting partner of the ER protein quality control ubiquitin ligase gp78. Accordingly, Lnp purified from mammalian cells has a ubiquitin ligase activity in vitro. Intriguingly, biochemical analyses show that this activity can be attributed not only to associated ubiquitin ligase, but also to an intrinsic ubiquitin ligase activity borne by Lnp itself. This activity is contained in the N-terminal 45 amino acids of Lnp although this segment does not share homology to any known ubiquitin ligase motifs. Despite its interaction with gp78, Lnp does not seem to have a broad function in degradation of misfolded ER proteins. On the other hand, the N-terminal ubiquitin ligase-bearing motif is required for the ER three-way junction localization of Lnp. Our study identifies a new type of ubiquitin ligase and reveals a potential link between ubiquitin and ER morphology regulation.