Ubiquitin-dependent sorting in endosomes and the TGN

项目总结和摘要 绝大多数生物功能都使用膜包埋蛋白。控制质量和 这些膜蛋白的数量对于这些过程的正常工作至关重要， 破坏错误折叠的蛋白质或去除不再需要的膜蛋白质， 人类疾病。一个用于确定哪些蛋白质经历降解的中心机制是附着 ubiquitin对他们来说泛素是一种小蛋白，在整个细胞界中非常保守。 真核生物当泛素与膜蛋白发生化学连接时，它会导致该蛋白被 被能识别泛素的细胞机制降解。泛素也可以与另一个 泛素，形成聚泛素链。不同的多聚泛素链是通过改变一个泛素 是相互连接的，不同的泛素链被不同的降解机器使用。一个机器 将膜蛋白分类到溶酶体内部，首先将它们分类到腔内小泡中， 在多泡内体/体（MVB）内积累。MVB分选主要使用泛素链， 通过泛素的赖氨酸-63连接，泛素与许多内体蛋白结合， 泛素化的膜蛋白进入腔内小泡。这些腔内囊泡可以是 被递送到内部溶酶体并被降解，或者它们可以作为细胞外分泌， 囊泡/外泌体，其携带并递送内容物至其他细胞以引发一系列生物学效应。 关于蛋白质是如何被分类到内体腔内的， 囊泡以及它们如何被分选为溶酶体与被分选为外泌体的区别。目标1 我将通过研究两种同源分选蛋白的分子机制来解决这些问题。 用于将蛋白质差异分选到管腔内囊泡中，这些囊泡进入溶酶体或成为外泌体。 其他的问题仍然存在，是否泛素连接到膜蛋白的反式， 高尔基体网络，内体和细胞表面，通过它们在细胞内的初始合成， 内质网（所谓的“后ER”蛋白）专门通过MVB途径将它们作为它们的 退化模式。我们发现，ER后蛋白修饰不同类型的多聚泛素链， 使其沿着另一条途径降解。Aim 2将研究这一途径的分子特征， 评估这一途径如何有助于控制膜蛋白的质量和数量。

PROJECT SUMMARY and ABSTRACT The vast majority of biological functions use membrane-embedded proteins. Controlling the quality and quantity of these membrane proteins is critical for these processes to work normally, and defects in the ability to destroy misfolded proteins or getting rid of membrane proteins that are no longer needed cause a plethora of human diseases. A central mechanism used to specify which proteins undergo degradation is attaching ubiquitin to them. Ubiquitin is a small protein that is extremely well-conserved across the entire kingdom of eukaryotic organisms. When ubiquitin is chemically linked to a membrane protein, it causes that protein to be degradaded by cellular machinery that can recognize ubiquitin. Ubiquitin can also be linked to another ubiquitin, forming polyubiquitin chains. Different polyubiquitin chains are made by changing how one ubiquitin is linked to another, and different ubiquitin chains are used by different degradation machines. One machine sorts membrane proteins to the interior of lysosomes by first sorting them into intralumenal vesicles that accumulate within multivesicular endosomes/bodies (MVB). MVB sorting primarily uses ubiquitin chains that are linked via lysine-63 of ubiquitin, which binds to a number of endosomal proteins that cluster and sort ubiquitinated membrane proteins into intralumenal vesicles. These intralumenal vesicles can either be delivered to the interior Lysosomes and be degraded, or they can be secreted as extracellular vesicles/exosomes, that carry and delivery contents to other cells to elicit a range biological effects. Many critical questions remain outstanding about how proteins are sorted into endosomal intralumenal vesicles and what differentiates how they are sorted to Lysosomes versus being sorted into exosomes. Aim1 will address these questions by examining the molecular mechanisms that two homologous sorting proteins use to differentially sort proteins into intralumenal vesicles that go to Lysosomes or become exosomes. Additional questions remain about whether ubiquitin attachment to membrane proteins in the trans- Golgi Network, Endosomes, and cell surface that have made it through their initial synthesis in the endoplasmic reticulum (so-called ‘post-ER’ proteins) exclusively sends them through the MVB pathway as their mode of degradation. We found that post-ER proteins modified with a different type of polyubiquitin chain are sent along a different pathway for degradation. Aim2 will study the molecular features of this pathway and assess how this pathway may contribute to controlling the quality and quantity of membrane proteins.