Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
Mol Biol Cell. 2020 Sep 1;31(19):2139-2155. doi: 10.1091/mbc.E20-03-0168. Epub 2020 Jul 16.
The mechanisms employed in the retention of Golgi resident membrane proteins are diverse and include features such as the composition and length of the protein's transmembrane domain and motifs that mediate direct or indirect associations with COPI-coatomer. However, in sum the current compendium of mechanisms cannot account for the localization of all Golgi membrane proteins, and this is particularly the case for proteins such as the glycosyltransferases. Here we describe a novel mechanism that mediates the steady-state retention of a subset of glycosyltransferases in the Golgi of budding yeast cells. This mechanism is mediated by a deubiquitinase complex composed of Bre5p and Ubp3p. We show that in the absence of this deubiquitinase certain glycosyltransferases are mislocalized to the vacuole, where they are degraded. We also show that Bre5p/Ubp3p clients bind to COPI-coatomer via a series of positively charged amino acids in their cytoplasmically exposed N-termini. Furthermore, we identify two proteins (Ktr3p and Mnn4p) that show a requirement for both Bre5p/Ubp3p as well as the COPI-coatomer-affiliated sorting receptor Vps74p. We also establish that some proteins show a nutrient-dependent role for Vps74p in their Golgi retention. This study expands the repertoire of mechanisms mediating the retention of Golgi membrane proteins.
用于保留驻留在内质网中的膜蛋白的机制多种多样，包括蛋白质跨膜域的组成和长度以及介导与 COPI-衣被小体直接或间接关联的基序等特征。然而，总的来说，当前的机制综述不能解释所有驻留在内质网中的膜蛋白的定位，对于糖基转移酶等蛋白尤其如此。在这里，我们描述了一种介导一部分糖基转移酶在出芽酵母细胞中的内质网中稳定保留的新机制。该机制由 Bre5p 和 Ubp3p 组成的去泛素化酶复合物介导。我们表明，在缺乏这种去泛素化酶的情况下，某些糖基转移酶会错误定位到液泡中，在那里它们被降解。我们还表明，Bre5p/Ubp3p 的靶蛋白通过其细胞质暴露的 N 末端中的一系列正电荷氨基酸与 COPI-衣被小体结合。此外，我们鉴定了两种蛋白质（Ktr3p 和 Mnn4p），它们既需要 Bre5p/Ubp3p，也需要与 COPI-衣被小体相关的分选受体 Vps74p。我们还确定了一些蛋白在它们的 Golgi 保留中显示出对 Vps74p 的营养依赖性作用。这项研究扩展了介导驻留在内质网中的膜蛋白保留的机制谱。
