Multivesicular body sorting: Ubiquitin ligase Rsp5 is required for the modification and sorting of carboxypeptidase S
Multivesicular body sorting: Ubiquitin ligase Rsp5 is required for the modification and sorting of carboxypeptidase S
复制标题
DOI：
10.1091/mbc.e03-07-0473
复制
发表时间：
2004-02-01
影响因子：
3.3
通讯作者：
Emr, SD
中科院分区：
文献类型：
--
作者：
Katzmann, DJ;Sarkar, S;Emr, SD
多泡体（MVB）分选途径提供了将跨膜蛋白递送到溶酶体/液泡腔中的机制。最近的研究表明，泛素修饰作为顺式信号将货物分选到该途径中。在这里，我们提出了遗传选择的结果，旨在确定突变体MVB货物错配。该选择鉴定了泛素连接酶Rsp（Rsp 5 -326）中的点突变。在允许的温度下，该突变体对于泛素依赖性MVB货物前体羧肽酶S（pCPS）的泛素化和分选是特异性缺陷的，但不是配体诱导的Ste 2的泛素化。先前的研究暗示Tul 1是负责pCPS的MVB分选的泛素连接酶。然而，我们没有检测到缺陷的分拣或泛素化的pCPS在tul 1突变体。我们以前已经表明，Fab 1磷脂酰肌醇3-磷酸5-激酶也需要MVB分选pCPS，但不是Ste 2。然而，我们的分析表明，fab 1突变体不表现出缺陷的pCPS的泛素化。因此，Rsp 5和Fab 1在靶向生物合成的MVB货物中发挥独特且重要的作用。然而，尽管Rsp 5似乎是负责货物泛素化，Fab 1的确切作用仍有待阐明。
The multivesicular body (MVB) sorting pathway provides a mechanism for delivering transmembrane proteins into the lumen of the lysosome/vacuole. Recent studies demonstrated that ubiquitin modification acts in cis as a signal for the sorting of cargoes into this pathway. Here, we present results from a genetic selection designed to identify mutants that missort MVB cargoes. This selection identified a point mutation in ubiquitin ligase Rsp (Rsp5-326). At the permissive temperature, this mutant is specifically defective for ubiquitination and sorting of the ubiquitin-dependent MVB cargo precursor carboxypeptidase S (pCPS), but not ligand-induced ubiquitination of Ste2. A previous study implicated Tul1 as the ubiquitin ligase responsible for MVB sorting of pCPS. However, we detected no defect in either the sorting or ubiquitination of pCPS in tul1 mutants. We had previously shown that Fab1 phosphatidylinositol 3-phosphate 5-kinase is also required for MVB sorting of pCPS, but not Ste2. However, our analyses reveal that fab1 mutants do not exhibit a defect in ubiquitination of pCPS. Thus, both Rsp5 and Fab1 play distinct, and essential roles in the targeting of biosynthetic MVB cargoes. However, whereas Rsp5 seems to be responsible for cargo ubiquitination, the precise role for Fab1 remains to be elucidated.