Retrograde transport of the mannosyltransferase Och1p to the early Golgi requires a component of the COG transport complex
Retrograde transport of the mannosyltransferase Och1p to the early Golgi requires a component of the COG transport complex
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DOI：
10.1074/jbc.m405500200
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发表时间：
2004-09-17
影响因子：
4.8
通讯作者：
Nothwehr, SF
中科院分区：
文献类型：
--
作者：
Bruinsma, P;Spelbrink, RG;Nothwehr, SF
酵母COG复合物被认为在早期高尔基体区室中作为一种囊泡系留复合物发挥作用，但其作用尚未完全了解。COG复合物突变体表现出高尔基体特异性糖基化显著减少以及其他缺陷。在此我们表明，携带COG3温度敏感等位基因cog3 - 202的菌株明显表现出糖基化缺陷，同时呈现出近乎正常的分泌动力学。两种高尔基体甘露糖基转移酶，Och1p和Mnn1p，在cog3 - 202细胞中定位错误。在cog3 - 202细胞中，Och1 - HA存在于比野生型细胞密度更低的膜中。在sed5（ts）和sft1（ts）菌株中，Och1p迅速积累在囊泡样结构中，这与Och1p通过含有Sed5p/Sft1p的SNARE复合物在逆行囊泡上被送回顺式高尔基体相一致。与cog3 - 202细胞相反，sed5ts细胞中含有Och1p的膜比野生型更致密。这些结果共同表明，Och1p不会在cog3 - 202突变体的逆行囊泡中积累，并且与COG复合物在将Och1p分选到逆行囊泡中所起的作用相符。在野生型细胞中，先前已表明Och1p在顺式高尔基体与至少远至晚期高尔基体之间循环。我们发现Och1p在其正常行程中不通过内体循环，这表明Och1p仅参与高尔基体内部循环。然而，Och1p确实使用一种高尔基体后途径进行降解，因为一部分Och1p在液泡中被降解。最令人惊讶的是，Och1p可以使用羧肽酶Y或AP - 3途径到达液泡进行降解。
The yeast COG complex has been proposed to function as a vesicle-tethering complex on an early Golgi compartment, but its role is not fully understood. COG complex mutants exhibit a dramatic reduction in Golgi-specific glycosylation and other defects. Here we show that a strain carrying a COG3 temperature-sensitive allele, cog3-202, clearly exhibited the glycosylation defect while exhibiting nearly normal secretion kinetics. Two Golgi mannosyltransferases, Och1p and Mnn1p, were mislocalized in cog3-202 cells. In cog3-202 cells Och1-HA was found in lighter density membranes than in wild type cells. In sed5(ts) and sft1(ts) strains, Och1p rapidly accumulated in vesicle-like structures consistent with the delivery of Och1p back to the cis-Golgi on retrograde vesicles via a Sed5p/Sft1p-containing SNARE complex. In contrast to cog3-202 cells, the membranes in sed5ts cells that contained Och1p were denser than in wild type. Together these results indicate that Och1p does not accumulate in retrograde vesicles in the cog3-202 mutant and are consistent with the COG complex playing a role in sorting of Och1p into retrograde vesicles. In wild type cells Och1p has been shown previously to cycle between the cis-Golgi and minimally as far as the late Golgi. We find that Och1p does not cycle via endosomes during its normal itinerary suggesting that Och1p engages in intra-Golgi cycling only. However, Och1p does use a post-Golgi pathway for degradation because a portion of Och1p was degraded in the vacuole. Most surprisingly, Och1p can use either the carboxypeptidase Y or AP-3 pathways to reach the vacuole for degradation.