Hinz Giselbert, Colanesi Sarah, Hillmer Stefan, Rogers John C, Robinson David G
Department of Cell Biology, Heidelberg Institute for Plant Sciences, University of Heidelberg, 69120 Heidelberg, Germany.
Traffic. 2007 Oct;8(10):1452-64. doi: 10.1111/j.1600-0854.2007.00625.x. Epub 2007 Aug 13.
Using immunogold electron microscopy, we have investigated the relative distribution of two types of vacuolar sorting receptors (VSR) and two different types of lumenal cargo proteins, which are potential ligands for these receptors in the secretory pathway of developing Arabidopsis embryos. Interestingly, both cargo proteins are deposited in the protein storage vacuole, which is the only vacuole present during the bent-cotyledon stage of embryo development. Cruciferin and aleurain do not share the same pattern of distribution in the Golgi apparatus. Cruciferin is mainly detected in the cis and medial cisternae, especially at the rims where storage proteins aggregate into dense vesicles (DVs). Aleurain is found throughout the Golgi stack, particularly in the trans cisternae and trans Golgi network where clathrin-coated vesicles (CCVs) are formed. Nevertheless, aleurain was detected in both DV and CCV. VSR-At1, a VSR that recognizes N-terminal vacuolar sorting determinants (VSDs) of the NPIR type, localizes mainly to the trans Golgi and is hardly detectable in DV. Receptor homology-transmembrane-RING H2 domain (RMR), a VSR that recognizes C-terminal VSDs, has a distribution that is very similar to that of cruciferin and is found in DV. Our results do not support a role for VSR-At1 in storage protein sorting, instead RMR proteins because of their distribution similar to that of cruciferin in the Golgi apparatus and their presence in DV are more likely candidates. Aleurain, which has an NPIR motif and seems to be primarily sorted via VSR-At1 into CCV, also possesses putative hydrophobic sorting determinants at its C-terminus that could allow the additional incorporation of this protein into DV.
利用免疫金电子显微镜技术，我们研究了两种液泡分选受体（VSR）和两种不同类型的腔内货物蛋白的相对分布情况，这些蛋白是拟南芥发育胚胎分泌途径中这些受体的潜在配体。有趣的是，这两种货物蛋白都沉积在蛋白储存液泡中，蛋白储存液泡是胚胎发育弯子叶阶段唯一存在的液泡。十字花科贮藏蛋白和 aleurain 在高尔基体中的分布模式不同。十字花科贮藏蛋白主要在顺面和中间潴泡中检测到，尤其是在储存蛋白聚集形成致密小泡（DV）的边缘。Aleurain 在整个高尔基体堆栈中都有发现，特别是在形成网格蛋白包被小泡（CCV）的反面潴泡和反式高尔基体网络中。然而，在 DV 和 CCV 中都检测到了 aleurain。VSR-At1 是一种识别 NPIR 型 N 端液泡分选决定簇（VSD）的 VSR，主要定位于反式高尔基体，在 DV 中几乎检测不到。受体同源-跨膜-RING H2 结构域（RMR）是一种识别 C 端 VSD 的 VSR，其分布与十字花科贮藏蛋白非常相似，且存在于 DV 中。我们的结果不支持 VSR-At1 在储存蛋白分选中发挥作用，相反，由于 RMR 蛋白在高尔基体中的分布与十字花科贮藏蛋白相似且存在于 DV 中，它们更有可能是候选者。Aleurain 具有 NPIR 基序，似乎主要通过 VSR-At1 分选到 CCV 中，其 C 端也具有推定的疏水性分选决定簇，这可能允许该蛋白额外掺入 DV 中。
