Wenzel Dirk, Schauermann Gaby, von Lüpke Anke, Hinz Giselbert
Abteilung für Strukturelle Zellphysiologie, Albrecht-von-Haller Institut für Pflanzenwissenschaften, Georg-August Universität Göttingen, Germany.
Traffic. 2005 Jan;6(1):45-55. doi: 10.1111/j.1600-0854.2004.00243.x.
Developing pea seeds contain two functionally distinct vacuoles--lytic vacuoles and protein storage vacuoles (PSV). The Golgi apparatus of these cells has to discriminate between proteins destined for these vacuolar compartments. Whereas it is known that sorting into the lytic vacuole is performed via the conserved clathrin-coated vesicle pathway, sorting of proteins into the protein storage vacuole remains enigmatic. In developing pea cotyledons, the major storage proteins are sorted via 'dense vesicles'. In this report we examined the sorting of a minor protein of the protein storage vacuole, the sucrose-binding-protein homolog (SBP), along the secretory pathway employing immunoelectron microscopy on cryosectioned pea cotyledons. SBP follows the same vesicular route into the PSV as the main storage proteins legumin and vicilin, via the dense-vesicles. Furthermore, legumin and SBP are sorted together into the same dense vesicle population at the stack. Although soluble cargo proteins of the dense vesicles, they show a stratified distribution in the lumen of the dense vesicles. Whereas the legumin label is equally distributed across the lumen, the SBP label is concentrated at the membrane of the vesicle. This observation is discussed with respect to a putative receptor-mediated sorting of the proteins into the dense vesicles.
发育中的豌豆种子含有两种功能不同的液泡——溶酶体液泡和蛋白质储存液泡（PSV）。这些细胞的高尔基体必须区分运往这些液泡区室的蛋白质。虽然已知通过保守的网格蛋白包被囊泡途径将蛋白质分选到溶酶体液泡中，但将蛋白质分选到蛋白质储存液泡中的过程仍然是个谜。在发育中的豌豆子叶中，主要的储存蛋白质通过“致密囊泡”进行分选。在本报告中，我们利用冷冻切片豌豆子叶的免疫电子显微镜技术，研究了蛋白质储存液泡的一种次要蛋白质——蔗糖结合蛋白同源物（SBP）沿着分泌途径的分选过程。SBP与主要储存蛋白质豆球蛋白和豌豆球蛋白一样，通过致密囊泡沿着相同的囊泡途径进入PSV。此外，豆球蛋白和SBP在高尔基体堆叠处被分选到同一群致密囊泡中。尽管它们是致密囊泡的可溶性货物蛋白，但在致密囊泡腔内呈现分层分布。豆球蛋白标记物在整个腔内均匀分布，而SBP标记物则集中在囊泡膜上。针对蛋白质通过假定的受体介导分选进入致密囊泡的过程，对这一观察结果进行了讨论。
