Biochemistry Section, Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany.
Center of Cellular Nanoanalytics Osnabrück (CellNanOs), University of Osnabrück, 49076 Osnabrück, Germany.
Mol Biol Cell. 2018 Nov 1;29(22):2709-2719. doi: 10.1091/mbc.E18-06-0339. Epub 2018 Sep 6.
Endosomes serve as a central sorting station of lipids and proteins that arrive via vesicular carrier from the plasma membrane and the Golgi complex. At the endosome, retromer complexes sort selected receptors and membrane proteins into tubules or vesicles that bud off the endosome. The mature endosome finally fuses with the lysosome. Retromer complexes consist of a cargo selection complex (CSC) and a membrane remodeling part (sorting nexin [SNX]-Bin/amphiphysin/Rvs [BAR], or Snx3 in yeast) and different assemblies of retromer mediate recycling of different cargoes. Due to this complexity, the exact order of events that results in carrier formation is not yet understood. Here, we reconstituted this process on giant unilamellar vesicles together with purified retromer complexes from yeast and selected cargoes. Our data reveal that the membrane remodeling activity of both Snx3 and the SNX-BAR complex is strongly reduced at low concentrations, which can be reactivated by CSC. At even lower concentrations, these complexes still associate with membranes, but only remodel membranes in the presence of their specific cargoes. Our data thus favor a simple model, where cargo functions as a specific trigger of retromer-mediated sorting on endosomes.
内体充当脂质和蛋白质的中央分拣站，这些脂质和蛋白质通过来自质膜和高尔基体复合物的囊泡载体到达。在内体中，逆行转运复合体将选定的受体和膜蛋白分拣到小管或小泡中，这些小管或小泡从小泡中脱离。成熟的内体最终与溶酶体融合。逆行转运复合体由货物选择复合体（CSC）和膜重塑部分（分选连接蛋白[SNX]-Bin/衔接蛋白/Rvs[BAR]，或酵母中的 Snx3）组成，不同的逆行转运复合体组装介导不同货物的循环。由于这种复杂性，导致载体形成的确切顺序尚不清楚。在这里，我们与来自酵母的纯化逆行转运复合体一起，在巨大的单层囊泡上重新构建了这个过程，并选择了货物。我们的数据表明，Snx3 和 SNX-BAR 复合物的膜重塑活性在低浓度下大大降低，CSC 可以使其重新激活。在更低的浓度下，这些复合物仍然与膜结合，但只有在其特定货物存在的情况下才能重塑膜。因此，我们的数据支持一个简单的模型，即货物作为内体中逆行转运介导分拣的特定触发物。
