Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011, USA.
Mol Plant. 2008 Nov;1(6):961-76. doi: 10.1093/mp/ssn057. Epub 2008 Oct 3.
Sorting nexins are conserved proteins that function in vesicular trafficking and contain a characteristic phox homology (PX) domain. Here, we characterize the ubiquitously expressed Arabidopsis thaliana sorting nexin AtSNX2b. Sub-cellular fractionation studies indicate that AtSNX2b is peripherally associated with membranes. The AtSNX2b PX domain binds to phosphatidylinositol 3-phosphate in vitro and this association is required for the localization of GFP-AtSNX2b to punctate structures in vivo, identified as the trans-Golgi network, prevacuolar compartment and endosomes. Overexpression of GFP-tagged AtSNX2b produces enlarged GFP-labeled compartments that can also be labeled by the endocytic tracer FM4-64. Endocytic trafficking of FM4-64 to the vacuole is arrested in these GFP-AtSNX2b compartments, and similar FM4-64-accumulating compartments are seen upon overexpression of untagged AtSNX2b. This suggests that exit of membrane components from these enlarged or aggregated endosomes is inhibited. Vacuolar proteins containing an N-terminal propeptide, but not those with a C-terminal propeptide, are also present in these enlarged compartments. We hypothesize that AtSNX2b is involved in vesicular trafficking from endosomes to the vacuole.
分选连接蛋白是一类在囊泡运输中起作用的保守蛋白，它们含有一个特征性的 PH 结构域（PX 结构域）。在这里，我们对广泛表达的拟南芥分选连接蛋白 AtSNX2b 进行了研究。亚细胞分级分离研究表明，AtSNX2b 与膜的外周有关。AtSNX2b 的 PX 结构域在体外与磷脂酰肌醇 3-磷酸结合，这种结合对于 GFP-AtSNX2b 在体内定位于点状结构（被鉴定为高尔基网络、前液泡区隔和内体）是必需的。GFP 标记的 AtSNX2b 的过表达会产生放大的 GFP 标记的隔室，这些隔室也可以被内吞标记物 FM4-64 标记。在这些 GFP-AtSNX2b 隔室内，FM4-64 向液泡的内吞运输被阻断，并且在未标记的 AtSNX2b 的过表达中也可以看到类似的 FM4-64 积累隔室。这表明这些扩大或聚集的内体中膜成分的出口被抑制。含有 N 端前肽的液泡蛋白，而不是含有 C 端前肽的液泡蛋白，也存在于这些扩大的隔室内。我们假设 AtSNX2b 参与了从内体到液泡的囊泡运输。
