P24蛋白是一个I型膜蛋白家族，通过COPI和COPII包被的小泡在内质网(ER)和高尔基体之间循环。这些蛋白已被提出作为货物受体的功能，但植物中可能的货物的身份仍然难以捉摸。我们先前从p24δ亚家族的δ-1亚类(p24δ3δ4δ5δ6突变体)中获得了一个影响p24基因的拟南芥(Arabiopsis Thaliana)四突变体。该突变体还降低了其他p24家族蛋白的蛋白水平，并被发现对盐胁迫敏感。
本文，我们使用这个突变体来测试p24蛋白可能参与糖基磷脂酰肌醇(GPI)锚定蛋白向质膜的运输。我们发现，在p24-δ-3-δ-4-δ-5-δ-6突变体细胞中，与其他类型的膜附着的质膜蛋白相比，gpi锚定蛋白主要定位于内质网。P24δ-3δ4δ5δ6突变体瞬时表达p24δ-1亚类的单个成员rfp-p24δ5(依赖于p24δ5的卷曲结构域)，可恢复p24δ-1锚定蛋白的质膜定位。
卷曲-卷曲结构域对p24 GPI锚定蛋白阿拉伯半乳糖蛋白4(Arabinogactan Protein 4)的直接相互作用也是重要的。
这些结果表明，拟南芥p24蛋白参与了GPI锚定蛋白的内质网输出和向质膜的运输。
p24 proteins are a family of type-I membrane proteins that cycle between the endoplasmic reticulum (ER) and the Golgi apparatus via Coat Protein I (COPI)- and COPII-coated vesicles. These proteins have been proposed to function as cargo receptors, but the identity of putative cargos in plants is still elusive. We previously generated an Arabidopsis (Arabidopsis thaliana) quadruple loss-of-function mutant affecting p24 genes from the δ-1 subclass of the p24 delta subfamily (p24δ3δ4δ5δ6 mutant). This mutant also had reduced protein levels of other p24 family proteins and was found to be sensitive to salt stress. Here, we used this mutant to test the possible involvement of p24 proteins in the transport to the plasma membrane of glycosylphosphatidylinositol (GPI)-anchored proteins. We found that GPI-anchored proteins mostly localized to the ER in p24δ3δ4δ5δ6 mutant cells, in contrast to plasma membrane proteins with other types of membrane attachment. The plasma membrane localization of GPI-anchored proteins was restored in the p24δ3δ4δ5δ6 mutant upon transient expression of a single member of the p24 δ-1 subclass, RFP-p24δ5, which was dependent on the coiled-coil domain in p24δ5. The coiled-coil domain was also important for a direct interaction between p24δ5 and the GPI-anchored protein arabinogalactan protein4 (AGP4). These results suggest that Arabidopsis p24 proteins are involved in ER export and transport to the plasma membrane of GPI-anchored proteins.
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