Instituto de Investigación Médica Mercedes y Martín Ferreyra, INIMEC - CONICET, Friuli 2434, Córdoba, Argentina.
Biochem J. 2010 Apr 28;428(1):33-45. doi: 10.1042/BJ20100096.
The parasite Giardia lamblia possesses PVs (peripheral vacuoles) that function as both endosomes and lysosomes and are implicated in the adaptation, differentiation and survival of the parasite in different environments. The mechanisms by which Giardia traffics essential proteins to these organelles and regulates their secretion have important implications in the control of parasite dissemination. In the present study, we describe the participation of the heterotetrameric clathrin-adaptor protein gAP2 (Giardia adaptor protein 2) complex in lysosomal protein trafficking. A specific monoclonal antibody against the medium subunit (gmu2) of gAP2 showed localization of this complex to the PVs, cytoplasm and plasma membrane in the growing trophozoites. gAP2 also co-localized with clathrin in the PVs, suggesting its involvement in endocytosis. Uptake experiments using standard molecules for the study of endocytosis revealed that gAP2 specifically participated in the endocytosis of LDL (low-density lipoprotein). Targeted down-regulation of the gene encoding gmu2 in growing and encysting trophozoites resulted in a large decrease in the amount of cell growth and cyst wall formation, suggesting a distinct mechanism in which gAP2 is directly involved in both endocytosis and vesicular trafficking.
寄生虫蓝氏贾第鞭毛虫拥有作为内体和溶酶体发挥作用的 PVs（外周液泡），并与寄生虫在不同环境中的适应、分化和存活有关。贾第虫将必需蛋白运输到这些细胞器并调节其分泌的机制对寄生虫传播的控制具有重要意义。在本研究中，我们描述了异四聚体网格蛋白衔接蛋白 gAP2（贾第虫衔接蛋白 2）复合物在溶酶体蛋白运输中的参与。针对 gAP2 的中等亚基（gmu2）的特异性单克隆抗体显示该复合物在生长的滋养体中定位于 PVs、细胞质和质膜。gAP2 也与 PVs 中的网格蛋白共定位，表明其参与了内吞作用。使用内吞作用研究的标准分子进行的摄取实验表明，gAP2 特异性参与了 LDL（低密度脂蛋白）的内吞作用。在生长和囊形成的滋养体中靶向下调编码 gmu2 的基因导致细胞生长和囊壁形成的大量减少，这表明 gAP2 直接参与内吞作用和囊泡运输的机制不同。
