Center for Lignocellulose Structure and Formation, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Plant Physiol. 2013 Sep;163(1):150-60. doi: 10.1104/pp.113.221234. Epub 2013 Jul 10.
Clathrin-mediated endocytosis (CME) is the best-characterized type of endocytosis in eukaryotic cells. Plants appear to possess all of the molecular components necessary to carry out CME; however, functional characterization of the components is still in its infancy. A yeast two-hybrid screen identified μ2 as a putative interaction partner of CELLULOSE SYNTHASE6 (CESA6). Arabidopsis (Arabidopsis thaliana) μ2 is homologous to the medium subunit 2 of the mammalian ADAPTOR PROTEIN COMPLEX2 (AP2). In mammals, the AP2 complex acts as the central hub of CME by docking to the plasma membrane while concomitantly recruiting cargo proteins, clathrin triskelia, and accessory proteins to the sites of endocytosis. We confirmed that μ2 interacts with multiple CESA proteins through the μ-homology domain of μ2, which is involved in specific interactions with endocytic cargo proteins in mammals. Consistent with its role in mediating the endocytosis of cargos at the plasma membrane, μ2-YELLOW FLUORESCENT PROTEIN localized to transient foci at the plasma membrane, and loss of μ2 resulted in defects in bulk endocytosis. Furthermore, loss of μ2 led to increased accumulation of YELLOW FLUORESCENT PROTEIN-CESA6 particles at the plasma membrane. Our results suggest that CESA represents a new class of CME cargo proteins and that plant cells might regulate cellulose synthesis by controlling the abundance of active CESA complexes at the plasma membrane through CME.
网格蛋白介导的内吞作用（CME）是真核细胞中研究得最充分的内吞作用类型。植物似乎拥有进行 CME 所需的所有分子成分；然而，这些成分的功能特征描述仍处于起步阶段。酵母双杂交筛选鉴定出 μ2 是纤维素合酶 6（CESA6）的一个假定相互作用伙伴。拟南芥（Arabidopsis thaliana）μ2 与哺乳动物衔接蛋白复合物 2（AP2）的中等亚基 2 同源。在哺乳动物中，AP2 复合物通过与质膜结合而充当 CME 的中心枢纽，同时将货物蛋白、网格蛋白三聚体和辅助蛋白募集到内吞部位。我们通过 μ2 的 μ-同源结构域证实 μ2 与多个 CESA 蛋白相互作用，该结构域参与了哺乳动物中内吞货物蛋白的特异性相互作用。与它在介导质膜上货物内吞作用的作用一致，μ2-黄色荧光蛋白定位于质膜上的瞬时焦点，并且 μ2 的缺失导致批量内吞作用缺陷。此外，μ2 的缺失导致 YELLOW FLUORESCENT PROTEIN-CESA6 颗粒在质膜上的积累增加。我们的结果表明，CESA 代表了一类新的 CME 货物蛋白，并且植物细胞可能通过 CME 控制质膜上活性 CESA 复合物的丰度来调节纤维素合成。
