Nieset J E, Sacco-Bubulya P A, Sadler T M, Johnson K R, Wheelock M J
Department of Biology, University of Toledo, Toledo, OH 43606, USA.
J Cell Sci. 2000 May;113 ( Pt 10):1737-45. doi: 10.1242/jcs.113.10.1737.
beta-catenin and plakoglobin are members of the armadillo family of proteins and were first identified as components of intercellular adhering junctions. In the adherens junction beta-catenin and plakoglobin serve to link classical cadherins to the actin-based cytoskeleton. In the desmosome plakoglobin links the desmosomal cadherins, the desmogleins and the desmocollins, to the intermediate filament cytoskeleton. beta-catenin is not a component of the desmosome. Previously we have shown that the central armadillo repeat region of plakoglobin is the site for desmosomal cadherin binding. We hypothesized that the unique amino- and/or carboxyl-terminal ends of beta-catenin may regulate its exclusion from the desmosomal plaque. To test this hypothesis we used chimeras between beta-catenin and plakoglobin to identify domain(s) that modulate association with desmoglein 2. Chimeric constructs, each capable of associating with classical cadherins, were assayed for association with the desmosomal cadherin desmoglein 2. Addition of either the N- or C-terminal tail of beta-catenin to the armadillo repeats of plakoglobin did not interfere with desmoglein 2 association. However, when both beta-catenin amino terminus and carboxyl terminus were added to the plakoglobin armadillo repeats, association with desmoglein 2 was diminished. Removal of the first 26 amino acids from this construct restored association. We show evidence for direct protein-protein interactions between the amino- and carboxyl-terminal tails of beta-catenin and propose that a sequence in the first 26 amino acids of beta-catenin along with its carboxyl-terminal tail decrease its affinity for desmoglein and prevent its inclusion in the desmosome.
β-连环蛋白和桥粒斑珠蛋白是犰狳蛋白家族的成员，最初被鉴定为细胞间黏附连接的组成成分。在黏附连接中，β-连环蛋白和桥粒斑珠蛋白用于将经典钙黏蛋白与基于肌动蛋白的细胞骨架相连。在桥粒中，桥粒斑珠蛋白将桥粒钙黏蛋白、桥粒芯糖蛋白和桥粒胶蛋白与中间丝细胞骨架相连。β-连环蛋白不是桥粒的组成成分。此前我们已表明，桥粒斑珠蛋白的中央犰狳重复区域是桥粒钙黏蛋白结合位点。我们推测，β-连环蛋白独特的氨基端和/或羧基端可能调节其被排除在桥粒斑之外。为验证这一假设，我们使用β-连环蛋白和桥粒斑珠蛋白之间的嵌合体来鉴定调节与桥粒芯糖蛋白2结合的结构域。对每个能够与经典钙黏蛋白结合的嵌合构建体进行与桥粒钙黏蛋白桥粒芯糖蛋白2结合的检测。将β-连环蛋白的氨基端或羧基端添加到桥粒斑珠蛋白的犰狳重复序列中，均不影响与桥粒芯糖蛋白2的结合。然而，当将β-连环蛋白的氨基端和羧基端都添加到桥粒斑珠蛋白的犰狳重复序列中时，与桥粒芯糖蛋白2的结合减少。从该构建体中去除前26个氨基酸可恢复结合。我们展示了β-连环蛋白的氨基端和羧基端之间直接蛋白质-蛋白质相互作用的证据，并提出β-连环蛋白前26个氨基酸中的一个序列及其羧基端会降低其对桥粒芯糖蛋白的亲和力，并阻止其被纳入桥粒。
