Cell Adhesion Laboratory, UF Scripps, Jupiter, FL 33458, USA.
Department of Dermatology, The Feinberg School of Medicine, Northwestern University, Chicago, IL 606112, USA.
Int J Mol Sci. 2023 May 29;24(11):9458. doi: 10.3390/ijms24119458.
Plakophilin-3 is a ubiquitously expressed protein found widely in epithelial cells and is a critical component of desmosomes. The plakophilin-3 carboxy-terminal domain harbors nine armadillo repeat motifs with largely unknown functions. Here, we report the 5 Å cryogenic electron microscopy (cryoEM) structure of the armadillo repeat motif domain of plakophilin-3, one of the smaller cryoEM structures reported to date. We find that this domain is a monomer or homodimer in solution. In addition, using an in vitro actin co-sedimentation assay, we show that the armadillo repeat domain of plakophilin-3 directly interacts with F-actin. This feature, through direct interactions with actin filaments, could be responsible for the observed association of extra-desmosomal plakophilin-3 with the actin cytoskeleton directly attached to the adherens junctions in A431 epithelial cells. Further, we demonstrate, through lipid binding analyses, that plakophilin-3 can effectively be recruited to the plasma membrane through phosphatidylinositol-4,5-bisphosphate-mediated interactions. Collectively, we report on novel properties of plakophilin-3, which may be conserved throughout the plakophilin protein family and may be behind the roles of these proteins in cell-cell adhesion.
桥粒斑蛋白-3 是一种广泛表达的蛋白,在大多数上皮细胞中广泛存在,是桥粒的关键组成部分。桥粒斑蛋白-3 的羧基末端结构域含有九个类角蛋白重复序列基元,其功能大多未知。在这里,我们报告了桥粒斑蛋白-3 的类角蛋白重复序列基元结构域的 5 Å 冷冻电镜(cryoEM)结构,这是迄今为止报道的较小的 cryoEM 结构之一。我们发现该结构域在溶液中为单体或同源二聚体。此外,通过体外肌动蛋白共沉淀测定,我们表明桥粒斑蛋白-3 的类角蛋白重复序列结构域直接与 F-肌动蛋白相互作用。这一特性,通过与肌动蛋白丝的直接相互作用,可能负责观察到桥粒斑蛋白-3 与上皮细胞 A431 中直接附着在黏着连接的肌动蛋白细胞骨架的额外桥粒外斑蛋白的关联。此外,我们通过脂质结合分析表明,桥粒斑蛋白-3 可以通过磷脂酰肌醇-4,5-二磷酸介导的相互作用有效地被募集到质膜上。总的来说,我们报告了桥粒斑蛋白-3 的新特性,这些特性可能在整个桥粒斑蛋白蛋白家族中保守,并可能是这些蛋白在细胞间黏附中发挥作用的原因。