Chen Xuejun, Molino Caitlyn, Liu Li, Gumbiner Barry M
Department of Cell Biology, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908, USA.
J Biol Chem. 2007 Nov 2;282(44):32128-37. doi: 10.1074/jbc.M705337200. Epub 2007 Sep 6.
Protocadherins have been shown to regulate cell adhesion, cell migration, cell survival, and tissue morphogenesis in the embryo and the central nervous system, but little is known about the mechanism of protocadherin function. We previously showed that Xenopus paraxial protocadherin (PAPC) mediates cell sorting and morphogenesis by down-regulating the adhesion activity of a classical cadherin, C-cadherin. Classical cadherins function by forming lateral dimers that are necessary for their adhesive function. However, it is not known whether oligomerization also plays a role in protocadherin function. We show here that PAPC forms oligomers that are stabilized by disulfide bonds formed between conserved Cys residues in the extracellular domain. Disruption of these disulfide bonds by dithiothreitol or mutation of the conserved cysteines results in defects in oligomerization, post-translational modification, trafficking to the cell surface and cell sorting function of PAPC. Furthermore, none of the residues in the cytoplasmic domain of PAPC is required for its cell sorting activity, whereas both the transmembrane domain and the extracellular domain are necessary. Therefore, protein oligomerization and/or protein interactions via the extracellular and transmembrane domains of PAPC are required for its cell sorting function.
原钙黏蛋白已被证明在胚胎和中枢神经系统中调节细胞黏附、细胞迁移、细胞存活及组织形态发生，但对原钙黏蛋白功能的机制了解甚少。我们之前表明，非洲爪蟾近轴原钙黏蛋白（PAPC）通过下调经典钙黏蛋白C-钙黏蛋白的黏附活性来介导细胞分选和形态发生。经典钙黏蛋白通过形成侧向二聚体发挥功能，这对其黏附功能是必需的。然而，尚不清楚寡聚化是否也在原钙黏蛋白功能中起作用。我们在此表明，PAPC形成寡聚体，这些寡聚体通过细胞外结构域中保守半胱氨酸残基之间形成的二硫键得以稳定。用二硫苏糖醇破坏这些二硫键或保守半胱氨酸的突变会导致PAPC寡聚化、翻译后修饰、转运至细胞表面及细胞分选功能出现缺陷。此外，PAPC胞质结构域中的任何残基对其细胞分选活性都不是必需的，而跨膜结构域和细胞外结构域都是必需的。因此，PAPC的细胞分选功能需要通过其细胞外和跨膜结构域进行蛋白质寡聚化和/或蛋白质相互作用。
