Hatzfeld M, Kristjansson G I, Plessmann U, Weber K
Max Planck Institute for Biophysical Chemistry, Department of Biochemistry, Goettingen, FRG.
J Cell Sci. 1994 Aug;107 ( Pt 8):2259-70. doi: 10.1242/jcs.107.8.2259.
Desmosomes are intercellular adhering junctions characteristic of epithelial cells. Several constitutive proteins--desmoplakin, plakoglobin and the transmembrane glycoproteins desmoglein and desmocollin--have been identified as fundamental constituents of desmosomes in all tissues. A number of additional and cell type-specific constituents also contribute to desmosomal plaque formation. Among these proteins is the band 6 polypeptide (B6P). This positively charged, non-glycosylated protein is a major constituent of the plaque in stratified and complex glandular epithelia. Using an overlay assay we show that purified keratins bind in vitro to B6P. Thus B6P may play a role in ordering intermediate filament networks of adjacent epithelial cells. To characterize the structure of B6P in the desmosome we have isolated cDNA clones representing the entire coding sequence. The predicted amino acid sequence of human B6P shows strong sequence homology with a murine p120 protein, which is a substrate of protein tyrosine kinase receptors and of p60v-src. P120 and B6P show amino-terminal domains differing distinctly in length and sequence. These are followed in both proteins by 460 residues that display a series of imperfect repeats corresponding to the repeats in the cadherin binding proteins armadillo, plakoglobin and beta-catenin. Over this repeat region B6P and p120 share 33% sequence identity (54% similarity). These sequence characteristics define B6P as a novel member of the armadillo multigene family and raise the question of whether the structural proteins B6P, plakoglobin, beta-catenin and armadillo share some function. Since armadillo, plakoglobin, beta-catenin and p120 seem involved in signal transduction this may also hold for B6P. The amino-terminal region of B6P (residues 1 to 263) shows no significant homology to any known protein sequence. It may therefore be involved in unique functions of B6P.
桥粒是上皮细胞特有的细胞间黏附连接。几种组成蛋白——桥粒斑蛋白、桥粒珠蛋白以及跨膜糖蛋白桥粒芯糖蛋白和桥粒胶蛋白——已被确定为所有组织中桥粒的基本组成成分。许多其他的细胞类型特异性成分也有助于桥粒斑的形成。这些蛋白质中有6带多肽（B6P）。这种带正电荷的非糖基化蛋白是复层和复杂腺上皮中斑块的主要成分。通过覆盖分析，我们发现纯化的角蛋白在体外与B6P结合。因此，B6P可能在相邻上皮细胞的中间丝网络排列中发挥作用。为了表征桥粒中B6P的结构，我们分离了代表整个编码序列的cDNA克隆。人B6P的预测氨基酸序列与鼠p120蛋白具有很强的序列同源性，鼠p120蛋白是蛋白酪氨酸激酶受体和p60v-src的底物。P120和B6P的氨基末端结构域在长度和序列上明显不同。在这两种蛋白质中，这些结构域之后是460个残基，它们显示出一系列不完美的重复序列，与钙黏着蛋白结合蛋白犰狳、桥粒珠蛋白和β-连环蛋白中的重复序列相对应。在这个重复区域，B6P和p120共享33%的序列同一性（54%的相似性）。这些序列特征将B6P定义为犰狳多基因家族的一个新成员，并提出了结构蛋白B6P、桥粒珠蛋白、β-连环蛋白和犰狳是否具有某些共同功能的问题。由于犰狳、桥粒珠蛋白、β-连环蛋白和p120似乎参与信号转导，B6P可能也是如此。B6P的氨基末端区域（第1至263位残基）与任何已知蛋白质序列均无明显同源性。因此，它可能参与B6P的独特功能。
