Franke W W, Winter S, Grund C, Schmid E, Schiller D L, Jarasch E D
J Cell Biol. 1981 Jul;90(1):116-27. doi: 10.1083/jcb.90.1.116.
Epithelial cells of the small intestine, like those of other internal organs, contain intermediate-sized filaments immunologically related to epidermal prekeratin which are especially concentrated in the cell apex. Brush-order fractions were isolated from rat small intestine, and apical tonofilaments attached to desmosomal plaques and terminal web residues were prepared therefrom by extraction in high salt (1.5 M KCl) buffer and Triton X-100. The structure of these filaments was indistinguishable from that of epidermal tonofilaments and, as with epidermal prekeratin, filaments could be reconstituted from solubilized, denatured intestinal tonofilament protein. On SDS polyacrylamide gel electrophoresis of proteins of the extracted desmosome-tonofilament fractions, a number of typical brush-border proteins were absent or reduced, and enrichment of three major polypeptides of Mr 55,000, 48,000, and 40,000 was noted. On two-dimensional gel electrophoresis, the three enriched major polypeptides usually appeared as pairs of isoelectric variants, and the two smaller components (Mr 48,000, and 40,000) were relatively acidic (isoelectric pH values of 5.40 and below), compared to the Mr 55,000 protein which focused at pH values higher than 6.4. The tonofilament proteins were shown to be immunologically related to epidermal prekeratin by immunoreplica and blotting techniques using antibodies to bovine epidermal prekeratins. Similar major polypeptides were found in desmosome-attached tonofilaments from small intestine of mouse and cow. However, comparisons with epidermal tissues of cow and rat showed that all major polypeptides of intestinal tonofilaments were different from the major prekeratin polypeptides of epidermal tonofilaments. The results present the first analysis of a defined fraction of tonofilaments from a nonepidermal cell. The data indicate that structurally identical tonofilaments can be formed, in different types of cells, by different polypeptides of the cytokeratin family of proteins and that tonofilaments of various epithelia display tissue-specific patterns of their protein subunits.
小肠上皮细胞与其他内脏器官的上皮细胞一样，含有与表皮前角蛋白免疫相关的中等大小的细丝，这些细丝特别集中在细胞顶端。从大鼠小肠中分离出刷状缘部分，通过在高盐（1.5M KCl）缓冲液和Triton X-100中提取，从中制备附着在桥粒斑和终末网残留物上的顶端张力丝。这些细丝的结构与表皮张力丝的结构无法区分，并且与表皮前角蛋白一样，细丝可以由溶解、变性的肠张力丝蛋白重构而成。在提取的桥粒-张力丝部分的蛋白质的SDS聚丙烯酰胺凝胶电泳中，一些典型的刷状缘蛋白缺失或减少，并且注意到三种主要多肽（分子量分别为55,000、48,000和40,000）的富集。在二维凝胶电泳中，这三种富集的主要多肽通常表现为等电变体对，与聚焦在pH值高于6.4的55,000分子量的蛋白质相比，两个较小的组分（分子量48,000和40,000）相对呈酸性（等电pH值为5.40及以下）。通过使用针对牛表皮前角蛋白的抗体的免疫复型和印迹技术，显示张力丝蛋白与表皮前角蛋白免疫相关。在小鼠和牛小肠的桥粒附着张力丝中发现了类似的主要多肽。然而，与牛和大鼠的表皮组织比较表明，肠张力丝的所有主要多肽都与表皮张力丝的主要前角蛋白多肽不同。这些结果首次分析了来自非表皮细胞的特定部分的张力丝。数据表明，在不同类型的细胞中，细胞角蛋白家族的不同多肽可以形成结构相同的张力丝，并且各种上皮组织的张力丝显示出其蛋白质亚基的组织特异性模式。
