Bartles J R, Zheng L, Li A, Wierda A, Chen B
Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611, USA.
J Cell Biol. 1998 Oct 5;143(1):107-19. doi: 10.1083/jcb.143.1.107.
An approximately 30-kD isoform of the actin-binding/ bundling protein espin has been discovered in the brush borders of absorptive epithelial cells in rat intestine and kidney. Small espin is identical in sequence to the COOH terminus of the larger ( approximately 110-kD) espin isoform identified in the actin bundles of Sertoli cell-spermatid junctional plaques (Bartles, J.R., A. Wierda, and L. Zheng. 1996. J. Cell Sci. 109:1229-1239), but it contains two unique peptides at its NH2 terminus. Small espin was localized to the parallel actin bundles of brush border microvilli, resisted extraction with Triton X-100, and accumulated in the brush border during enterocyte differentiation/migration along the crypt-villus axis in adults. In transfected BHK fibroblasts, green fluorescent protein-small espin decorated F-actin-containing fibers and appeared to elicit their accumulation and/or bundling. Recombinant small espin bound to skeletal muscle and nonmuscle F-actin with high affinity (Kd = 150 and 50 nM) and cross-linked the filaments into bundles. Sedimentation, gel filtration, and circular dichroism analyses suggested that recombinant small espin was a monomer with an asymmetrical shape and a high percentage of alpha-helix. Deletion mutagenesis suggested that small espin contained two actin-binding sites in its COOH-terminal 116-amino acid peptide and that the NH2-terminal half of its forked homology peptide was necessary for bundling activity.
在大鼠肠道和肾脏的吸收性上皮细胞刷状缘中发现了一种肌动蛋白结合/成束蛋白espin的约30-kD同工型。小espin在序列上与在支持细胞-精子细胞连接斑的肌动蛋白束中鉴定出的较大（约110-kD）espin同工型的COOH末端相同（Bartles，J.R.，A. Wierda，和L. Zheng. 1996. J. Cell Sci. 109:1229-1239），但它在其NH2末端含有两个独特的肽段。小espin定位于刷状缘微绒毛的平行肌动蛋白束，抵抗Triton X-100的提取，并在成年动物中肠上皮细胞沿隐窝-绒毛轴分化/迁移过程中在刷状缘积累。在转染的BHK成纤维细胞中，绿色荧光蛋白-小espin装饰含F-肌动蛋白的纤维，并似乎引发它们的积累和/或成束。重组小espin以高亲和力（Kd = 150和50 nM）结合骨骼肌和非肌肉F-肌动蛋白，并将细丝交联成束。沉降、凝胶过滤和圆二色性分析表明，重组小espin是一种具有不对称形状和高比例α-螺旋的单体。缺失诱变表明，小espin在其COOH末端116个氨基酸肽段中含有两个肌动蛋白结合位点，并且其叉状同源肽的NH2末端一半对于成束活性是必需的。
