The distribution of mass in heteropolymer intermediate filaments assembled in vitro. Stem analysis of vimentin/desmin and bovine epidermal keratin.
The distribution of mass in heteropolymer intermediate filaments assembled in vitro. Stem analysis of vimentin/desmin and bovine epidermal keratin.
复制标题
体外组装的杂聚物中间丝的质量分布。
DOI：
--
复制
发表时间：
1983
影响因子：
4.8
通讯作者：
P. Steinert
中科院分区：
文献类型：
--
作者：
A. Steven;J. Hainfeld;B. Trus;J. Wall;P. Steinert
我们已经研究了质量分布在几种类型的中间丝（IF）组装在体外，通过分析扫描透射电子显微镜（STEM）的暗场模式成像的未染色标本。牛表皮角蛋白IF，这是专性杂聚物，因此，其特征在于，并与兼性杂聚物的波形蛋白和结蛋白，并与早期的观察均聚物波形蛋白IF。每种类型的IF的主要组分具有37千道尔顿/nm的线密度。在每种情况下也存在较小的多态性变体，线性密度分别约为25和48千道尔顿/nm。鉴于已知的亚基群众，这些结果是一致的命题，即至少有三个IF类型（牛表皮角蛋白，波形蛋白，结蛋白）是结构同源的。对于研究的每种类型的IF，在长IF或短IF的末端附近进行的测量往往具有较低的密度，这是密度最小的多态性变体的特征。这种形式可能代表一种前体“最小核心”结构，在这种意义上，原丝的最小聚集体足够稳定以允许伸长。在体外组装的过程中，这种形式将通过增加更多的蛋白质而在37千道尔顿/nm下成熟为正常的IF结构。我们还发现，从STEM图像测量的这些IF的投影宽度显着大于在以前的研究中通过传统的电子显微镜确定的相应直径。尽管常规技术常规产生的直径为7-11 nm的IF对比重金属染色，未染色的IF的STEM图像提供的估计值为15 +/- 1 nm的外径的主要密度类的每一个IF类型的研究和平均值为13.8和16.1 nm的较低密度和更密集的变种，分别。
We have studied the distribution of mass in several types of intermediate filaments (IF) assembled in vitro, by analyzing scanning transmission electron micrographs (STEM) of unstained specimens imaged in dark-field mode. Bovine epidermal keratin IF, which are obligate heteropolymers, were thus characterized and compared with facultative heteropolymers of vimentin and desmin and with earlier observations of homopolymer vimentin IF. The major components of each type of IF have linear densities of 37 kilodaltons/nm. Minor polymorphic variants are also present in each case, with linear densities of approximately 25 and 48 kilodaltons/nm, respectively. In view of the known subunit masses, these results are consistent with the proposition that at least three IF types (bovine epidermal keratin, vimentin, and desmin) are structurally homologous. For each type of IF studied, measurements taken near the ends of long IF or from short IF tend to have lower densities, characteristic of the least dense polymorphic variant. This form may represent a precursor "minimal core" structure in the sense of a minimal aggregate of protofilaments sufficiently stable to permit elongation. In the course of in vitro assembly, this form would be maturable to the normal IF structure at 37 kilodaltons/nm by the accretion of further protein. We also find the projected widths of these IF as measured from the STEM images to be significantly greater than the corresponding diameters determined in previous studies by conventional electron microscopy. Whereas the conventional techniques have routinely yielded diameters of 7-11 nm for IF contrasted by heavy metal staining, the STEM images of unstained IF provide estimates of 15 +/- 1 nm for the outer diameter of the major density class for each IF type studied and average values of 13.8 and 16.1 nm for the less dense and more dense variants, respectively.