Steinert P M, Marekov L N, Parry D A
Laboratory of Skin Biology, NIAMS, National Institutes of Health, Bethesda, Maryland 20892-2752, USA.
J Biol Chem. 1999 Jan 15;274(3):1657-66. doi: 10.1074/jbc.274.3.1657.
During neuronal development, a dynamic replacement mechanism occurs in which the type VI nestin and type III vimentin intermediate filament proteins are replaced by a series of type IV proteins beginning with alpha-internexin. We have explored molecular details of how the type III to type IV replacement process may occur. First, we have demonstrated by cross-linking experiments that bacterially expressed forms of alpha-internexin and vimentin form heterodimer molecules in vitro that assemble into copolymer intermediate filaments. We show using a urea disassembly assay that alpha-internexin molecules are likely to be more stable than those of vimentin. Second, by analyses of the induced cross-links, we have determined the axial lengths of alpha-internexin homodimer and alpha-internexin-vimentin heterodimer molecules and their modes of alignments in filaments. We report that these dimensions are the same as those reported earlier for vimentin homopolymer molecules and, by implication, are also the same for the other neuronal type IV proteins. These data suggest that during neuronal development, alpha-internexin molecules are readily assimilated onto the pre-existing vimentin cytoskeletal intermediate filament network because the axial lengths and axial alignments of their molecules are the same. Furthermore, the dynamic replacement process may be driven by a positive equilibrium due to the increased stability of the alpha-internexin network.
在神经元发育过程中，会发生一种动态替换机制，即VI型巢蛋白和III型波形蛋白中间丝蛋白被一系列IV型蛋白所取代，首先是α-互连蛋白。我们探讨了III型到IV型替换过程可能发生的分子细节。首先，我们通过交联实验证明，细菌表达形式的α-互连蛋白和波形蛋白在体外形成异二聚体分子，并组装成共聚物中间丝。我们使用尿素拆解试验表明，α-互连蛋白分子可能比波形蛋白分子更稳定。其次，通过对诱导交联的分析，我们确定了α-互连蛋白同二聚体和α-互连蛋白-波形蛋白异二聚体分子的轴向长度及其在丝中的排列方式。我们报告说，这些尺寸与先前报道的波形蛋白同聚物分子的尺寸相同，并且由此推断，其他神经元IV型蛋白的尺寸也相同。这些数据表明，在神经元发育过程中，α-互连蛋白分子很容易被整合到预先存在的波形蛋白细胞骨架中间丝网络中，因为它们分子的轴向长度和轴向排列是相同的。此外，由于α-互连蛋白网络稳定性的增加，动态替换过程可能由正平衡驱动。
