Balabanian Linda, Berger Christopher L, Hendricks Adam G
Department of Bioengineering, McGill University, Montreal, Québec, Canada.
Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont.
Biophys J. 2017 Oct 3;113(7):1551-1560. doi: 10.1016/j.bpj.2017.08.009.
The motor proteins kinesin and dynein transport organelles, mRNA, proteins, and signaling molecules along the microtubule cytoskeleton. In addition to serving as tracks for transport, the microtubule cytoskeleton directs intracellular trafficking by regulating the activity of motor proteins through the organization of the filament network, microtubule-associated proteins, and tubulin posttranslational modifications. However, it is not well understood how these factors influence motor motility, and in vitro assays and live cell observations often produce disparate results. To systematically examine the factors that contribute to cytoskeleton-based regulation of motor protein motility, we extracted intact microtubule networks from cells and tracked the motility of single fluorescently labeled motor proteins on these cytoskeletons. We find that tubulin acetylation alone does not directly affect kinesin-1 motility. However, acetylated microtubules are predominantly bundled, and bundling enhances kinesin run lengths and provides a greater number of available kinesin binding sites. The neuronal MAP tau is also not sensitive to tubulin acetylation, but enriches preferentially on highly curved regions of microtubules where it strongly inhibits kinesin motility. Taken together, these results suggest that the organization of the microtubule network is a key contributor to the regulation of motor-based transport.
驱动蛋白和动力蛋白这两种运动蛋白沿着微管细胞骨架运输细胞器、信使核糖核酸、蛋白质和信号分子。微管细胞骨架除了作为运输轨道外，还通过细丝网络的组织、微管相关蛋白和微管蛋白的翻译后修饰来调节运动蛋白的活性，从而指导细胞内运输。然而，目前尚不清楚这些因素如何影响运动蛋白的运动能力，体外试验和活细胞观察往往会产生不同的结果。为了系统地研究有助于基于细胞骨架调节运动蛋白运动能力的因素，我们从细胞中提取完整的微管网络，并在这些细胞骨架上追踪单个荧光标记运动蛋白的运动。我们发现，仅微管蛋白乙酰化并不直接影响驱动蛋白-1的运动能力。然而，乙酰化微管主要是成束的，成束会增加驱动蛋白的运行长度，并提供更多可用的驱动蛋白结合位点。神经元微管相关蛋白tau对微管蛋白乙酰化也不敏感，但优先富集在微管的高度弯曲区域，在那里它强烈抑制驱动蛋白的运动。综上所述，这些结果表明微管网络的组织是基于运动蛋白的运输调节的关键因素。
