Department of Bioengineering, McGill University, Montreal, Quebec, Canada.
Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont, USA.
J Biol Chem. 2024 Jun;300(6):107323. doi: 10.1016/j.jbc.2024.107323. Epub 2024 Apr 25.
Organelles and vesicular cargoes are transported by teams of kinesin and dynein motors along microtubules. We isolated endocytic organelles from cells at different stages of maturation and reconstituted their motility along microtubules in vitro. We asked how the sets of motors transporting a cargo determine its motility and response to the microtubule-associated protein tau. Here, we find that phagosomes move in both directions along microtubules, but the directional bias changes during maturation. Early phagosomes exhibit retrograde-biased transport while late phagosomes are directionally unbiased. Correspondingly, early and late phagosomes are bound by different numbers and combinations of kinesins-1, -2, -3, and dynein. Tau stabilizes microtubules and directs transport within neurons. While single-molecule studies show that tau differentially regulates the motility of kinesins and dynein in vitro, less is known about its role in modulating the trafficking of endogenous cargoes transported by their native teams of motors. Previous studies showed that tau preferentially inhibits kinesin motors, which biases late phagosome transport towards the microtubule minus-end. Here, we show that tau strongly inhibits long-range, dynein-mediated motility of early phagosomes. Tau reduces forces generated by teams of dynein motors on early phagosomes and accelerates dynein unbinding under load. Thus, cargoes differentially respond to tau, where dynein complexes on early phagosomes are more sensitive to tau inhibition than those on late phagosomes. Mathematical modeling further explains how small changes in the number of kinesins and dynein on cargoes impact the net directionality but also that cargoes with different sets of motors respond differently to tau.
细胞器和囊泡货物沿着微管由肌球蛋白和动力蛋白马达组成的团队运输。我们从不同成熟阶段的细胞中分离出内吞细胞器，并在体外重建它们沿微管的运动。我们想知道运输货物的马达组如何决定其运动和对微管相关蛋白 tau 的反应。在这里，我们发现吞噬体可以沿微管双向运动，但在成熟过程中定向偏差会发生变化。早期吞噬体表现出逆行偏向运输，而晚期吞噬体则没有定向。相应地，早期和晚期吞噬体被不同数量和组合的肌球蛋白-1、-2、-3 和动力蛋白结合。Tau 稳定微管并在神经元内指导运输。虽然单分子研究表明 tau 可在体外差异调节肌球蛋白和动力蛋白的运动，但对其在调节内源性货物运输中的作用知之甚少，这些货物是由其天然的马达组运输的。先前的研究表明 tau 优先抑制肌球蛋白马达，这使晚期吞噬体的运输偏向微管的负端。在这里，我们表明 tau 强烈抑制早期吞噬体的长程、动力蛋白介导的运动。Tau 降低了早期吞噬体上的动力蛋白马达产生的力，并在负载下加速动力蛋白的解结合。因此，货物对 tau 的反应不同，早期吞噬体上的 dynein 复合物对 tau 抑制的敏感性高于晚期吞噬体上的 dynein 复合物。数学模型进一步解释了货物上肌球蛋白和动力蛋白数量的微小变化如何影响净方向，但也解释了具有不同马达组的货物对 tau 的反应不同。
