Center for Protein Assemblies (CPA), Physics Department, E22, Technical University of Munich, Garching, 85748, Germany.
Institute of Physiological Chemistry, Faculty of Medicine Carl Gustav Carus, Technische Universität Dresden, Dresden, 01307, Germany.
Proc Natl Acad Sci U S A. 2022 Aug 16;119(33):e2109378119. doi: 10.1073/pnas.2109378119. Epub 2022 Aug 10.
Specific recognition of cellular cargo and efficient transport to its correct intracellular destination is an infrastructural challenge faced by most eukaryotic cells. This remarkable deed is accomplished by processive motor proteins that are subject to robust regulatory mechanisms. The first level of regulation entails the ability of the motor to suppress its own activity. This autoinhibition is eventually relieved by specific cargo binding. To better understand the role of the cargo during motor activation, we dissected the activation mechanism of the ciliary homodimeric kinesin-2 from by its physiological cargo. In functional reconstitution assays, we identified two cargo adaptor proteins that together are necessary and sufficient to allosterically activate the autoinhibited motor. Surprisingly, the orthologous adaptor proteins from the unicellular green algae also fully activated the kinesin-2 from worm, even though itself lacks a homodimeric kinesin-2 motor. The latter suggested that a motor activation mechanism similar to the model existed already well before metazoans evolved, and prompted us to scrutinize predicted homodimeric kinesin-2 orthologs in other evolutionarily distant eukaryotes. We show that the ciliate not only possesses a homodimeric kinesin-2 but that it also shares the same allosteric activation mechanism that we delineated in the model. Our results point to a much more fundamental role of homodimeric kinesin-2 in intraflagellar transport (IFT) than previously thought and warrant further scrutiny of distantly related organisms toward a comprehensive picture of the IFT process and its evolution.
大多数真核细胞都面临着一个基本的挑战，即如何特异性识别细胞内物质并将其高效运输到正确的细胞内目的地。这一非凡的任务是通过连续运动的马达蛋白来完成的，而马达蛋白受到强大的调控机制的制约。调控的第一步是使马达蛋白能够抑制自身的活性。这种自动抑制最终会被特定的货物结合所解除。为了更好地理解货物在马达蛋白激活过程中的作用，我们通过其生理货物来剖析纤毛同源二聚体 kinesin-2 从 到 的激活机制。在功能重建测定中，我们鉴定了两个货物衔接蛋白，它们共同是别构激活自动抑制马达所必需和充分的。令人惊讶的是，来自单细胞绿藻 的同源衔接蛋白也能完全激活来自线虫的 kinesin-2，尽管 本身缺乏同源二聚体 kinesin-2 马达。后者表明，一种类似于 的马达蛋白激活机制早在后生动物进化之前就已经存在了，这促使我们仔细研究其他进化距离较远的真核生物中预测的同源二聚体 kinesin-2 同源物。我们表明，纤毛生物 不仅拥有同源二聚体 kinesin-2，而且还共享我们在 模型中描绘的别构激活机制。我们的结果表明，同源二聚体 kinesin-2 在鞭毛内运输 (IFT) 中的作用比之前认为的更为基础，并且有必要对远缘相关的生物体进行进一步的研究，以全面了解 IFT 过程及其进化。
