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 Caenorhabditis elegans 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 Chlamydomonas reinhardtii also fully activated the kinesin-2 from worm, even though C. reinhardtii itself lacks a homodimeric kinesin-2 motor. The latter suggested that a motor activation mechanism similar to the C. elegans 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 Tetrahymena thermophila not only possesses a homodimeric kinesin-2 but that it also shares the same allosteric activation mechanism that we delineated in the C. elegans 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.

中文翻译：

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kinesin-2 的生理货物适配器充当进化保守的开锁器

细胞货物的特异性识别和有效运输到其正确的细胞内目的地是大多数真核细胞面临的基础设施挑战。这种非凡的行为是由受强大监管机制约束的加工马达蛋白完成的。第一级调节需要电机抑制自身活动的能力。这种自身抑制最终会因特定的货物结合而得到缓解。为了更好地了解货物在电机激活过程中的作用，我们从中剖析了纤毛同二聚体驱动蛋白 2 的激活机制秀丽隐杆线虫通过其生理货物。在功能重组分析中，我们确定了两种货物衔接蛋白，它们一起对于变构激活自抑制马达是必要且足够的。令人惊讶的是，来自单细胞绿藻的直系同源衔接蛋白莱茵衣藻也完全激活了来自蠕虫的驱动蛋白 2，即使莱茵衣藻本身缺乏同源二聚体驱动蛋白 2 马达。后者表明类似于秀丽隐杆线虫模型在后生动物进化之前就已经存在，并促使我们仔细检查其他进化上遥远的真核生物中预测的同源二聚体驱动蛋白 2 直系同源物。我们证明纤毛虫嗜热四膜虫不仅拥有同源二聚体驱动蛋白 2，而且还共享我们在秀丽隐杆线虫模型。我们的结果表明同源二聚体驱动蛋白 2 在鞭毛内转运 (IFT) 中的作用比之前认为的要重要得多，并且需要对远缘相关生物体进行进一步审查，以全面了解 IFT 过程及其演变。