Kinesin-14s are microtubule-based motor proteins that play important roles in mitotic spindle assembly [1]. Ncd-type kinesin-14s are a subset of kinesin-14 motors that exist as homodimers with an N-terminal microtubule-binding tail, a coiled-coil central stalk (central stalk), a neck, and two identical C-terminal motor domains. To date, no Ncd-type kinesin-14 has been found to naturally exhibit long-distance minus-end-directed processive motility on single microtubules as individual homodimers. Here, we show that GiKIN14a from Giardia intestinalis [2] is an unconventional Ncd-type kinesin-14 that uses its N-terminal microtubule-binding tail to achieve minus-end-directed processivity on single microtubules over micrometer distances as a homodimer. We further find that although truncation of the N-terminal tail greatly reduces GiKIN14a processivity, the resulting tailless construct GiKIN14a-Δtail is still a minimally processive motor and moves its center of mass via discrete 8-nm steps on the microtubule. In addition, full-length GiKIN14a has significantly higher stepping and ATP hydrolysis rates than does GiKIN14a-Δtail. Inserting a flexible polypeptide linker into the central stalk of full-length GiKIN14a nearly reduces its ATP hydrolysis rate to that of GiKIN14a-Δtail. Collectively, our results reveal that the N-terminal tail of GiKIN14a is a de facto dual regulator of motility and reinforce the notion of the central stalk as a key mechanical determinant of kinesin-14 motility [3].

Kinesin-14s 是基于微管的运动蛋白，在有丝分裂纺锤体组装中发挥重要作用 [1]。Ncd 型 kinesin-14s 是 kinesin-14 马达的一个子集，作为同型二聚体存在，具有 N 端微管结合尾、卷曲螺旋中央柄（中央柄）、颈部和两个相同的 C 端运动域. 迄今为止，尚未发现 Ncd 型驱动蛋白 14 在单个微管上作为单个同源二聚体自然地表现出长距离负端导向的持续运动。在这里，我们展示了来自肠道贾第鞭毛虫的GiKIN14a[2] 是一种非常规的 Ncd 型驱动蛋白 14，它使用其 N 端微管结合尾部作为同源二聚体在微米距离的单个微管上实现负端导向的持续合成。我们进一步发现，虽然 N 端尾部的截断大大降低了 GiKIN14a 的加工能力，但由此产生的无尾结构 GiKIN14a-Δtail 仍然是一个最小加工电机，并通过微管上的离散 8 nm 步长移动其质心。此外，全长 GiKIN14a 的步进和 ATP 水解速率明显高于 GiKIN14a-Δtail。将柔性多肽接头插入全长 GiKIN14a 的中央茎几乎将其 ATP 水解速率降低到 GiKIN14a-Δtail 的水解速率。总的来说，我们的结果表明 GiKIN14a 的 N 端尾部是事实上的 运动的双重调节剂，并强化了中央茎作为驱动蛋白 14 运动的关键机械决定因素的概念 [3]。