Studies on the Molecular Mechanisms That Produces and Controls Flagellar and Ciliary Movements

本研究旨在阐明产生和控制鞭毛和纤毛运动的分子机制。鞭毛和纤毛的跳动是基于相邻微管之间的滑动运动，由动力臂驱动。通过对动力蛋白臂的结构和滑动运动特性的研究，我们得到了以下重要发现：1)多细胞生物的动力蛋白臂通常包含两条重链，而单细胞生物的动力蛋白臂通常包含三条重链；2)外臂动力蛋白的三个中间链具有参与核苷酸代谢的酶活性；3)内臂动力蛋白包含真肌动蛋白作为亚基；4)动力蛋白功能的活性可能通过核苷酸结合动力蛋白重链中的多个位点来调节；动力蛋白本身可能具有产生振荡运动的性质。6)外臂动力蛋白和内臂动力蛋白似乎具有不同的产力特性。关于纤毛和鞭毛运动的调节，我们研究了蛋白磷酸化和钙离子的作用。我们首先获得的证据表明，哺乳动物精子fagella的磷酸化调控位点位于其基部；在鞭毛基部的蛋白磷酸化似乎调节了鞭毛是否开始跳动。在纤毛草履虫中，磷酸化似乎调节了对钙的敏感性。因此，纤毛运动似乎是由钙离子和蛋白质磷酸化的协调调节。在跳动的海胆精子轴突中，微管滑动明显受钙离子的调控。然而，在无载荷条件下，微管的滑动速度不受钙的影响。因此，钙离子似乎通过调节活性动力蛋白臂的数量来调节力的产生。钙如何调节动力蛋白的活性仍然是一个重要的未来问题。

This research has been aimed at the elucidation of the molecular mechanism that generates and controls flagellar and ciliary movements. The beating of flagella and cilia is based on the sliding movement between adjacent microtubules, driven by dynein arms. Through examination of the structure of dynein arms and properties of the sliding movement, we obtained the following important findings : 1) Outer dynein arms in multicellular organisms always contain two heavy chains, whereas those in unicellular organisms have three heavy chains ; 2) The three intermediate chains in the outer arm dynein have enzyme activities involved in nucleotide metabolism ; 3) Inner arm dynein contains true actin as a subunit ; 4) The activity of dynein function may be regulated through nucleotide binding to multiple sites in the dynein heavy chain ; 5) Dynein itself may have a nature to produce oscillatory movements. 6) Outer arm dynein and inner arm dynein appears to have different properties of force production. Regarding the regulation of ciliary and flagellar movements, we examined the effect of protein phosphorylation and calcium ion. We first obtained evidence that the site of phosphorylation-based regulation in mammalian sperm fagella is located at their bases ; protein phosphorylation at the base appears to regulate whether the flagella initiate beating. In Paramecium cilia, Phosphorylation appears to modulate the sensitivity to calcium. Thus, ciliary movements appear to be regulated by the coordination of calcium ion and protein phosphorylation. In beating sea urchin sperm axonemes, microtuble sliding is apparently regulated by calcium ion. However, the velocity of microtubule sliding under load-free conditions is not affected by calcium. Thus, calcium ion appears to regulate the force generation, possibly by regulating the number of active dynein arms. How calcium regulates the activity of dynein remains an important future problem.