Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan;
EcoTopia Science Institute, Nagoya University, Chikusa, Nagoya 464-8602, Japan;
Proc Natl Acad Sci U S A. 2014 Jul 1;111(26):9461-6. doi: 10.1073/pnas.1403101111. Epub 2014 Jun 16.
Outer arm dynein (OAD) in cilia and flagella is bound to the outer doublet microtubules every 24 nm. Periodic binding of OADs at specific sites is important for efficient cilia/flagella beating; however, the molecular mechanism that specifies OAD arrangement remains elusive. Studies using the green alga Chlamydomonas reinhardtii have shown that the OAD-docking complex (ODA-DC), a heterotrimeric complex present at the OAD base, functions as the OAD docking site on the doublet. We find that the ODA-DC has an ellipsoidal shape ∼24 nm in length. In mutant axonemes that lack OAD but retain the ODA-DC, ODA-DC molecules are aligned in an end-to-end manner along the outer doublets. When flagella of a mutant lacking ODA-DCs are supplied with ODA-DCs upon gamete fusion, ODA-DC molecules first bind to the mutant axonemes in the proximal region, and the occupied region gradually extends toward the tip, followed by binding of OADs. This and other results indicate that a cooperative association of the ODA-DC underlies its function as the OAD-docking site and is the determinant of the 24-nm periodicity.
外臂动力蛋白 (OAD) 在纤毛和鞭毛中与外微管双联体每隔 24nm 结合一次。OAD 在特定部位的周期性结合对于有效的纤毛/鞭毛拍打很重要；然而，指定 OAD 排列的分子机制仍然难以捉摸。使用绿藻衣藻的研究表明，OAD docking 复合物 (ODA-DC)，一种存在于 OAD 基部的异三聚体复合物，作为双联体上的 OAD docking 位点发挥作用。我们发现 ODA-DC 呈长约 24nm 的椭圆形。在缺乏 OAD 但保留 ODA-DC 的突变轴丝中，ODA-DC 分子沿着外微管以端到端的方式对齐。当缺乏 ODA-DC 的突变体的鞭毛在配子融合时提供 ODA-DC 时，ODA-DC 分子首先结合到突变轴丝的近端区域，被占据的区域逐渐向尖端延伸，然后结合 OAD。这和其他结果表明，ODA-DC 的协同关联是其作为 OAD docking 位点的功能基础，也是 24nm 周期性的决定因素。
