Department of Cell Biology and Anatomy, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo, 113-0033, Japan.
Department of Physics and Structural Biology Research Center, Chikusa-ku, Nagoya University, Nagoya, 464-8602, Japan.
Nat Commun. 2019 Mar 8;10(1):1143. doi: 10.1038/s41467-019-09051-x.
Motile cilia are microtubule-based organelles that play important roles in most eukaryotes. Although axonemal microtubules are sufficiently stable to withstand their beating motion, it remains unknown how they are stabilized while serving as tracks for axonemal dyneins. To address this question, we have identified two uncharacterized proteins, FAP45 and FAP52, as microtubule inner proteins (MIPs) in Chlamydomonas. These proteins are conserved among eukaryotes with motile cilia. Using cryo-electron tomography (cryo-ET) and high-speed atomic force microscopy (HS-AFM), we show that lack of these proteins leads to a loss of inner protrusions in B-tubules and less stable microtubules. These protrusions are located near the inner junctions of doublet microtubules and lack of both FAP52 and a known inner junction protein FAP20 results in detachment of the B-tubule from the A-tubule, as well as flagellar shortening. These results demonstrate that FAP45 and FAP52 bind to the inside of microtubules and stabilize ciliary axonemes.
纤毛是一种基于微管的细胞器，在大多数真核生物中发挥着重要作用。尽管轴丝微管足够稳定，可以承受其运动，但它们如何在作为轴丝动力蛋白的轨道的同时保持稳定仍然未知。为了解决这个问题，我们在衣藻中鉴定了两个未被描述的蛋白质，FAP45 和 FAP52，作为微管内蛋白（MIP）。这些蛋白质在具有运动纤毛的真核生物中是保守的。使用冷冻电镜断层扫描（cryo-ET）和高速原子力显微镜（HS-AFM），我们表明缺乏这些蛋白质会导致 B-微管内突起的丧失和微管稳定性降低。这些突起位于双微管的内连接附近，缺乏 FAP52 和已知的内连接蛋白 FAP20 会导致 B-微管从 A-微管上脱离，以及鞭毛缩短。这些结果表明 FAP45 和 FAP52 结合到微管的内部并稳定纤毛轴丝。
