FAP206 is a microtubule-docking adapter for ciliary radial spoke 2 and dynein c.
Bottom Line: A knockout of the conserved ciliary protein FAP206 in the ciliate Tetrahymena resulted in slow cell motility.Occasionally, RS2 assembled but lacked both the front prong of its microtubule base and dynein c, whose tail is attached to the front prong.Overexpressed GFP-FAP206 decorated nonciliary microtubules in vivo.
Affiliation: Department of Cellular Biology, University of Georgia, Athens, GA 30602.Show MeSH
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Mentions: Previous biochemical and genetic studies linked FAP206 to the 96-nm outer doublet repeat (Lin et al., 2011; Gupta et al., 2012). We used cryo–electron tomography and subtomogram averaging to compare the high-resolution three-dimensional (3D) structure of the 96-nm repeat between the wild-type and FAP206-KO axonemes. We reconstructed cryotomograms of 10 wild-type and 7 FAP206-KO axonemes and averaged 1300 and 800 axonemal repeats, respectively. The most striking difference in the subtomogram averages of all repeats is the absence of the middle radial spoke RS2 and its closely associated IDA, dynein c, in the FAP206-KO axonemes (Figure 2 and Supplemental Movies S4 and S5). In the wild-type 96-nm repeat, the RS2 base is attached to the A-tubule by three contacts: the front, back, and side prongs (Figure 2, C, D, H, and K). The front and back prongs (red and yellow in Figure 2, respectively) resemble the corresponding structures in Chlamydomonas (Barber et al., 2012; Lin et al., 2012), whereas the side prong (light blue in Figure 2) is, so far, unique to RS2 of Tetrahymena. In the axonemal repeat of FAP206-KO, the front and back prong, of RS2 are absent, whereas the side prong remains (Figure 2, E, F, J, and L, and Supplemental Movie S6). We conclude that the base of the Tetrahymena RS2 attaches to the microtubule with three prongs, and the assembly of two of these prongs (front and back) depends on FAP206.
Affiliation: Department of Cellular Biology, University of Georgia, Athens, GA 30602.