Structural organization of the C1b projection within the ciliary central apparatus

UMMS Affiliation

Division of Cell Biology and Imaging, Department of Radiology

Publication Date


Document Type



Amino Acids, Peptides, and Proteins | Cell Biology | Cellular and Molecular Physiology


Motile cilia have a '9+2' structure containing nine doublet microtubules and a central apparatus (CA) composed of two singlet microtubules with associated projections. The CA plays crucial roles in regulating ciliary motility. Defects in CA assembly or function usually result in motility-impaired or paralyzed cilia, which in humans causes disease. Despite their importance, the protein composition and functions of most CA projections remain largely unknown. Here, we combined genetic, proteomic and cryo-electron tomographic approaches to compare the CA of wild-type Chlamydomonas reinhardtii with those of three CA mutants. Our results show that two proteins, FAP42 and FAP246, are localized to the L-shaped C1b projection of the CA, where they interact with the candidate CA protein FAP413. FAP42 is a large protein that forms the peripheral 'beam' of the C1b projection, and the FAP246-FAP413 subcomplex serves as the 'bracket' between the beam (FAP42) and the C1b 'pillar' that attaches the projection to the C1 microtubule. The FAP246-FAP413-FAP42 complex is essential for stable assembly of the C1b, C1f and C2b projections, and loss of these proteins leads to ciliary motility defects.


Axoneme, Central pair complex, Cryo-electron tomography, Flagella, Subtomogram averaging

DOI of Published Version



Cai K, Zhao Y, Zhao L, Phan N, Hou Y, Cheng X, Witman GB, Nicastro D. Structural organization of the C1b projection within the ciliary central apparatus. J Cell Sci. 2021 Nov 1;134(21):jcs254227. doi: 10.1242/jcs.254227. Epub 2021 Nov 10. PMID: 34651179; PMCID: PMC8627600. Link to article on publisher's site

Journal/Book/Conference Title

Journal of cell science

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