Insights into the structure and function of ciliary and flagellar doublet microtubules: tektins, Ca2+-binding proteins and stable protofilaments [Cell Biology]

May 2nd, 2014 by Linck, R., Fu, X., Lin, J., Ouch, C., Schefter, A., Steffen, W., Warren, P., Nicastro, D.

Cilia and flagella are conserved, motile, sensory cell organelles involved in signal transduction and human disease. Their scaffold consists of a 9-fold array of remarkably stable doublet microtubules (DMTs), along which motor proteins transmit force for ciliary motility and intraflagellar transport. DMTs possess Ribbons of 3-4 hyper-stable protofilaments whose location, organization and specialized functions have been elusive. We performed a comprehensive analysis of the distribution and structural arrangements of Ribbon proteins from sea urchin sperm flagella, using quantitative immuno-biochemistry, proteomics, and immuno-cryo-electron microscopy and tomography. Isolated Ribbons contain acetylated-α-tubulin, β-tubulin, conserved protein Rib45, >95% of the axonemal tektins, and >95% of the calcium-binding proteins, Rib74 and Rib85.5, whose human homologues are related to the cause of juvenile myoclonic epilepsy. DMTs contain only one type of Ribbon, corresponding to protofilaments A11-12-13-1 of the A-tubule. Rib74 and Rib85.5 are associated with the Ribbon in the lumen of the A-tubule. Ribbons contain a single, ~5-nm wide filament, composed of equimolar tektins A, B and C, which interact with the nexin-dynein regulatory complex. A summary of findings is presented, and the functions of Ribbon proteins are discussed in terms of the assembly and stability of DMTs, ciliary motility and other microtubule systems.
  • Posted in Journal of Biological Chemistry, Publications
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