6 research outputs found
Tubulin lattice in cilia is in a stressed form regulated by microtubule inner proteins
Cilia, the hair-like protrusions that beat at high frequencies to propel a cell or move fluid around are composed of radially bundled doublet microtubules. In this study, we present a near-atomic resolution map of the Tetrahymena doublet microtubule by cryoelectron microscopy. The map demonstrates that the network of microtubule inner proteins weaves into the tubulin lattice and forms an inner sheath. From mass spectrometry data and de novo modeling, we identified Rib43a proteins as the filamentous microtubule inner proteins in the protofilament ribbon region. The Rib43a–tubulin interaction leads to an elongated tubulin dimer distance every 2 dimers. In addition, the tubulin lattice structure with missing microtubule inner proteins (MIPs) by sarkosyl treatment shows significant longitudinal compaction and lateral angle change between protofilaments. These results are evidence that the MIPs directly affect and stabilize the tubulin lattice. It suggests that the doublet microtubule is an intrinsically stressed filament and that this stress could be manipulated in the regulation of ciliary waveforms
The inner junction complex of the cilia is an interaction hub that involves tubulin post-translational modifications
The inner junction complex of the cilia is an interaction hub that involves tubulin post-translational modifications
Microtubules are cytoskeletal structures involved in stability, transport and
organization in the cell. The building blocks, the a- and b-tubulin heterodimers, form protofilaments
that associate laterally into the hollow microtubule. Microtubule also exists as highly stable doublet
microtubules in the cilia where stability is needed for ciliary beating and function. The doublet
microtubule maintains its stability through interactions at its inner and outer junctions where its A-
and B-tubules meet. Here, using cryo-electron microscopy, bioinformatics and mass spectrometry
of the doublets of Chlamydomonas reinhardtii and Tetrahymena thermophila, we identified two
new inner junction proteins, FAP276 and FAP106, and an inner junction-associated protein,
FAP126, thus presenting the complete answer to the inner junction identity and localization. Our
structural study of the doublets shows that the inner junction serves as an interaction hub that
involves tubulin post-translational modifications. These interactions contribute to the stability of the
doublet and hence, normal ciliary motility