Abstract
Cilia and flagella are slender projections found on most eukaryotic cells including unicellular organisms such as Chlamydomonas, Trypanosoma and Tetrahymena, where they serve motility and signaling functions. The cilium is a large molecular machine consisting of hundreds of different proteins that are trafficked into the organelle to organize a repetitive microtubule-based axoneme. Several recent studies took advantage of improved cryo-EM methodology to unravel the high-resolution structures of ciliary complexes. These include the recently reported purification and structure determination of axonemal doublet microtubules from the green algae Chlamydomonas reinhardtii, which allows for the modeling of more than 30 associated protein factors to provide deep molecular insight into the architecture and repetitive nature of doublet microtubules. In addition, we will review several recent contributions that dissect the structure and function of ciliary trafficking complexes that ferry structural and signaling components between the cell body and the cilium organelle.
Highlights
Microbial cells often utilize cellular structures known as flagella to swim in aqueous environments
Flagellumdriven motility can occur in response to chemical stimuli or in response to a light source and allows cells to swim towards beneficial environments
Significant progress in understanding doublet MT (DMT) came with a recent publication where the authors made use of technical advances in cryo electron microscopy [33, 34] to obtain high-resolution single-particle reconstructions of DMTs, which allowed for the structural modelling of 33 MT inner proteins (MIPs) associated with the lumen of DMTs [35]
Summary
Microbial cells often utilize cellular structures known as flagella to swim in aqueous environments. Motile cilia are structurally different from primary cilia given that they harbour inner and outer dynein arms, which are macromolecular motor complexes that associate with DMTs and hydrolyse ATP to power the ciliary beat required for swimming [16,17,18,19] (Figure 1b).
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