Journal Article

The Caenorhabditis elegans protein SAS-5 forms large oligomeric assemblies critical for centriole formation

Rogala, Kacper B, Dynes, Nicola J, Robinson, Carol V, Vakonakis, Ioannis, Deane, Charlotte M, Hatzopoulos, Georgios N, Yan, Jun, Pong, Sheng Kai, Gönczy, Pierre

2015

Overview

Centrioles are microtubule-based organelles crucial for cell division, sensing and motility. In Caenorhabditis elegans, the onset of centriole formation requires notably the proteins SAS-5 and SAS-6, which have functional equivalents across eukaryotic evolution. Whereas the molecular architecture of SAS-6 and its role in initiating centriole formation are well understood, the mechanisms by which SAS-5 and its relatives function is unclear. Here, we combine biophysical and structural analysis to uncover the architecture of SAS-5 and examine its functional implications in vivo. Our work reveals that two distinct self-associating domains are necessary to form higher-order oligomers of SAS-5: a trimeric coiled coil and a novel globular dimeric Implico domain. Disruption of either domain leads to centriole duplication failure in worm embryos, indicating that large SAS-5 assemblies are necessary for function in vivo. Most animal cells contain structures known as centrioles. Typically, a cell that is not dividing contains a pair of centrioles. But when a cell prepares to divide, the centrioles are duplicated. The two pairs of centrioles then organize the scaffolding that shares the genetic material equally between the newly formed cells at cell division. Centriole assembly is tightly regulated and abnormalities in this process can lead to developmental defects and cancer. Centrioles likely contain several hundred proteins, but only a few of these are strictly needed for centriole assembly. New centrioles usually assemble from a cartwheel-like arrangement of proteins, which includes a protein called SAS-6. In the worm Caenorhabditis elegans, SAS-6 associates with another protein called SAS-5. This interaction is essential for centrioles to form, but the reason behind this is not clearly understood. Now, Rogala et al. have used a range of techniques including X-ray crystallography, biophysics and studies of worm embryos to investigate the role of SAS-5 in C. elegans. These experiments revealed that SAS-5 proteins can interact with each other, via two regions of each protein termed a ‘coiled-coil’ and a previously unrecognized ‘Implico domain’. These regions drive the formation of assemblies that contain multiple SAS-5 proteins. Next, Rogala et al. asked whether SAS-5 assemblies are important for centriole duplication. Mutant worm embryos, in which SAS-5 proteins could not interact with one another, failed to form new centrioles. This resulted in defects with cell division. An independent study by Cottee, Muschalik et al. obtained similar results and found that the fruit fly equivalent of SAS-5, called Ana2, can also self-associate and this activity is required for centriole duplication. Further work is now needed to understand how SAS-5 and SAS-6 work with each other to form the initial framework at the core of centrioles.

• Publisher: eLife Sciences Publications Ltd,eLife Sciences Publications, Ltd
• Subject: Animals / Biophysics and Structural Biology / Caenorhabditis brenneri / Caenorhabditis briggsae / Caenorhabditis elegans / Caenorhabditis elegans - physiology / Caenorhabditis elegans Proteins - chemistry / Caenorhabditis elegans Proteins - genetics / Caenorhabditis elegans Proteins - metabolism / Caenorhabditis remanei / Caenorhabditis sinica / Caenorhabditis tropicalis / Cell Biology / Cell cycle / Cell Cycle Proteins - chemistry / Cell Cycle Proteins - genetics / Cell Cycle Proteins - metabolism / Cell Division / centriole / Centrioles / Centrioles - metabolism / crystallography / Crystallography, X-Ray / DNA Mutational Analysis / Embryos / Genomes / Kinases / Microscopy / Models, Molecular / Nematodes / Organelles / Protein Conformation / Protein Multimerization / Protein Structure, Tertiary / Proteins / structure / Symmetry / Zebrafish