Structural Basis of the 9-Fold Symmetry of Centrioles

Summary

The centriole, and the related basal body, is an ancient organelle characterized by a universal 9-fold radial symmetry and is critical for generating cilia, flagella, and centrosomes. The mechanisms directing centriole formation are incompletely understood and represent a fundamental open question in biology. Here, we demonstrate that the centriolar protein SAS-6 forms rod-shaped homodimers that interact through their N-terminal domains to form oligomers. We establish that such oligomerization is essential for centriole formation in C. elegans and human cells. We further generate a structural model of the related protein Bld12p from C. reinhardtii, in which nine homodimers assemble into a ring from which nine coiled-coil rods radiate outward. Moreover, we demonstrate that recombinant Bld12p self-assembles into structures akin to the central hub of the cartwheel, which serves as a scaffold for centriole formation. Overall, our findings establish a structural basis for the universal 9-fold symmetry of centrioles.

Abstract

Graphical Abstract

Highlights

► Structural analysis of C. elegans centriolar protein SAS-6 reveals rod-shaped homodimers ► Higher-order oligomerization of SAS-6 homodimers is essential for centriole formation ► Nine homodimers of C. reinhardtii SAS-6 homolog Bld12p self-assemble into a ring ► Recombinant Bld12p forms structures akin to the hub and spokes of centriolar cartwheel