SAS-6 is a family of scaffold proteins required for normal centriole assembly. Elongated SAS-6 dimers can associate through their head domains to form the central hub and radiating spokes of the centriole cartwheel. This supplies a molecular route from interactions between proteins to the ninefold organization of a much larger organelle.
Daiju Kitagawa and colleagues combined protein structure determination, assembly experiments and cellular perturbations. Their model arranged nine dimers into a ring; electron microscopy of recombinant algal SAS-6 showed cartwheel-like assemblies, while mutations that impaired head-domain association also impaired centriole formation. The isolated structure alone would show a possible geometry; its agreement with assembly and perturbation experiments connects that geometry to function.[ref]
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