Structure and assembly of the A-C linker connecting microtubule triplets in centrioles

Centriole assembly involves the coordination of centriolar modules. One module is the A-C linker, an enigmatic protein assembly connecting the A-microtubule of one microtubule triplet to the C-microtubule of the neighboring triplet. Here, we integrated biochemistry, multiscale cryo-electron microscopy, and AlphaFold modeling to investigate the architecture of the centriole. Using an improved centriole isolation method, we determined the structure of the A-C linker bound to microtubule triplets, which revealed how the A-C linker cross-links microtubules and integrates with the B-C junction. We found marked changes in the structure and composition of the A-C linker that correlate with the presence of other centriolar modules, including the pinhead, cartwheel, and inner scaffold. Our findings show that the A-C linker is a highly integrated component of the centriole whose polymorphism may orchestrate the assembly of spatially distinct centriolar modules, and provide a framework for dissecting the biology of centrioles.