EMBO Rep., published online 10 February 2012, doi:10.1038/embor.2012.1

Credit: F. SCHMITZBERGER AND S.C. HARRISON

Eukaryotic kinetochores are molecular machines composed of multimeric complexes that attach the chromosomes to microtubules during cell division. A linker complex that bridges the complexes associated with the chromosomes and microtubules is essential. Schmitzberger and Harrison now report the structure of the linker protein subcomplex Ctf19–Mcm21, which belongs to the larger linker complex COMA. The authors observed that each protein forms two folded α+β sandwiches, which belong to the family of RWD domains, connected by an α-helix of ∼40-Å length. The N-terminal α+β sandwiches form tight interprotein interactions, whereas the C-terminal ones protrude away from each other, forming a Y shape. The crystal structure and limited proteolysis showed that the N-terminal residues of both proteins are unstructured and do not interact with each other or with other proteins of the linker complex. Truncation experiments indicated that the double RWD domains of the Ctf19–Mcm21 subcomplex are necessary and sufficient to interact with the larger COMA complex. Comparisons of the RWD domains of Ctf19–Mcm21 proteins with those of other kinetochore proteins revealed several other examples of these structural modules, pointing to the importance of the RWD domains in kinetochore architecture.