InterPro domain: IPR042031

Spindle and kinetochore-associated protein 1 (SKA1) is a component of the SKA1 complex (consists of Ska1, Ska2, and Ska3/Rama1), a microtubule-binding subcomplex of the outer kinetochore that is essential for proper chromosome segregation [ 1 ]. It is required for timely anaphase onset during mitosis, when chromosomes undergo bipolar attachment on spindle microtubules leading to silencing of the spindle checkpoint [ 2 ]. The SKA1 complex is a direct component of the kinetochore-microtubule interface and directly associates with microtubules as oligomeric assemblies. The complex facilitates the processive movement of microspheres along a microtubule in a depolymerisation-coupled manner. SKA1 contains a microtubule-binding domain that interacts with tubulins using multiple contact sites that allow the Ska complex to bind microtubules in multiple modes [ 3 ].

This superfamily corresponds to the microtubule binding domain (MBD) in SKA1, spindle and kinetochore associated protein 1. Its structure is a variation of the winged helix domain which, in addition of the three helix-bundle and anti-parallel beta-sheets found in canonical winged-helix domains, it contains an extended helix (alphaB) as part of three helix bundle and an additional helix (alphaC) inserted between alphaB and betaA [ 4 ].

1. Timely anaphase onset requires a novel spindle and kinetochore complex comprising Ska1 and Ska2. EMBO J. 25, 5504-15
2. Structural and functional organization of the Ska complex, a key component of the kinetochore-microtubule interface. Mol. Cell 46, 274-86
3. Structural basis for microtubule recognition by the human kinetochore Ska complex. Nat Commun 5, 2964
4. The kinetochore-bound Ska1 complex tracks depolymerizing microtubules and binds to curved protofilaments. Dev. Cell 23, 968-80