Essential component of the mitotic spindle required for faithful chromosome segregation and progression into anaphase. Promotes the metaphase-to-anaphase transition and is required for chromosome alignment, normal timing of sister chromatid segregation, and maintenance of spindle pole architecture. The astrin (SPAG5)-kinastrin (SKAP) complex promotes stable microtubule-kinetochore attachments. Required for kinetochore oscillations and dynamics of microtubule plus-ends during live cell mitosis, possibly by forming a link between spindle microtubule plus-ends and mitotic chromosomes to achieve faithful cell division. Part of an astrin (SPAG5)-kinastrin (SKAP) complex containing KNSTRN, SPAG5, PLK1, DYNLL1 and SGO2 (By similarity). Interacts with SPAG5 (By similarity). Directly binds to microtubules, although at relatively low affinity (By similarity). Interacts with CENPE; this interaction greatly favors microtubule-binding (By similarity). Interacts with DSN1/MIS13; leading to localization to kinetochores (By similarity). Interacts with MAPRE1/EB1; leading to localization to the microtubule plus ends (By similarity). Interacts with PRPF19 (By similarity). Interacts with DYNLL1 (By similarity). Interacts with MAP4 (By similarity). Colocalizes with microtubules around centrosomes in prophase and with the mitotic spindle at prometaphase and metaphase. From late prometaphase to anaphase, is highly concentrated on kinetochores. Located at the kinetochore-microtubule interface. The astrin (SPAG5)-kinastrin (SKAP) complex localizes to the microtubule plus ends. The coiled coil regions mediate binding to kinetochores.