Binds to the plus end of microtubules and regulates microtubule dynamics and microtubule organization. Acts as processive microtubule polymerase. Promotes cytoplasmic microtubule nucleation and elongation (PubMed:12176362, PubMed:18191222, PubMed:21282620). Plays a major role in organizing spindle poles (PubMed:23974040). In spindle formation protects kinetochore microtubules from depolymerization by kif2c and has an essential role in centrosomal microtubule assembly independently of kif2c activity. Contributes to centrosome integrity. Acts as component of the TACC3/ch-TOG/clathrin complex proposed to contribute to stabilization of kinetochore fibers of the mitotic spindle by acting as inter-microtubule bridge. Enhances the strength of NDC80 complex-mediated kinetochore-tip microtubule attachments (By similarity). Interacts with tacc3; two molecules of ckap5 interact with 1 molecule of tacc3 probably mediated by coiled coil domains forming a four-helix bundle. Interacts with tacc3 and clathrin forming the TACC3/ch-TOG/clathrin complex located at spindle inter-microtubules bridges. Interacts with ndc80; indicative for an association with the NDC80 comnplex (By similarity). The TOG (tumor overexpressed gene) domains are arranged in a N-terminal pentameric array with each domain composed of six (for the most part non-canonical) HEAT repeats forming a oblong paddle-like structure. Intra-HEAT loops are positioned along a face of the TOG domain and bind to a single alpha/beta-tubulin heterodimer. The TOG domains in the array seem to be structurally and functionally polarized. Differential functions may range from microtubule (MT) lattice binding and/or free tubulin heterodimer binding to potentiating stable incorporation of tubulin into the MT lattice. TOG 1 and TOG 2 are critical for microtubule polymerase activity. Belongs to the TOG/XMAP215 family.