Katanin plays a crucial role in severe human diseases such as tauophaties or microcephaly [1-2]. It is a microtubule-severing enzyme that has the unique capacity to catalyse the removal of tubulin dimers from the interior of the microtubule lattice and thereby cut microtubules (MT) into short fragments. It is necessary for meiotic spindle assembly, determination of mitotic spindle length, severing at microtubule crossovers, and cell motility [3-4]. Katanin is known for decades; however, structural information is missing and the role of interaction partners in the regulation of katanin function is not fully understood.
Here we performed a detailed biophysical, structural and functional characterization of katanin alone and in complex with two binding partners, ASPM (abnormal spindle-like microcephaly-associated protein) and CAMSAP (calmodulin-regulated spectrin-associated protein). We identified minimal regions of CAMSAP and ASPM necessary and sufficient for the interaction with katanin. We characterized the complexes biophysically using mainly sedimentation velocity analytical centrifugation and solved the crystal structures of katanin, and the katanin/CAMSAP, katanin/ASPM complexes. Our work revealed that CAMSAP and ASPM compete for the same binding site on katanin and functional analysis showed that katanin/ASPM and katanin/CAMSAP form MT minus-end binding complexes, that play major roles in regulating MT dynamics.