Calpains are required for efficient microtubule detyrosination

Detyrosination is a major post-translational modification of microtubules (MT), which has significant impact on MT function in cell division, differentiation, growth, migration, polarity, and intracellular trafficking. Detyrosination of -tubulin occurs via the recently identified complex of vasohibin 1/2 (vash1/2) and small vasohibin binding protein (SVBP). However, there is still remaining detyrosinating activity in the absence of vash1/2/SVBP, and little is known about the regulation of detyrosination. Using cellular and cell-free assays we showed that the calcium-dependent proteases calpains 1 and 2 regulate MT detyrosination. We identified new calpain cleavage sites in the N-terminal disordered region of vash1 using in vitro proteolysis followed by mass spectrometry. However, this cleavage did not affect the detyrosination activity of vasohibin. In conclusion, the regulation of MT detyrosination by calpains occurs via another yet unknown tubulin carboxypeptidase. Importantly, calpains calcium dependency could allow a fine regulation of MT detyrosination. Thus, identifying the calpain-regulated pathway of MT detyrosination can be of major importance for several basic and clinical research and should be focused on in future studies. Summary StatementThe conventional calpains 1 and 2 play an important role in the regulation of microtubule detyrosination in a vasohibin independent way. Thus, they possibly control another still unknown tubulin carboxypeptidase.