Reconstitution of Tubulin Methylation by SETD2

Microtubules form one of the major components of the eukaryotic cytoskeleton. Assembled from evolutionarily conserved dimers of alpha and beta tubulin, microtubules are involved in a wide variety of cellular functions that range from transporting cargo to forming the mitotic spindle and creating primary cilia and flagella. Behaviour and function of microtubules are affected by their physical properties such as switching between growth and shrinkage (termed dynamic instability), and interacting with a range of microtubule associated proteins [1]. Even though microtubules are made of the same heterodimer building blocks, distinct populations localize in cells for specific functions including spatial organization, directional transport, and force generation. How microtubules achieve this functional diversity is at least in part driven by a “Tubulin Code” of tubulin isotypes and post-translational modifications (PTMs) (Figure 1). Analogous to the “Histone Code,” cells leverage the Tubulin Code to construct microtubule architecture with particular dynamical properties and specific functions [2]. The human genome encodes 8 alpha and 9 beta isotypes which have varying expression levels and functional properties. Most of these sequence differences in isotypes come from tubulin’s dynamic C-terminal tails (CTTs). Additionally, many known PTMs are found on these CTTs and have cellular localization and functional output in cells. To crack the PTM component of the Tubulin Code, both the modification and its writer need to be determined and characterized. So far, PTMs including, but not limited to, detyrosination, polyglutamylation, and acetylation are found enriched on specialized microtubule structures and their chemical writers and erasers have been identified [3] (Figure 1E).