Molecular interactions between tubulin tails and glutamylases reveal determinants of glutamylation patterns

Abstract

Posttranslational modifications of tubulin currently emerge as key regulators of microtubule functions. Polyglutamylation generates a variety of modification patterns that are essential for controlling microtubule functions in different cell types and organelles, and deregulation of these patterns has been linked to ciliopathies, cancer and neurodegeneration. How the different glutamylating enzymes determine precise modification patterns has so far remained elusive. Using computational modelling, molecular dynamics simulations and mutational analyses we now show how the carboxy‐terminal tails of tubulin bind into the active sites of glutamylases. Our models suggest that the glutamylation sites on α‐ and β‐tubulins are determined by the positioning of the tails within the catalytic pocket. Moreover, we found that the binding modes of α‐ and β‐tubulin tails are highly similar, implying that most enzymes could potentially modify both, α‐ and β‐tubulin. This supports a model in which the binding of the enzymes to the entire microtubule lattice, but not the specificity of the C‐terminal tubulin tails to their active sites, determines the catalytic specificities of glutamylases. image Glutamylation of tubulin gives rise to a variety of modification patterns, which control microtubule functions. To determine how glutamylase enzymes generate these different patterns, the authors have modeled the molecular interactions between glutamylases and their tubulin substrates. Tubulin glutamylases remodel their active site upon binding of their substrate—the tubulin tail—which themselves restructure in the process of binding. This suggests an induced‐fit model of enzyme dynamics. Preferential glutamylation sites within tubulin tails are determined by the positioning of the tails within the catalytic pocket of the enzyme. Interactions between the active site of glutamylases and the tubulin C‐terminal tails are not sufficient to determine preferences of glutamylases to α‐ or β‐tubulin. This suggests that interactions of these enzymes with the entire microtubule lattice are required to define this preference.