Analysis of DVL3 polyglutamylation using Q-TOF

Polyglutamylation is a reversible post-translational modification initially discovered on tubulin. In eukaryotes, polyglutamylation is catalyzed by enzymes from the tubulin tyrosine ligase-like (TTLL) family, which show substrate and reaction specificities that are so far mostly explored on tubulin. By contrast, little is known on the mechanism and significance of TTLL-mediated modification of non-tubulin substrates. Here, we found that TTLL11 generates a previously unknown type of polyglutamylation by adding glutamate residues to the carboxy-terminus of a substrate protein. TTLL11 efficiently polyglutamylates the signaling protein disheveled 3 (DVL3), thereby changing the interactome of DVL3, as well as its capacity to undergo liquid-liquid phase separation (LLPS). Both carboxyterminal polyglutamylation and the resulting reduction in LLPS capacity of DVL3 were reverted by the deglutamylating enzyme CCP6, which demonstrates the causal relationship between TTLL11-mediated polyglutamylation and LLPS. We thus discovered a novel type of posttranslational modification catalyzed by a TTLL enzyme, which significantly broadens the range of proteins that can be modified by polyglutamylation, and provide first evidence that polyglutamylation can act as a regulator of protein LLPS.