A new mechanism of posttranslational polyglutamylation regulates phase separation and signaling of the Wnt pathway protein Dishevelled.
Polyglutamylation is a reversible post-translational modification that is catalyzed by enzymes from the tubulin tyrosine ligase-like (TTLL) family. Here, we found that TTLL11 generates a previously unknown type of polyglutamylation initiated by the addition of a glutamate residue to the free C-terminal carboxyl group of a substrate protein. TTLL11 efficiently polyglutamylates the Wnt signaling protein Disheveled 3 (DVL3), thereby changing the interactome of DVL3, as well as it increases its capacity to get phosphorylated, to undergo liquid-liquid phase separation (LLPS), and to act in the non-canonical Wnt pathway. 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, which significantly broadens the range of proteins that can be modified by polyglutamylation and provides the first evidence that polyglutamylation can act as a regulator of protein LLPS.