Structure-function studies of polyglutamylase TTLL-11

J. Nedvedova1, M. Vosahlikova1, L. Motlova1, M. Basta1, I. Gutsche2, A. Desfosses2, C. Barinka1

1Laboratory of Structural Biology, Institute of Biotechnology of the Czech Academy of Sciences, Prumyslova 595, 252 50 Vestec, Czech Republic

2Microscopy Imaging of Complex Assemblies Group, Institute of Structural Biology, Grenoble, France

cyril.barinka@ibt.cas.cz

Microtubules (MTs) undergo various post-translational modifications, including polyglutamylation, which is the primary modification at unstructured C-terminal tubulin tails catalyzed by members of the tubulin tyrosine ligase-like (TTLL) protein family. In this report, we present the structural and functional characterization of TTLL11, the least studied member of the TTLL family. The cryoEM structure of the TTLL11/MT complex reveals a unique bipartite pattern of microtubule recognition, where the microtubule-binding and catalytic TTLL11 domains engage adjacent MT protofilaments. Biochemical experiments revealed a previously unknown glutamylation pattern, in which the polyglutamate tail directly extends the main chains of either α- or β-tubulin subunits. Finally, we have identified an intricate interplay between the enzymatic activities of TTLL11, TTL, and glutamate carboxypeptidases that governs selective modifications at individual tubulin protomers. Our work uncovers a novel type of tubulin polyglutamylation that expands the repertoire of known modifications comprising the 'tubulin code'. This code plays a major role in differentiating microtubules for distinct functions within cells and tissues.