Structural basis for polyglutamate chain initiation and elongation by TTLL family enzymes

Kishore K. Mahalingan, E. Keith Keenan, Madeleine Strickland, Yan Li, Yanjie Liu, Haydn L. Ball, Martin E. Tanner, Nico Tjandra, Antonina Roll-Mecak

Research output: Contribution to journalArticlepeer-review

24 Scopus citations


Glutamylation, introduced by tubulin tyrosine ligase-like (TTLL) enzymes, is the most abundant modification of brain tubulin. Essential effector proteins read the tubulin glutamylation pattern, and its misregulation causes neurodegeneration. TTLL glutamylases post-translationally add glutamates to internal glutamates in tubulin carboxy-terminal tails (branch initiation, through an isopeptide bond), and additional glutamates can extend these (elongation). TTLLs are thought to specialize in initiation or elongation, but the mechanistic basis for regioselectivity is unknown. We present cocrystal structures of murine TTLL6 bound to tetrahedral intermediate analogs that delineate key active-site residues that make this enzyme an elongase. We show that TTLL4 is exclusively an initiase and, through combined structural and phylogenetic analyses, engineer TTLL6 into a branch-initiating enzyme. TTLL glycylases add glycines post-translationally to internal glutamates, and we find that the same active-site residues discriminate between initiase and elongase glycylases. These active-site specializations of TTLL glutamylases and glycylases ultimately yield the chemical complexity of cellular microtubules.

Original languageEnglish (US)
Pages (from-to)802-813
Number of pages12
JournalNature Structural and Molecular Biology
Issue number9
StatePublished - Sep 1 2020

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology


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