Zinc-induced structural changes of the disordered tppp/p25 inhibits its degradation by the proteasome

• Zinc binds to TPPP/p25 coupled with its dimerization and enhanced tubulin polymerization activity.
• The intracellular level of TPPP/p25, a microtubule associated protein, is enhanced by zinc uptake.
• Zinc-induced structural change inhibits the degradation of TPPP/p25 by the proteasome.
• This effect occurs in cells expressing TPPP/p25 ectopically or endogenously at different levels.

Tubulin Polymerization Promoting Protein/p25 (TPPP/p25), a neomorphic moonlighting protein displaying both physiological and pathological functions, plays a crucial role in the differentiation of the zinc-rich oligodendrocytes, the major constituent of myelin sheath; and it is enriched and co-localizes with α-synuclein in brain inclusions hallmarking Parkinson's disease and other synucleinopathies. In this work we showed that the binding of Zn2 + to TPPP/p25 promotes its dimerization resulting in increased tubulin polymerization promoting activity. We also demonstrated that the Zn2 + increases the intracellular TPPP/p25 level resulting in a more decorated microtubule network in CHO10 and CG-4 cells expressing TPPP/p25 ectopically and endogenously, respectively. This stabilization effect is crucial for the differentiation and aggresome formation under physiological and pathological conditions, respectively. The Zn2 +-mediated effect was similar to that produced by treatment of the cells with MG132, a proteasome inhibitor or Zn2 + plus MG132 as quantified by cellular ELISA. The enhancing effect of zinc ion on the level of TPPP/p25 was independent of the expression level of the protein produced by doxycycline induction at different levels or inhibition of the protein synthesis by cycloheximide. Thus, we suggest that the zinc as a specific divalent cation could be involved in the fine-tuning of the physiological TPPP/p25 level counteracting both the enrichment and the lack of this protein leading to distinct central nervous system diseases.