Zn2+-Induced Rearrangement of the Disordered TPPP/p25 Affects Its Microtubule Assembly and GTPase Activity

Tubulin polymerization promoting protein/p25 (TPPP/p25) modulates the dynamics and stability of the microtubule system and plays crucial role in the myelination of oligodendrocytes. Here we showed by CD, fluorescence, and NMR spectroscopies that Zn2+ is the first ligand that induces considerable rearrangement of the disordered TPPP/p25. Zinc finger motif (His(2)Cys(2)) (His(61)-Cys(83)) was identified within the flexible region of TPPP/p25 straddled by extended unstructured N- and C-terminal regions. The specific binding of the Zn2+ to TPPP/p25 induced the formation of molten globule but not that of a well-defined tertiary structure. The Zn2+-induced partially folded structure accommodating the zinc binding motif is localized at the single Trp(76)-containing region as demonstrated by fluorescence resonance energy transfer and quenching experiments. We showed that the Zn2+-induced change in the TPPP/p25 structure modified its interaction with tubulin and GTP coupled with functional consequences: the TPPP/p25-promoted tubulin polymerization was increased while the TPPP/p25-catalyzed GTPase activity was decreased as detected by turbidimetry and by malachite green phosphate release/P-31 NMR assays, respectively. The finding that the Zn2+ of the bivalent cations can uniquely influence physiological relavant interactions significantly contributes to our understanding of the role of Zn2+ uptake TPPP/p25 processes in the differentiation/myelination of oligodendrocytes possessing a high-affinity Zn2+ uptake mechanism.