Recently, we isolated from bovine brain a protein, TPPP/p25 and identified as p25, a brain-specific protein that induced aberrant tubulin assemblies. The primary sequence of this protein differs from that of other proteins identified so far; however, it shows high homology with p25-like hypothetical proteins sought via BLAST. Here, we characterized the binding of TPPP/p25 to tubulin by means of surface plasmon resonance; the kinetic parameters are as follows: kon, 2.4 × 104 M-1·s -1; koff, 5.4 × 10-3 s-1; and Kd, 2.3 × 10-7 M. This protein at substoichometric concentration promotes the polymerization of tubulin into double-walled tubules and polymorphic aggregates or bundles paclitaxel-stabilized microtubules as judged by quantitative data of electron and atomic force microscopies. Injection of bovine TPPP/p25 into cleavage Drosophila embryos expressing tubulin-GFP fusion protein reveals that TPPP/p25 inhibits mitotic spindle assembly and nuclear envelope breakdown without affecting other cellular events like centrosome replication and separation, microtubule nucleation by the centrosomes, and nuclear growth. GTP counteracts TPPP/p25 both in vitro and in vivo.
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|Issue number||SUPPL. 2|
|Publication status||Published - Nov 25 2003|
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