It is has been previously suggested that the protein Op18/stathmin may inte
ract with tubulin via the alpha-tubulin subunit [Larsson, N., Marklund, U.,
Melander Gradin, H., Brattsand, G. & Gullberg, M. (1997) Mel. Cell. Biol.
17, 5530-5539]. In this study we have used limited proteolysis and cross-li
nking analysis to localize further the stathmin-binding site on a-tubulin.
Our results indicate that such a binding site is in a region close to the C
-terminus of the molecule comprising residues 307 to the subtilisin-cleavag
e site on the ol-tubulin subunit. Based on a recent model of the structure
of tubulin [Nogales, E., Wolf, S.G. & Dowing, D.H. (1998) Nature (London) 3
91, 199-203], we found that this region contained the same areas that may b
e involved in longitudinal contacts of alpha-tubulin subunits within the mi
crotubule. We also observed that the binding of stathmin to tubulin can mod
ulate the binding of GTP to tubulin, as a consequence of a conformational c
hange in the beta-tubulin subunit that occurs upon interaction of stathmin
with tubulin.