CALMODULIN BINDS TO A TUBULIN BINDING-SITE OF THE MICROTUBULE-ASSOCIATED PROTEIN-TAU
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1990
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Abstract
Previous studies have demonstrated that the microtubule-associated proteins MAP-2 and tau interact selectively with common binding domains on tubulin defined by the low-homology segments .alpha.(430-441) and .beta. (422-434). It has been also indicated that the synthetic peptide VRSKIGSTENLKHQPGGG corresponding to the first tau repetitive sequence represents a tubulin binding domain on tau. The present studies show that the calcium-binding protein calmodulin interacts with a tubulin binding site on tau defined by the second repetitive sequence VTSKCGSLGNIHHKPGGG. It was shown that both tubulin and calmodulin bind to tau peptide-Sepharose affinity column. Binding of calmodulin occurs in the presence of 1 mM Ca2 + and it can be eluted from the column with 4 mM EGTA. These findings provide new insights into the regulation of microtubule assembly, since Ca2 +/calmodulin inhibition of tubulin polymerization into microtubules could be mediated by the direct binding of calmodulin to tau, thus preventing the interaction of this latter protein with tubulin.