Browsing by Author "MACCIONI, RB"

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    A TAU FRAGMENT CONTAINING A REPETITIVE SEQUENCE INDUCES BUNDLING OF ACTIN-FILAMENTS
    (1993) MORAGA, DM; NUNEZ, P; GARRIDO, J; MACCIONI, RB
    Much indirect evidence suggests that the interconnections of actin microfilaments with the microtubule system are mediated by microtubule-associated proteins (MAPs). In this study we provide new data to support the interaction of a specific tubulin-binding domain on tau with actin in vitro. In actin polymerization assays, the synthetic peptide VRSKIGSTENLKHQPGGG, corresponding to the first repetitive sequence Of tau protein, increased turbidity at 320 nm in a dose-dependent fashion. A salient feature of the tau peptide-induced assembly process is the formation of a large amount of actin filament bundles, as revealed by electron microscopic analysis. An increase in the tau peptide concentration resulted in a proportional increase in the bundling of actin filaments. It is interesting that a gradual decrease of pH within the range 7.6-4.7 resulted in a higher effect Of tau peptide in promoting bundles of actin filaments. A similar pH-dependent effect was observed for tau protein-induced bundling. An analysis of the mechanisms that operate in the peptide induction of actin filament bundles suggests the involvement of electrostatic forces, because the neutralization of epsilon-aminolysyl residues by selective carbamoylation resulted in a complete loss of the peptide induction of actin bundles. The data suggest that a tau repetitive sequence (also found in MAP-2 and MAP-4) containing a common tubulin binding motif may constitute a functional domain on tau for the dynamics of the interconnections between actin filaments and microtubules.
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    CALMODULIN BINDS TO A TUBULIN BINDING-SITE OF THE MICROTUBULE-ASSOCIATED PROTEIN-TAU
    (1990) PADILLA, R; MACCIONI, RB; AVILA, J
    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.