Mechanism of action of S-100 protein(s) on brain microtubule protein assembly

The inhibitory effect of S-100 on microtubule protein assembly is inversely related to the microtubule protein concentration and/or the temperature of assembly. Moreover, the S-100-induced decrease in the rate and extent of assembly is positively correlated with the length of the lag of assembly. When microtubule fragments are added to the microtubule protein solution, the S-100 effect is reduced but not abolished. These data suggest that S-100 interferes with both the nucleation and the elongation of microtubules. Since S-100 also inhibits the assembly of purified tubulin, S-100 is suggested to affect the microtubule assembly by interacting with and sequestering tubulin.