The mechanism of action of Na glutamate, lysine HCl, and piperazine-N,N'-bis(2-ethanesulfonic acid) in the stabilization of tubulin and microtubule formation

Preferential interaction measurements between proteins and monosodium glutamate were carried out to arrive at an understanding of the mechanism of its strong effect on tubulin stability and self-assembly into microtubules. For all proteins studied, i.e. bovine serum albumin, lysozyme, beta-lactoglobulin, and calf brain tubulin, the protein showed a large preferential hydration in the presence of monosodium glutamate. The enhancement of tubulin self-association by monosodium glutamate can be interpreted in terms of the large unfavorable free energy of interaction between the additive and the protein. Preferential interactions were also examined for lysine hydrochloride, which also gave a preferential hydration of the proteins, except for tubulin. The dependence of the preferential hydration parameter on proteins was different for the two additives, suggesting the importance of net electrostatic charges of proteins in their interaction with glutamate anions and lysinium cations. The zero preferential interaction of lysine hydrochloride with tubulin indicates an affinity of the lysine cation for the protein. Both additives increased the transition temperature of proteins. This can be understood in terms of the unfavorable free energy of interaction between the additive and the protein surface, which should be even more unfavorable when the denaturation causes an increase in the surface area.