Rheological measurements of the influence of 1,2-propanediol on actin/alpha-actinin gel structure: the effects of temperature and protein concentrations.

In previous studies, we demonstrated that 1,2-propanediol induces shortening and bundling of actin filaments, both in vitro and in vivo, and that it enhances actin/alpha-actinin interaction, especially at low temperature. 1,2-Propanediol also promotes homogeneous microporous networks which can be vitrified by rapid cooling. In the present study, dynamical rheological measurements were performed under various sets of experimental conditions including temperature (4 or 20 degrees C), protein concentrations (actin and alpha-actinin), and 1,2-propanediol presence or absence. Gelation kinetics were monitored, and the resulting actin mechanical properties investigated, in order to untangle the respective effects of the experimental parameters. Whether in the presence or absence of solvent, low temperature brings about a rigidification of the sample, as does high protein concentration, as expected. However, 1,2-propanediol itself involves either softening of the sample (at high temperature and low protein concentration or at low temperature and high protein concentration) or rigidification in the case of low temperature and low protein concentration. These effects result from the competition between actin/alpha-actinin affinity (enhanced by both low temperature and 1,2-propanediol), bundling of filaments (fostered by alpha-actinin for alpha-actinin/actin ratios used), rate of actin polymerization (higher at high temperature), shortening effect of 1,2-propanediol on actin filaments, and chain mobility (lower at high protein concentration). As discussed, only the combination of low temperature and low protein concentration induces full crosslinking of the system into a viscoelastic solid under the influence of 1,2-propanediol.