Effects of Actin-Binding Proteins on the Thermal Stability of Monomeric Actin

Differential scanning calorimetry (DSC) was applied to investigate the thermal unfolding of rabbit skeletal muscle G-actin in its complexes with actin-binding proteins, cofilin, twinfilin, and profilin. The results show that the effects of these proteins on the thermal stability of G-actin depend on the nucleotide, ATP or ADP, bound in the nucleotide-binding cleft between actin subdomains 2 and 4. Interestingly, cofilin binding stabilizes both ATP–G-actin and ADP–G-actin, whereas twinfilin increases the thermal stability of the ADP–G-actin but not that of the ATP–G-actin. By contrast, profilin strongly decreases the thermal stability of the ATP–G-actin but has no appreciable effect on the ADP–G-actin. Comparison of these DSC results with literature data reveals a relationship between the effects of actin-binding proteins on the thermal unfolding of G-actin, stabilization or destabilization, and their effects on the rate of nucleotide exchange in the nucleotide-binding cleft, decrease or increase. These re...