The effect of mouse twinfilin-1 on the structure and dynamics of monomeric actin

• The effect of twinfilin 1 on actin is only partially uncovered.
• Twinfilin 1 decreased the accessibility of the nucleotide binding region on actin.
• Twinfilin 1 decreased the flexibility of the small domain of actin.
• The overall thermodynamic stability of actin increased due to twinfilin 1.
• Actin can adapt its conformation to meet the demands of its partner proteins.

The effect of twinfilin-1 on the structure and dynamics of monomeric actin was investigated with fluorescence spectroscopy and differential scanning calorimetry experiments. Fluorescence anisotropy measurements proved that G-actin and twinfilin-1 could form a complex. Due to the formation of the complexes the dissociation of the nucleotide slowed down from the nucleotide-binding pocket of actin. Fluorescence quenching experiments showed that the accessibility of the actin bound ε-ATP decreased in the presence of twinfilin-1. Temperature dependent fluorescence resonance energy transfer and differential scanning calorimetry experiments revealed that the protein matrix of actin becomes more rigid and more heat resistant in the presence of twinfilin-1. The results suggest that the nucleotide binding cleft shifted into a more closed and stable conformational state of actin in the presence of twinfilin-1.