Ca-dependent binding of actin to gelsolin

AbstractCa2+ of 0.3–1.0 μM induces both the exposure of tryptic cleavage sites within the gelsolin molecule inaccessible in the Ca-free conformation, and binding of one actin monomer to the N-terminal half of gelsolin. On the other hand, gelsolin-induced enhancement of pyrene actin fluorescence was observed only above 50 μM Ca2+, and a ternary actin/gelsolin complex preformed in 200 μM Ca2+ was stable only above 30 μM Ca2+. These results provide direct evidence for Ca-induced transitions from closed to open conformation of the gelsolin molecule in the range of 3×10-7 to 10−6 M Ca2+. They also suggest that Ca2+>10−5 M is required to stabilize actin–actin contacts in the 2:1 actin/gelsolin complex