Dimerization of profilin II upon binding the (GP5)3 peptide from VASP overcomes the inhibition of actin nucleation by profilin II and thymosin beta4.

Profilin II dimers bind the (GP5)3 peptide derived from VASP with an affinity of approximately 0.5 microM. The resulting profilin II-peptide complex overcomes the combined capacity of thymosin beta4 and profilin II to inhibit actin nucleation and restores the extent of filament formation. We do not observe such an effect when barbed filament ends are capped. Neither can profilin I, in the presence of the peptide, promote actin polymerization during its early phase consistent with a lower affinity. Since a Pro17 peptide-profilin II complex only partially restores actin polymerization, the glycine residues in the VASP peptide appear important.