In vitro liposome aggregation and fusion induced by YqiC. (A) Time course of DPPC/DPPA SUV aggregation monitored by light scattering and (B) time course of aqueous content mixing was measured after addition of YqiC protein. Equimolar amounts of terbium (Tb)- and dipicolinic acid (DPA)-loaded SUV were premixed in 10 mM Tris-HCl (pH 8.0), 50 mM NaCl, and 1 mM EDTA. The fluorescence of the Tb(DPA)3 complex formed after the mixing of aqueous contents by protein addition was measured at 545 nm over incubation time. The measurements were taken in 50 mM Tris-HCl buffer (pH 8.0) (open circles) or 50 mM sodium acetate buffer (pH 4.0) (close circles) at 25°C. The liposomes were composed of DPPC and DPPA in a molar ratio of 75:25. The lipid:protein molar ratio was 100: 1. The data presented are the results of a representative experiment of three independent repetitions.