FIGURE 4.

(A) Dependence of the lipid-binding constant of synaptotagmin I C2A on the percentage of PS in a binary mixture of POPC/POPS. K_L is presented as the logarithm of the dissociation constant (1/K_L). The logarithm is provided as base 10 for ease of comparison of the values to other figures. Protein concentrations were varied from 0.2–0.55 μM. (B) Binding of synaptotagmin C2A to POPC/POPS/dansylPE (65:25:10). The lipid-binding constants were calculated through application of Eq. 1 to partition functions. The global partition function Q from setting [Tb³⁺] = 0 in Eq. 3, then reverts to 1 + K_L(L). The lipid titrant was corrected for free lipid concentration as above, accounting for protein concentration, outer leaflet lipids, and membrane coverage by C2A of five lipids.