Figure 2.

The diffusion coefficient depends on protein size. a) Enlargement of biotinylated VSG by binding of monovalent streptavidin (mSAV) affects the diffusion coefficient (□), but does not influence the mobile fraction (▲). VSG was incorporated into supported membranes and FRAP measurements were conducted before and after mSAV was added at t₀. Depending on the concentration of mSAV (10, 5 and 2 nM), the diffusion coefficients were reduced with different kinetics. Fitting the data to a curve with variable slope (full line) yielded the half-life values (t^1/2) for the reduction of the diffusion coefficients. The dotted line marks the time of removal of unbound mSAV by washing. Data are mean values ± SD. b) Size reduction of VSG by trypsin cleavage yields a larger diffusion coefficient (□) without impacting on the mobile fraction (▲). After addition of trypsin at t₀ the diffusion coefficient doubles within 2 min. The dotted line marks the removal of trypsin by washing. Data were fitted to a curve with variable slope (full line) and are mean values ± SD.