(C) DHE transfer between liposomes by purified GRAMD1b proteins. Left: Representative time course of DHE transfer from LPM to LER mediated by either wild-type GRAMD1b proteins (WT), mutant GRAMD1b R189W proteins (R189W), mutant GRAMD1b R189W/R191A proteins (RW/RA), or buffer alone as indicated. Methyl-β-cyclodextrin (MCD) at 1 mM was used to determine DHE equilibration. Transfer of DHE from LPM to LER resulted in a decrease in fluorescence resonance energy transfer (FRET) between DHE and DNS-PE in LPM. A series of liposomes with different DHE mol% were prepared to plot a calibration curve to convert FRET signals to DHE molecules transferred (see Appendix Fig S2D and Materials and Methods). Right: Values of DHE transfer rate of GRAMD1b (WT), GRAMD1b (R189W), and GRAMD1b (RW/RA), as estimated by the FRET-based lipid transfer assay [mean ± SEM, n = 6 independent experiments for WT, n = 3 independent experiments for R189W and RW/RA 