(B) Liposome tethering by purified GRAMD1b proteins. Left: Representative time course of liposome tethering, as assessed by turbidity of mixtures containing both LPM and LER together with either wild-type GRAMD1b proteins (WT), mutant GRAMD1b R189W proteins (R189W), mutant GRAMD1b R189W/R191A proteins (RW/RA), or buffer alone as indicated. Turbidity, as assessed by measuring absorbance values at 405 nm, reflects clustering of liposomes due to tethering of LPM and LER. Right: Values of turbidity corresponding to the end of the experiment as indicated by the arrow (mean ± SEM, n = 6 independent experiments for WT, n = 3 independent experiments for buffer alone, R189W, and RW/RA; Dunnett's multiple comparisons test, **P < 0.0001) 