Fig. 5. Proposed mechanism of DRAQ5^™-mediated inhibition of LtxA internalization.

In the absence of DRAQ5^™, LtxA binds to the plasma membrane, specifically cholesterol and LFA-1 (1). This causes the formation of large-scale clusters containing LtxA, LFA-1, and cholesterol (2). LtxA is then endocytosed and localized to lysosomes (3). LtxA disrupts the lysosomal membrane (H_II phase induction), to be released to the cytosol (4). In the presence of DRAQ5^™, the membrane structure is altered, which prevents LtxA from binding to the membrane lipids, but does not affect the toxin’s affinity for LFA-1. This inhibition of toxin binding prevents the necessary interactions of LtxA with the membrane that promote endocytosis