FIGURE 7.

Proposed binding modes of potential substrates. A, SM (dark gray sticks) was manually placed in the substrate binding site using bound PC as a guide. A GPI anchor (stylized gray lines) is attached to the putative C-terminal ω-site. The surface of the plasma membrane is represented by a gray plane. B, comparison of potential substrate positioning in SMPDL3B and ASMase for SM and in SMPDL3B and SMPDL3A for nucleotide triphosphates. Zinc ions (gray spheres) and the nucleophilic water molecule (black sphere) are shown.