Figure 1.

(a) Top and (b) side view of the NAT model system, i.e., the native AQP1 tetramer surrounded by a native POPC PLB (gray color) and covered with water layers on top and at the bottom (cyan color in (b)). The top and bottom water layers correspond to the extracellular and cytoplasmic aqueous regions. For clarity, the water layers are removed in (a). (c) Highlight of some of the AQP amino acid residues that are most reactive with OH radicals [40]. Cys₁₉₁ is indicated with red dashed circles in (a) and (c). The chemical structures of Cys and its oxidized form Cys sulfenic acid (i.e., Cys-SOH) are given in (c), whereas the chemical structures of POPC and its oxidized form POPC-ALD are shown in (d). These lipids are used to construct the OXL model system, whereas Cys-SOH residues are used to build the OXP model system. Note that Cys₁₉₁ is selected as the oxidation target in OXP because it can easily be oxidized and stays close to the ar/R selectivity region (see Figure 2).