Fig. 2. A comparison of the phosphoinositide-binding pockets of the p47phox and p40phox PX domains. The Cα atoms of the two domains were superimposed. The p47phox-PX is shown as a grey ribbon, while for p40phox the main chain ribbon (cyan) is shown only in the region of the phosphoinositide-binding pocket where the structures differ greatly. The side chains of residues that are critical for phosphoinositide binding are shown, with residue numbers for p40phox in parentheses. The side chain of Pro78 that protrudes into the binding pocket in p47phox is also illustrated. The bound PtdIns3P from the p40phox-PX structure is also shown (coloured yellow, red and cyan for carbon, oxygen and phosphorus, respectively). The sulfate in the phosphoinositide-binding pocket of p47phox-PX (grey bonds and magenta atoms) coincides with the location of the 3-phosphate of PtdIns3P. Arg42 that is associated with a CGD mutation points away from the binding site and has a role in stabilizing p47phox (Heyworth and Cross, 2002).
Fig. 5. Sequence alignment of several PX domains. The secondary structure elements and residue numbers of p47phox are shown above its sequence. The p47phox residues shown by mutagenesis to be involved in membrane binding and the p40phox residues that interact with the bound PtdIns3P are underlined. The basic residues in the second anion-binding pocket of p47phox are marked with asterisks. The regions containing the strongly conserved (R/K)-(R/K)-(Y/F) and PXXP motifs are boxed with thin lines. The portions of p40phox, p47phox and Vam7p that structurally superimpose the best are enclosed in boxes with thick lines. The sequences of PLD1 and PLD2 suggest that their PX domains, like p47phox, may have a second anion-binding pocket.
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