Figure 7

Substrate placement and binding pocket in the Plasmodium and human PNP enzymes. The schematic diagrams represent the human and parasite forms of the enzyme at the catalytic state. The diagram for Plasmodium parasite enzymes (left) is based on the arsenolytic-intermediate-state Pf PNP and the sulphate-bound Pv PNP structures, with the residues numbered according to the P. falciparum enzyme (+1 for Pv PNP), while that for human PNP (right) is based on the transition-state-analogue complexes (PDB ID: 1RR6, [6]) and refined atomic coordinates [20]. Amino acids lining the active sites are represented by spheres, coloured grey for non-polar, green for uncharged polar, blue for positively charged and red for negatively charged amino acids with bound water molecules shown as dark blue spheres. Note residues labelled 'a' are from the parent subunit, while those labelled 'b' from the neighbouring subunit in a dimer pair.