Fig. 2. Schematic drawing of the structure of three PCP tetramers. Each subunit is shown in a different color. The figure was produced using MOLSCRIPT (38). a) PfPCP, b) BaPCP, c) TlPCP. Three twofolded axes are designed the P-, Q-, and R-axes. Each subunit is in contact with two other subunits, and twofolded axes (P- and Q-axes) run through these interfaces. The R-axis runs through the center of the tetramer.