Figure 5.

CLK docking site. Three contrastingly conserved residues involved in substrate recognition and docking in human Clk2 [PDB:3NR9] and the P. falciparum CLK, PfLAMMER [PDB:3LLT]. (A) Global view of the docking site, illustrating the position of the substrate RS domain and phosphorylation site. The contrastingly conserved resides are shown in cyan. (B) Human Clk2. A trio of constrastingly conserved residues (cyan), along with a nearby phenylalanine (gray), form a network of hydrogen bonds. The conserved histidine (H346) is positioned to interact with the substrate P-2 position. (C) In PfLAMMER, the three residues (cyan) are conserved as different types. A glutamine (Q739) replaces the histidine in human Clk2 seen to interact with the substrate P-2 position. The hydrogen bonding network is different: A leucine (L772) replaces the threonine seen in Clk2; an arginine (R775), corresponding to a glutamate in Clk2, is directed away from the other two conserved residues; and the glutamine (Q739) instead forms a hydrogen bond with a nearby threonine.