FIGURE 5.

Putative mode of ligand binding. The mode of binding of ligands by SARS CoV PLpro (A) and IBV PLpro (B and C) is different. A, P1–P4 amino acids (orange sticks) of ubiquitin tethered by SARS CoV PLpro. Amino acids of PLpro within 4 Å of the ligand are shown as sticks. B and C, mode of binding of P1–P4 residues of ubiquitin (orange sticks) by IBV PLpro inferred by superimposing the ubiquitin from the structure of SARS CoV PLpro bound with ubiquitin (Protein Data Bank code 4M0W) on the structure of IBV PLpro (red schematic). Amino acids within 4 Å of the ligand are shown (magenta sticks). The location of the BL1-like loop and its proximity to the P4 residue are shown in C.