Fig. 4.

Catalytic center of the active site of SARS-CoV PLpro. Unliganded X-ray crystal structure of SARS-CoV PLpro (PDB: 2FE8). The catalytic triad residues, Cys112, His273 and Asp287 are shown along with the oxyanion hole-stabilizing residue Trp107 (right panel). The flexible BL2 loop that interacts with the substrates is indicated as are the zinc ion (purple sphere) and α-helix α4 in the thumb domain. Distances between atoms are given in units of Ångströms (Å) and are indicated by dashed lines.