Fig. 2.

Domain organization and structural motifs of SARS-CoV PLpro. (A) Locations of the Ubl (pink), thumb (green), palm (yellow), and fingers (pale blue) domains are indicated by colored boxes. α-Helices (orange) and β-sheets (blue) are numbered and depicted as ribbons. The zinc atom (red) is shown in space-fill representation, and zinc-coordinating cysteines and catalytic-triad residues are shown as ball-and-stick representations. (B) Structural superposition of residues 1–71 of ubiquitin (yellow) with residues 4–62 of the Ubl domain of SARS-CoV PLpro (violet). α1 and β1–3 of PLpro are labeled. The N and C termini of the aligned proteins are indicated. The rms deviation of 50 aligned residues is 2.12 Å at 16% sequence identity. (C) Stereoview of the electron density of the tetrahedrally coordinated zinc atom. A 2F_o − F_c map is contoured at 1.8σ (blue), and an F_o − F_c omit map of the zinc atom is contoured at 8σ (red).