Figure 4.

Atomic resolution snapshots of XcPrxQ catalysis. A–D. Structures FF₀, FF₃, FF₅ and FF₈, respectively, are shown with their 2F_O-F_C electron density (blue contoured at 1.0 ρ_rms) and difference electron density between the structure of interest and FF₀ (green and red contoured at ±3.0 ρ_rms). In panels B–D, key shifts in active site residues are indicated by brown arrows with the conserved Pro flipping between two positions (noted as P1 and P2) and the Arg transitioning among three positions (R1, R2, R3). E. C_P is shown with occupancies of its oxygen adducts indicated by color (from light to dark red). 2F_O-F_C density is shown (blue contoured at 1.0 ρ_rms and for the sulfenate oxygen in FF₁ olive contoured at 0.3 ρ_rms). Density near the top of the image in structures FF₄–FF₇ is from a partially-occupied Arg conformation that occurs as the protein converts from the sulfenate to sulfinate state. F. A single image showing the 2F_O-F_C electron density peaks for C_P oxygens from all structures as single planes (solid colors at 1.0 ρ_rms, red outline 0.3 ρ_rms). The overlay shows the progression of the oxidation of C_P: from 10% SO⁻ (red outline; FF₁), 45% SO⁻ (orange; FF₂), 50% SO⁻ (yellow; FF₃), 10% SO₂⁻ (light green; FF₄), 20% SO₂⁻ (cyan; FF₅), 20% SO₂⁻ (blue; FF₆), 35% SO₂⁻ (dark blue; FF₇), 100% SO₂⁻, (purple; FF₈). All structural images were prepared using Pymol. See also Figure S3 and Figure S4.