Figure 5.

Unusual Cys-sulfenate geometry. A. Packing interactions of the Cys-sulfenate are shown for structure FF₃, highlighting interactions with the Cys-Sγ (gray dashes and distances in Å), with the sulfenate oxygen (black dashes and distances), and a possibly unfavorable interaction between Thr45-OH and the C_P-SO⁻ (red dash and distance). 2F_O-F_C electron density evidence for the sulfenate position is also shown (blue contoured at 1.0 ρ_rms). B. Interaction of the C_P-thiolate with Pro41 (upper image) compared with that of the C_P-sulfenate (at 0.5 occupancy and labeled with its unusual bond angle and distance reported; lower image). A brown arrow shows the shift of Pro41-Cγ accommodating the sulfenate formation by relieving a steric clash (red double-headed arrow) to increase the Pro41-Cγ to sulfenate oxygen distance to 3.6 Å. C. Structure of C48S XcPrxQ including bound water and phosphate (pink model) is compared with the XcPrxQ thiolate (FF₀) and XcPrxQ sulfenate (FF₃) forms (similar models both with white carbons; FF₀ waters are gray spheres) and peroxide bound ApTpx (PDB code 3a2v, green carbons). Shift of the Pro is noted with a brown arrow. Notable observations are the C48S water and phosphate being near the FF₃ Cys-sulfenate oxygen and the ApTpx peroxide, respectively. D. Gas phase quantum mechanical calculations (Zhao and Truhlar, 2008) of methyl SO⁻, SH₂O⁺, and SH₂O⁻ species showing their energies as a function of their C-S-O bond angle (upper panel) as well as the optimized geometries and energies for the structures constrained to have a C-S-O angle of 155º. 3D figures were generated using CYLview (Legault, 2009). See Figures S4 and S5 for supporting details.