Fig. 5: NOS/SONOS crosslinking observed upon co-crystallization with sulfonated calpeptin in the orthorhombic space group.

Oxidative NOS and SONOS bridges are seen at four sites in the A two dimeric protomers that form both the asymmetric and biological unit (all panels, purple: oxidized NOS/SONOS structure in P2₁2₁2₁, PDB ID: 7Z3U, published in citation 21; yellow: reduced reference in P2₁2₁2₁ PDB ID: 7Z2K). B Protomer A exhibits a SONOS linkage between C22, K61, and C44 that distorts the structure from the reduced form. In contrast, C protomer B shows only a NOS linkage between C22 and K61 at this site, with the overall structure differing little from the reduced reference. D The electron density on protomer A between K102 and C156 is ambiguous, consistent with but not conclusively showing a NOS linkage at partial occupancy. In contrast, E the density at the same site on protomer B clearly shows a NOS bond at partial occupancy. F None of the residues participating in these linkages are strongly conserved besides C44. Densities shown as blue volumes are the 2mF_o-DF_c map at 1 RMSD. The same 2mF_o-DF_c map at 0.5 RMSD is overlaid as a light mesh for the K102-C156 NOS figures, to show partial occupancies more clearly.