Fig. 4. Multi-site binding of OmpX to SurA.

a SDS-PAGE analysis of DSBU cross-linked SurA-OmpX. Note that the species indicated with an asterisk (*) are higher order cross-linked species of mass corresponding to multiple SurA molecules bound to OmpX, consistent with multivalent binding observed previously⁴⁶. These were not analysed further here. Source data are provided as a Source Data file. b Inter-molecular cross-links detected in the SurA-OmpX complex. The location of all Lys residues are indicated with orange arrows. c Crystal structure of SurA (PDB 1M5Y²⁷). Purple spheres indicate identified cross-link sites (Supplementary Table 7). Samples contained 5 µM SurA, 5 µM OmpX, 0.24 M urea, 50 µM–2 mM DSBU, in 10 mM potassium phosphate buffer, pH 8.0, 25 °C. A representative mass spectrum for each cross-link can be found in Supplementary Data 1.