Surface plasmon resonance (SPR) experiments.

SPR binding experiments were performed on a Biacore T200 instrument (Cytiva, Biacore, Uppsala, Sweden) at 25°C as described previously (30). The running buffer was constituted by Tris buffer complemented with 0.005% (vol/vol) P20 surfactant (Cytiva). The four biotinylated synthetic peptides (IRF3, E6AP, chim-IRF3-E6AP, and chim-E6AP-IRF3) were reversibly captured on a sensor surface using the Biotin CAPture kit (Cytiva, Biacore product code 28-9202-34). Each cycle started by injecting CAPture reagent diluted five times in running buffer over all channels for 300 seconds at a 2-μL/minute flow rate. Capture levels were between 3,700 and 4,100 relative units (RU). Biotinylated peptides were immobilized by injecting a 40 nM solution at 20 μL/minute. Contact times were adjusted to reach peptide capture levels between 5 and 30 RU. In each cycle, a reference surface served as the control for nonspecific binding of the analyte and was treated as the peptide surfaces except that the peptide injection was omitted. The MBP-HPV16 E6 analyte was used at 720 nM and then injected on the four channels for 60 seconds at a flow rate of 30 μL/minute. The postinjection phase was recorded for 180 additional seconds. At the end of each cycle, the surface was regenerated by injecting a 6 M guanidine hydrochloride solution supplemented with 250 mM sodium hydroxide for 60 seconds at 5 μL/minute followed by an additional washing step with the running buffer.