Tamarixetin Attenuated the Virulence of by Directly Targeting Caseinolytic Protease P.

, especially drug-resistant infections, is a worldwide healthcare challenge. There is a growing focus on antivirulence therapy against . Caseinolytic protease p (ClpP) is a protein hydrolase essential for pathogenicity in . A flavonoid compound, tamarixetin, which was screened in this work, was specifically able to inhibit the hydrolytic activity of ClpP on the fluorescent substrate Suc-LY-AMC with an IC of 49.73 μM, without affecting the growth of methicillin-resistant strain USA300 and was without obvious cytotoxicity. Further assays found that tamarixetin inhibited the transcription of , , , , , and genes as well as suppressed the protein expression levels of Hla and PVL. Moreover, tamarixetin was observed to dramatically inhibit the hemolytic activity of in . Consistent with that of USA300-Δ, tamarixetin was shown to increase urease expression. The thermal shift and cellular thermal shift assays showed that tamarixetin markedly changed the thermal stability of ClpP. The dissociation constant () value of tamarixetin with ClpP was 2.52 × 10 M measured by surface plasmon resonance. The molecular docking and ClpP point mutation results also demonstrated that tamarixetin had a strong interaction with ClpP. study showed that tamarixetin was effective in protecting mice from pneumonia by increasing survival, reducing lung tissue load, and slowing down the infiltration of inflammatory factors. In addition, tamarixetin was able to enhance the antibacterial activity of cefotaxime in combination. In conclusion, tamarixetin was promising as a ClpP inhibitor for infections.