The Brucella Effector Protein BspF Crotonylates TRIM38 to Inhibit NF-κB and MAPK Signaling Pathway.

The type IV secretion system (T4SS) is an important virulence factor of Brucella. T4SS secretes 16 effector proteins, which affect the intracellular transport of Brucella-containing vacuoles and regulate the host immune response, helping Brucella survive and replicate in host cells. In our previous crotonylation proteomics data of HEK-293T cell proteins triggered by BspF, we found BspF crotonylated on TRIM38, which is an important modulator in the pathways of inflammation, and the crotonylation site is K142. Therefore, it is speculated that BspF may be involved in the regulation of host inflammatory response during Brucella infection. In this study, we found that BspF-mediated TRIM38K142 crotonylation promotes the ubiquitination of tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6), leading to the degradation of TRAF6 and thereby inhibiting the transduction of Nuclear factor-kappaB (NF-κB), p38 Mitogen-activated protein kinase (MAPK), and c-Jun N-terminal kinases (JNK) MAPK signaling pathways and the secretion of pro-inflammatory factors IL-6 and IL-8, which finally helps Brucella promote intracellular survival. This study provides a new theoretical basis for the intracellular survival of host innate immunity through the T4SS, provides new insights into the pathogenic mechanism and treatment of Brucella, and provides an important reference for the study of non-histone crotonylation function.