Dryocrassin ABBA Inhibits the Function of LLO and SortaseA to Alleviate the Virulence of Listeria monocytogenes

Listeria monocytogenes is a deadly foodborne pathogen, its virulence factors Listeriolysin O (LLO) and Sortase A (SrtA) play a critical role in its infection and have been identified as key targets for developing its inhibitor. This study reveals that the natural compound Dryocrassin ABBA (ABBA) alleviates the toxicity of L. monocytogenes by effectively inhibiting the functions of LLO and SrtA. ABBA bound to the binding pocket of LLO and inhibited the formation of its oligomers, which in turn reduced the ability of LLO to lyse mammalian erythrocytes. When co-cultured with L. monocytogenes, ABBA reduced the hemolytic activity of the cultural supernatant. In addition, ABBA bound to SrtA and reduced its transpeptide activity, which in turn resulted in a reduction in the formation of bacterial biofilm, the adhesion and invasion of L. monocytogenes to cells. Thr415 and Lys505 of LLO, and Asn92 and Pro220 of SrtA are critical residues on promoting their binding with ABBA by forming non-covalent weak interactions. ABBA reduced the cytotoxicity and inflammatory responses mediated by L. monocytogenes, and demonstrated protective effect against L.monocytogenes-infected Galleria mellonella. ABBA did not show anti-L. monocytogenes properties and cytotoxicity effect under the test concentrations, promising its potential to be developed as an anti-L. monocytogenes infection agent.