Morin hydrate attenuates <i>Staphylococcus aureus</i> virulence by inhibiting the self-assembly of α-hemolysin

AIMS: To investigate the mechanism by which morin hydrate inhibits the haemolytic activity of α-hemolysin (Hla), a channel-forming toxin that is important for the pathogenesis of disease in experimental animals, and its therapeutic effect against Staphylococcus aureus pneumonia in a mouse model. METHODS AND RESULTS: The results from the in vitro (haemolysis, western blot and cytotoxicity assays) and in vivo (mouse model of intranasal lung infection) experiments indicated that morin hydrate, a natural compound with little anti-Staph. aureus activity, could effectively antagonize the cytolytic activity of Hla, alleviate human lung cell injury, and protect against mortality of Staph. aureus pneumonia in a mouse model of infection. Molecular dynamics simulations, free energy calculations and mutagenesis assays were further employed to determine the catalytic mechanism of inhibition, which indicated that a direct binding of morin to the 'Stem' domain of Hla (residues I107 and T109) and the concomitant change in conformation led to the inhibition of the self-assembly of the heptameric transmembrane pore, thus inhibiting the biological activity of Hla for cell lysis. CONCLUSIONS: Morin inhibited Staph. aureus virulence via inhibiting the haemolytic activity of α-hemolysin. SIGNIFICANCE AND IMPACT OF THE STUDY: These findings suggested that morin is a promising candidate for the development of anti-virulence therapeutic agents for the treatment of Staph. aureus infections.

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