Proteomics-Driven Molecular Mechanism of Cinnamaldehyde against Methicillin-Resistant Staphylococcus aureus Infection: Covalent Modifications of Sortase A and Aconitase.

Cinnamaldehyde (CA) from Cinnamomum cassia shows strong antimicrobial activity against MRSA. This study used proteomics and high-resolution mass spectrometry with an MRSA-infected cell model to explore CA's antimicrobial mechanisms. CA covalently modifies Sortase A's active site cysteine (Cys184), a key enzyme for anchoring virulence factors to the MRSA cell wall. This modification inhibits Sortase A's activity, blocking virulence factor anchoring and impairing MRSA's adhesion, infection, and immune evasion. CA also covalently modifies Aconitase's [4Fe-4S] cluster active sites (Cys509, Cys512), disrupting citrate isomerization in the TCA cycle and causing ATP depletion. These modifications lead to NADH and glutathione depletion, increased ROS levels, oxidative stress, and bacterial death in MRSA. CA forms thiohemiketal and thioester structures with the active site cysteines of Sortase A and Aconitase. These findings provide potential targets for new anti-MRSA drugs and support CA's antibacterial application.