PPE57 Cooperates with MmpL3 to Mediate Bacterial Lipid Transport and Promote Persistent Infection of Mycobacterium tuberculosis.

Mycobacterium tuberculosis (M. tb) possesses a unique, lipid-rich cell envelope that is critical for virulence, drug resistance, and persistence. Here, we identify the PPE family protein PPE57 as a key regulator of mycolic acid transport and host lipid exploitation. PPE57 physically interacts with the essential lipid transporter MmpL3, promoting trehalose monomycolate (TMM) translocation, enhancing trehalose dimycolate (TDM) synthesis, and increasing cell wall lipid content. Site-directed mutagenesis identified G175 as a critical residue for PPE57-MmpL3 binding. Deletion of PPE57 reduces cell wall thickness, alters lipid composition, and impairs biofilm formation. Mechanistically, PPE57 facilitates bacterial cholesterol acquisition, and during infection, activates the host PPAR-γ pathway in macrophages, leading to enhanced cholesterol uptake, lipid droplet accumulation, and increased intracellular triglyceride and cholesteryl ester levels. These changes provide a nutrient-rich niche that promotes bacterial survival and persistence. In a mouse model of infection, PPE57 deficiency results in reduced bacterial burden, milder lung pathology, and diminished lipid droplet-positive cell accumulation in lung tissues. These findings establish PPE57 as an essential accessory component of the MmpL3 lipid transport system, bridging mycobacterial cell wall assembly with host nutrient exploitation during persistent infection.