VapA of Rhodococcus equi binds phosphatidic acid

Area of Science:

• Microbiology
• Immunology
• Bacterial Pathogenesis

Background:

• Rhodococcus equi is a bacterial pathogen causing pneumonia in foals and immunocompromised individuals.
• The surface-bound virulence-associated protein A (VapA) is the primary virulence factor of R. equi.
• VapA inhibits phagosome maturation and promotes intracellular bacterial survival, but its mechanism of action is unclear.

Purpose of the Study:

• To elucidate the mechanism of action of VapA during intracellular infection.
• To investigate the interaction of VapA with host cells and its role in bacterial persistence.

Main Methods:

• Utilized soluble recombinant VapA (rVapA32-189) to rescue vapA deletion mutant replication defects.
• Observed VapA localization on bacterial surfaces and host-derived vacuoles during macrophage infection.
• Tested the in vitro interaction of rVapA32-189 with liposomes containing phosphatidic acid.

Main Results:

• Soluble rVapA32-189 rescued the intramacrophage replication defect of R. equi lacking VapA.
• rVapA32-189 enhanced the persistence of nonpathogenic Escherichia coli in macrophages.
• VapA was found on the bacterial surface and vacuole membrane during infection, and rVapA32-189 specifically bound to liposomes containing phosphatidic acid.

Conclusions:

• VapA possesses lipid-binding properties, specifically interacting with phosphatidic acid.
• This lipid-binding ability is a potential mechanism for VapA's function in promoting intracellular bacterial survival and virulence.
• The findings provide a molecular basis for VapA's role in R. equi pathogenesis.