[Show abstract][Hide abstract] ABSTRACT: Macrophage infectivity potentiators (Mips) are immunophilin proteins and essential virulence factors for a range of pathogenic organisms. We have applied a structural biology approach to characterize a Mip from Burkholderia pseudomallei (BpML1), the causative agent of melioidosis. Crystal structure and nuclear magnetic resonance analysis of BpML1 in complex with known macrocycles and other derivatives led to the identification of a key chemical scaffold. This scaffold possesses inhibitory potency for BpML1 without immunosuppressive components of related macrocycles. Biophysical characterization of a compound series with this scaffold allowed binding site specificity in solution, and potency determinations for rank-ordering the set. The best compounds in this series possess low micromolar affinity for BpML1, bind at the site of enzymatic activity, and inhibit a panel of homologous Mip proteins from other pathogenic bacteria, without demonstrating toxicity in human macrophages. Importantly, the in vitro activity of BpML1 is reduced by these compounds, leading to decreased macrophage infectivity and intracellular growth of Burkholderia pseudomallei. These compounds offer the potential for activity with a new class of antimicrobial target, and present the utility of a structure-based approach for novel antimicrobial drug discovery.
[Show abstract][Hide abstract] ABSTRACT: The macrophage infectivity potentiator (MIP) protein is a major virulence factor of Legionella pneumophila, the causative agent of Legionnaires' disease. MIP belongs to the FK506-binding proteins (FKBP) and is necessary for optimal intracellular survival and lung tissue dissemination of L. pneumophila. We aimed to identify new small-molecule inhibitors of MIP by starting from known FKBP12 ligands. Computational analysis, synthesis, and biological testing of pipecolic acid derivatives revealed a promising scaffold for new MIP inhibitors.