Focal targeting by human β-defensin 2 disrupts localized virulence factor assembly sites in Enterococcus faecalis

Abstract

Virulence factor secretion and assembly occurs at spatially restricted foci in some Gram-positive bacteria. Given the essentiality of the general secretion pathway in bacteria and the contribution of virulence factors to disease progression, the foci that coordinate these processes are attractive antimicrobial targets. In this study, we show in Enterococcus faecalis that SecA and Sortase A, required for the attachment of virulence factors to the cell wall, localize to discrete domains near the septum or nascent septal site as the bacteria proceed through the cell cycle. We also demonstrate that cationic human β-defensins interact with E. faecalis at discrete septal foci, and this exposure disrupts sites of localized secretion and sorting. Modification of anionic lipids by multiple peptide resistance factor, a protein that confers antimicrobial peptide resistance by electrostatic repulsion, renders E. faecalis more resistant to killing by defensins and less susceptible to focal targeting by the cationic antimicrobial peptides. These data suggest a paradigm in which focal targeting by antimicrobial peptides is linked to their killing efficiency and to disruption of virulence factor assembly.focal localization | immunofluorescence | microscopy | MprF

Deciphering the tRNA-dependent lipid aminoacylation systems in bacteria: Novel components and structural advances

“…Altogether, these findings show that aa-PGs can provide positively charged lipid microdomains that protect the septum, along with important components involved in cell wall biosynthesis, from inhibition by CAMPs. 86 …”

Dual defensin strategy for targetingEnterococcus faecalis

“…Several proteins, including Esp (2), aggregation substance (3), a collagen adhesin (4), and a pilin (5), correlate with a particular disease or exacerbate the course of infection in a model system. In PNAS, Kandaswamy et al (6) describe the targeting by human β-defensin 2 (hBD2) and resulting disorganization of the cellular machinery used by E. faecalis to secrete and anchor these proteins to the cell surface.…”

“…Although they are rugged microbes with intrinsic resistance to many antimicrobials (including detergents such as bile), enterococci are ordinarily held in check by factors of the innate immune system, including phagocytic cells and antimicrobial peptides. To understand how antimicrobial peptides target enterococci, with implications for the design of new therapeutics, Kandaswamy et al (6) investigated the early interactions between human β-defensins and the E. faecalis cell. By fluorescently labeling minimally perturbed whole cells of E. faecalis, the investigators show that both the SecA translocase and the cellular sortase SrtA localize to foci near the septum of dividing cells.…”

“…Interestingly, Kandaswamy et al (6) observed that human β-defensins, at levels below those required for inhibition of growth, bind the cell wall of E. faecalis in early growth in a focal pattern at the septum, analogous to the localization of both SecA and SrtA. Moreover, this deposition pattern was even more discrete in a multiple peptide resistance factor 2 (mprF2) mutant, which is defective in an enzyme that aminoacylates and reduces the negative charge of anionic membrane lipids (6).…”

“…Moreover, this deposition pattern was even more discrete in a multiple peptide resistance factor 2 (mprF2) mutant, which is defective in an enzyme that aminoacylates and reduces the negative charge of anionic membrane lipids (6). It therefore was of interest to know whether this pattern was congruent with the focal localization of SrtA and SecA.…”