The HtrA chaperone monitors sortase-assembled pilus biogenesis in Enterococcus faecalis
Defective pilus processing due to lack of Sortase A and HtrA elicits morphology defects in Enterococcus faecalis. In the absence of the housekeeping Sortase A enzyme, pili remain anchored to the membrane. If Sortase A and the bifunctional chaperone/protease HtrA (High Temperature Requirement A) are inactivated, membrane-bound pili accumulate and elicit aberrant morphology defects. These defects are traced back to CroRS, a two-component system that mediates antibiotic resistance in E. faecalis. This image depicts fluorescent-vancomycin staining (left) and TEM imaging (right) of wildtype E. faecalis OG1RF (top) and of E. faecalis ∆srtA∆htrA (bottom). The typical E. faecalis diplococcus shape, with a single cell septum in the middle, can be observed in the wildtype via TEM and via Van-FL staining of the cell wall (false colour gray). In stark contrast, the bottom panels highlight the aberrant morphology, defective septum placement, and septa number of a strain lacking Sortase A (srtA) and HtrA (htrA). DAPI (false colour cyan) was used to visualize DNA. ©AdelineMHYONG/NTU
Summary
Sortase-assembled pili contribute to virulence in many Gram-positive bacteria. In Enterococcus faecalis, the endocarditis and biofilm-associated pilus (Ebp) is polymerized on the membrane by sortase C (SrtC) and attached to the cell wall by sortase A (SrtA). In the absence of SrtA, polymerized pili remain anchored to the membrane (i.e. off-pathway). Here the authors show that the high temperature requirement A (HtrA) bifunctional chaperone/protease of E. faecalis is a quality control system that clears aberrant off-pathway pili from the cell membrane. In the absence of HtrA and SrtA, accumulation of membrane-bound pili leads to cell envelope stress and partially induces the regulon of the ceftriaxone resistance-associated CroRS two-component system, which in turn causes hyper-piliation and cell morphology alterations. Inactivation of croR in the OG1RF ΔsrtAΔhtrA background partially restores the observed defects of the ΔsrtAΔhtrA strain, supporting a role for CroRS in the response to membrane perturbations. Moreover, absence of SrtA and HtrA decreases basal resistance of E. faecalis against cephalosporins and daptomycin. The link between HtrA, pilus biogenesis and the CroRS two-component system provides new insights into the E. faecalis response to endogenous membrane perturbations.
Full article: https://doi.org/10.1371/journal.pgen.1011071
Why is it important?
GCIR researchers have discovered a new function of a protein called HtrA in the bacterium Enterococcus faecalis, which is often linked to infections. This bacterium uses a kind of glue called pili to stick to surfaces, which is essential for it to cause disease. Normally, these pili are properly assembled and attached to the outer shell of the bacteria by special enzymes called sortases. But sometimes, this process goes wrong, causing the pili to attach in the wrong place and stress the bacterial membrane. The HtrA protein steps in to fix this problem by helping the bacteria to deal with the misplaced pili. Without HtrA, bacteria become stressed, change shape and are more vulnerable to certain antibiotics. This discovery could lead to new ways of treating infections by acting on the bacteria's ability to handle stress and preventing them from sticking to surfaces.
2 Sept 2024