Bacillus anthracis Peptidoglycan Integrity Is Disrupted by the Chemokine CXCL10 through the FtsE/X Complex

Abstract

The antimicrobial activity of the chemokine CXCL10 against vegetative cells of Bacillus anthracis occurs via both bacterial FtsE/X-dependent and-independent pathways. Previous studies established that the FtsE/X-dependent pathway was mediated through interaction of the N-terminal region(s) of CXCL10 with a functional FtsE/X complex, while the FtsE/X-independent pathway was mediated through the C-terminal α-helix of CXCL10. Both pathways result in cell lysis and death of B. anthracis. In other bacterial species, it has been shown that FtsE/X is involved in cellular elongation though activation of complex-associated peptidoglycan hydrolases. Thus, we hypothesized that the CXCL10-mediated killing of vegetative cells of B. anthracis through the FtsE/X-dependent pathway resulted from the disruption of peptidoglycan processing. Immunofluorescence microscopy studies using fluorescent peptidoglycan probes revealed that incubation of B. anthracis Sterne (parent) strain with CXCL10 or a C-terminal truncated CXCL10 (CTTC) affected peptidoglycan processing and/or incorporation of precursors into the cell wall. B. anthracis ΔftsX or ftsE(K123A/D481N) mutant strains, which lacked a functional FtsE/X complex, exhibited little to no evidence of disruption in peptidoglycan processing by either CXCL10 or CTTC. Additional studies demonstrated that the B. anthracis parent strain exhibited a statistically significant increase in peptidoglycan release in the presence of either CXCL10 or CTTC. While B. anthracis ΔftsX strain showed increased peptidoglycan release in the presence of CXCL10, no increase was observed with CTTC, suggesting that the FtsE/X-independent pathway was responsible for the activity observed with CXCL10. These results indicate that FtsE/X-dependent killing of vegetative cells of B. anthracis results from a loss of cell wall integrity due to disruption of peptidoglycan processing and suggest that FtsE/X may be an important antimicrobial target to study in the search for alternative microbial therapeutics.

Structure of the Large Extracellular Loop of FtsX and Its Interaction with the Essential Peptidoglycan Hydrolase PcsB in Streptococcus pneumoniae

“…From Mycobacterium tuberculosis to Caulobacter crescentus, the ATP-binding cassette (ABC) transporter-like protein complex FtsEX acts as a key regulator of PG hydrolysis and divisome assembly (16–19). The proposed mechanism of FtsEX activation of PG hydrolases is as follows.…”

MnmE, a Central tRNA-Modifying GTPase, Is Essential for the Growth, Pathogenicity, and Arginine Metabolism of Streptococcus suis Serotype 2

“…The FtsEX protein complex plays a major role in the regulation of PG hydrolases in response to signals from cell division (Sham et al, 2013). Any disruption, either through inhibition or overactivation of the hydrolases, results in the inability to maintain the function of the cell wall (Margulieux et al, 2017), therefore, up-regulation of FtsE may impair cell growth.…”

Mechanistic insights and therapeutic opportunities of antimicrobial chemokines

“…As discussed in Section 3.1, CXCL10 localizes to the surface of B. anthracis vegetative bacilli via interaction with FtsX [55]. Recently, it was reported that this targeted interaction disrupts FtsE/X-dependent regulation of peptidoglycan hydrolase activity, resulting in uncompensated cell wall break down and bacterial cell death [82]. Analogous bactericidal effects were observed for a CXCL10-derived peptide lacking the amphipathic C-terminal α-helix [82].…”

“…Recently, it was reported that this targeted interaction disrupts FtsE/X-dependent regulation of peptidoglycan hydrolase activity, resulting in uncompensated cell wall break down and bacterial cell death [82]. Analogous bactericidal effects were observed for a CXCL10-derived peptide lacking the amphipathic C-terminal α-helix [82]. Although the C-terminus is dispensable for FtsE/X-based killing of B. anthracis , this region of CXCL10 directly mediates membrane depolarization [36].…”

“…In contrast, transposon mutant library screens of B. anthracis and E. coli have each yielded bacterial isolates less sensitive to CXCL10-mediated antimicrobial activity [55,57]; most prominently AftsX B. anthracis . While resistant mutants have informed the elucidation of unique mechanistic insights into chemokine-mediated bactericidal effects, these organisms typically display morphological and/or growth defects that indicate CXCL10 resistance is associated with a considerable fitness cost [55,57,82]. Moreover, increased chemokine concentrations effectively overcome CXCL10-resistant phenotypes [36,55].…”