HtrA, fatty acids, and membrane protein interplay in Chlamydia trachomatis to impact stress response and trigger early cellular exit

UNLABELLED: Chlamydia trachomatis is an intracellular bacterial pathogen that undergoes a biphasic developmental cycle, consisting of intracellular reticulate bodies and extracellular infectious elementary bodies. A conserved bacterial protease, HtrA, was shown previously to be essential for Chlamydia during the reticulate body phase, using a novel inhibitor (JO146). In this study, isolates selected for the survival of JO146 treatment were found to have polymorphisms in the acyl-acyl carrier protein synthetase gene (aasC). AasC encodes the enzyme responsible for activating fatty acids from the host cell or synthesis to be incorporated into lipid bilayers. The isolates had distinct lipidomes with varied fatty acid compositions. A reduction in the lipid compositions that HtrA prefers to bind to was detected, yet HtrA and MOMP (a key outer membrane protein) were present at higher levels in the variants. Reduced progeny production and an earlier cellular exit were observed. Transcriptome analysis identified that multiple genes were downregulated in the variants especially stress and DNA processing factors. Here, we have shown that the fatty acid composition of chlamydial lipids, HtrA, and membrane proteins interplay and, when disrupted, impact chlamydial stress response that could trigger early cellular exit.IMPORTANCE: Chlamydia trachomatis is an important obligate intracellular pathogen that has a unique biphasic developmental cycle. HtrA is an essential stress or virulence protease in many bacteria, with many different functions. Previously, we demonstrated that HtrA is critical for Chlamydia using a novel inhibitor. In the present study, we characterized genetic variants of Chlamydia trachomatis with reduced susceptibility to the HtrA inhibitor. The variants were changed in membrane fatty acid composition, outer membrane proteins, and transcription of stress genes. Earlier and more synchronous cellular exit was observed. Combined, this links stress response to fatty acids, membrane proteins, and HtrA interplay with the outcome of disrupted timing of chlamydial cellular exit.</p

Structure-activity analysis of peptidic Chlamydia HtrA inhibitors

Chlamydia trachomatis high temperature requirement A (CtHtrA) is a serine protease that performs proteolytic and chaperone functions in pathogenic Chlamydiae; and is seen as a prospective drug target. This study details the strategies employed in optimizing the irreversible CtHtrA inhibitor JO146 [Boc-Val-Pro-ValP(OPh)2] for potency and selectivity. A series of adaptations both at the warhead and specificity residues P1 and P3 yielded 23 analogues, which were tested in human neutrophil elastase (HNE) and CtHtrA enzyme assays as well as Chlamydia cell culture assays. Trypsin and chymotrypsin inhibition assays were also conducted to measure off-target selectivity. Replacing the phosphonate moiety with α-ketobenzothiazole produced a reversible analogue with considerable CtHtrA inhibition and cell culture activity. Tertiary leucine at P3 (8a) yielded approximately 33-fold increase in CtHtrA inhibitory activity, with an IC50 = 0.68 ± 0.02 µM against HNE, while valine at P1 retained the best anti-chlamydial activity. This study provides a pathway for obtaining clinically relevant inhibitors