A Chlamydia trachomatis strain with a chemically generated amino acid substitution (P370L) in the cthtrA gene shows reduced elementary body production

The ClpX and ClpP2 Orthologs of Chlamydia trachomatis Perform Discrete and Essential Functions in Organism Growth and Development

Chlamydia trachomatis is the leading cause of infectious blindness globally and the most reported bacterial sexually transmitted infection both domestically and internationally. Given the economic burden, the lack of an approved vaccine, and the use of broad-spectrum antibiotics for treatment of infections, an understanding of chlamydial growth and development is critical for the advancement of novel targeted antibiotics. The Clp proteins comprise an important and conserved protease system in bacteria. Our work highlights the importance of the chlamydial Clp proteins to this clinically important bacterium. Additionally, our study implicates the Clp system playing an integral role in chlamydial developmental cycle progression, which may help establish models of how Chlamydia spp. and other bacteria progress through their respective developmental cycles. Our work also contributes to a growing body of Clp-specific research that underscores the importance and versatility of this system throughout bacterial evolution and further validates Clp proteins as drug targets.

Chlamydia trachomatis is an obligate intracellular bacterium that undergoes a complex developmental cycle in which the bacterium differentiates between two functionally and morphologically distinct forms, the elementary body (EB) and reticulate body (RB), each of which expresses its own specialized repertoire of proteins. Both primary (EB to RB) and secondary (RB to EB) differentiations require protein turnover, and we hypothesize that proteases are critical for mediating differentiation. The Clp protease system is well conserved in bacteria and important for protein turnover. Minimally, the system relies on a serine protease subunit, ClpP, and an AAA+ ATPase, such as ClpX, that recognizes and unfolds substrates for ClpP degradation. In Chlamydia, ClpX is encoded within an operon 3′ to clpP2. We present evidence that the chlamydial ClpX and ClpP2 orthologs are essential to organism viability and development. We demonstrate here that chlamydial ClpX is a functional ATPase and forms the expected homohexamer in vitro. Overexpression of a ClpX mutant lacking ATPase activity had a limited impact on DNA replication or secondary differentiation but, nonetheless, reduced EB viability with observable defects in EB morphology noted. Conversely, overexpression of a catalytically inactive ClpP2 mutant significantly impacted developmental cycle progression by reducing the overall number of organisms. Blocking clpP2X transcription using CRISPR interference led to a decrease in bacterial growth, and this effect was complemented in trans by a plasmid copy of clpP2. Taken together, our data indicate that ClpX and the associated ClpP2 serve distinct functions in chlamydial developmental cycle progression and differentiation.

Nafamostat mesylate inhibits chlamydial intracellular growth in cell culture and reduces chlamydial infection in the mouse genital tract

Urogenital Chlamydia trachomatis (C. trachomatis) infection is one of the most common bacterial sexually transmitted diseases worldwide. Untreated C. trachomatis infections that ascend to the upper genital tract lead to a series of severe complications. To search for novel antichlamydial drugs, we evaluated the effect of nafamostat mesylate (NM), a synthetic serine protease inhibitor, on chlamydial infection. NM inhibited chlamydial intracellular growth and reduced both the inclusion size and number in cell culture. NM may mainly target the intracellular reticulate bodies for inhibition. NM was also effective in enhancing chlamydial clearance from mouse genital tract when NM was applied to mice via intravaginal inoculation. The vaginal NM did not significantly alter inflammatory cytokine responses in the mouse genital tract. Thus, we have demonstrated a novel role of NM in inhibiting the obligate intracellular bacterium Chlamydia.

Chlamydial-Secreted Protease Chlamydia High Temperature Requirement Protein A (cHtrA) Degrades Human Cathelicidin LL-37 and Suppresses Its Anti-Chlamydial Activity

Background

Chlamydia trachomatis is an obligate intracellular pathogen that can cause severe reproductive tract complications while ascending infection occurs. When spreading from cell to cell in a host, C. trachomatis utilizes various survival strategies to offset host defense mechanisms. One such strategy is to degrade host antimicrobial defense proteins before they can attack the invading C. trachomatis cells.

Material/Methods

We expressed and purified recombinant chlamydia high temperature requirement protein A (cHtrA) including 2 cHtrA mutants (MT-H143A and MT-S247A), and also extracted endogenous cHtrA. Proteins were identified and their purity evaluated by SDS-PAGE and Western blot. The anti-chlamydial activity and degradation of 5 antimicrobial peptides (cathelicidin LL-37, α-defensin-1 and -3, and β-defensin-2 and -4) by cHtrA and 2 cHtrA mutants (MT-H143A and MT-S247A) were tested by immunoassay and Western blot.

Results

Of the 5 antimicrobial peptides (cathelicidin LL-37, α-defensin-1 and -3, and β-defensin-2 and -4) tested, cathelicidin LL-37 showed the strongest anti-chlamydial activity. Interestingly, cHtrA effectively and specifically degraded LL-37, suppressing its anti-chlamydial activity. The 2 cHtrA mutants (MT-H143A and MT-S247A) were unable to degrade LL-37. Comparison of cHtrA activity from C. trachomatis D, L2, and MoPn strains on LL-37 showed similar responses.

Conclusions

cHtrA may contribute to C. trachomatis pathogenicity by clearing the passage of invasion by specific LL-37 degradation.

A novel protease inhibitor causes inclusion vacuole reduction and disrupts the intracellular growth of Chlamydia trachomatis

Chlamydia (C.) trachomatis, characterized by a unique biphasic life cycle, is an obligate intracellular bacterial pathogen which is responsible for the highest number of sexually transmitted bacterial infections globally. However, its pathogenic mechanisms have not been fully elucidated because of its unique developmental cycle and obligate intracellular nature. High temperature requirement (HtrA), a critical protease and chaperone, has been previously demonstrated to be essential for several functions and the replicative phase in the C. trachomatis developmental cycle. In the current study, we designed and synthesized a novel peptidomimetic inhibitor targeting C. trachomatis HtrA (CtHtrA) using homology modeling and chemical synthesis. The inhibitor was tested in chlamydia in the mid-replicative phase and resulted in a significant loss of viable infectious progeny and diminishing inclusion size and number at a relatively low concentration. This finding not only indicates that CtHtrA plays a critical role during the replicative phase of the chlamydial developmental cycle but also reveals a useful target for the design of novel anti-chlamydial agents.

Extracellular HtrA serine proteases: An emerging new strategy in bacterial pathogenesis

The HtrA family of chaperones and serine proteases is important for regulating stress responses and controlling protein quality in the periplasm of bacteria. HtrA is also associated with infectious diseases since inactivation of htrA genes results in significantly reduced virulence properties by various bacterial pathogens. These virulence features of HtrA can be attributed to reduced fitness of the bacteria, higher susceptibility to environmental stress and/or diminished secretion of virulence factors. In some Gram-negative and Gram-positive pathogens, HtrA itself can be exposed to the extracellular environment promoting bacterial colonisation and invasion of host tissues. Most of our knowledge on the function of exported HtrAs stems from research on Helicobacter pylori, Campylobacter jejuni, Borrelia burgdorferi, Bacillus anthracis, and Chlamydia species. Here, we discuss recent progress showing that extracellular HtrAs are able to cleave cell-to-cell junction factors including E-cadherin, occludin, and claudin-8, as well as extracellular matrix proteins such as fibronectin, aggrecan, and proteoglycans, disrupting the epithelial barrier and producing substantial host cell damage. We propose that the export of HtrAs is a newly discovered strategy, also applied by additional bacterial pathogens. Consequently, exported HtrA proteases represent highly attractive targets for antibacterial treatment by inhibiting their proteolytic activity or application in vaccine development.

Molecular Genetic Analysis of Chlamydia Species

Species of Chlamydia are the etiologic agent of endemic blinding trachoma, the leading cause of bacterial sexually transmitted diseases, significant respiratory pathogens, and a zoonotic threat. Their dependence on an intracellular growth niche and their peculiar developmental cycle are major challenges to elucidating their biology and virulence traits. The last decade has seen tremendous advances in our ability to perform a molecular genetic analysis of Chlamydia species. Major achievements include the generation of large collections of mutant strains, now available for forward- and reverse-genetic applications, and the introduction of a system for plasmid-based transformation enabling complementation of mutations; expression of foreign, modified, or reporter genes; and even targeted gene disruptions. This review summarizes the current status of the molecular genetic toolbox for Chlamydia species and highlights new insights into their biology and new challenges in the nascent field of Chlamydia genetics.

CtHtrA: the lynchpin of the chlamydial surface and a promising therapeutic target

Chlamydia trachomatis is the most prevalent sexually transmitted bacterial infection worldwide and the leading cause of preventable blindness. Reports have emerged of treatment failure, suggesting a need to develop new antibiotics to battle Chlamydia infection. One possible candidate for a new treatment is the protease inhibitor JO146, which is an effective anti-Chlamydia agent that targets the CtHtrA protein. CtHtrA is a lynchpin on the chlamydial cell surface due to its essential and multifunctional roles in the bacteria's stress response, replicative phase of development, virulence and outer-membrane protein assembly. This review summarizes the current understanding of CtHtrA function and presents a mechanistic model that highlights CtHtrA as an effective target for anti-Chlamydia drug development.