PE_PGRS3 ensures provision of the vital phospholipids cardiolipin and phosphatidylinositols by promoting the interaction between M. tuberculosis and host cells

Analysis of complete genomes of Mycobacterium tuberculosis sublineage 2.1 (Proto-Beijing) revealed the presence of three pe_pgrs3-pe_pgrs4-like genes

Mycobacterium tuberculosis Complex (MTBC), the etiological agent of tuberculosis (TB), demonstrates considerable genotypic diversity with distinct geographic distributions and variable virulence profiles. The pe-ppe gene family is especially noteworthy for its extensive variability and roles in host immune response modulation and virulence enhancement. We sequenced an Mtb genotype L2.1 isolate from Chiangrai, Northern Thailand, using second and third-generation sequencing technologies. Comparative genomic analysis with two additional L2.1 isolates and two L2.2.AA3 (Asia Ancestral 3 Beijing) isolates revealed significant pe-ppe gene variations. Notably, all L2.1 isolates harbored three copies of pe_pgrs3-pe_pgrs4-like genes (pe_pgrs3*, pe_pgrs4*, and pe_pgrs4), different from L2.2.AA3 and H37Rv strains. Additionally, ppe53 was duplicated in all but H37Rv, and ppe50 was deleted in L2.1 isolates, contrasting with an extended ppe50 in an L2.2 isolate (Mtb 18b), which contains an additional SVP motif. Complete deletion of ppe66 and loss of wag22 were observed in L2.1 isolates. These findings highlight the high structural variability of the pe-ppe gene family, emphasizing its complex roles in Mtb-host immune interactions. This genetic complexity offers potentially critical insights into mycobacterial pathogenesis, with significant implications for vaccine development and diagnostics.

Unraveling the potential of graphene quantum dots against Mycobacterium tuberculosis infection

Introduction

The emergence of drug-resistant Mycobacterium tuberculosis (Mtb) strains has underscored the urgent need for novel therapeutic approaches. Carbon-based nanomaterials, such as graphene oxide (GO), have shown potential in anti-TB activities but suffer from significant toxicity issues.

Methods

This study explores the anti-TB potential of differently functionalized graphene quantum dots (GQDs) - non-functionalized, L-GQDs, aminated (NH2-GQDs), and carboxylated (COOH-GQDs) - alone and in combination with standard TB drugs (isoniazid, amikacin, and linezolid). Their effects were assessed in both axenic cultures and in vitro infection models.

Results

GQDs alone did not demonstrate direct mycobactericidal effects nor trapping activity. However, the combination of NH2-GQDs with amikacin significantly reduced CFUs in in vitro models. NH2-GQDs and COOH-GQDs also enhanced the antimicrobial activity of amikacin in infected macrophages, although L-GQDs and COOH-GQDs alone showed no significant activity.

Discussion

The results suggest that specific types of GQDs, particularly NH2-GQDs, can enhance the efficacy of existing anti-TB drugs. These nanoparticles might serve as effective adjuvants in anti-TB therapy by boosting drug performance and reducing bacterial counts in host cells, highlighting their potential as part of advanced drug delivery systems in tuberculosis treatment. Further investigations are needed to better understand their mechanisms and optimize their use in clinical settings.

Immunological effects of the PE/PPE family proteins of Mycobacterium tuberculosis and related vaccines

Tuberculosis (TB) is a chronic infectious disease caused by Mycobacterium tuberculosis (Mtb), and its incidence and mortality are increasing. The BCG vaccine was developed in the early 20th century. As the most widely administered vaccine in the world, approximately 100 million newborns are vaccinated with BCG every year, which has saved tens of millions of lives. However, due to differences in region and race, the average protective rate of BCG in preventing tuberculosis in children is still not high in some areas. Moreover, because the immune memory induced by BCG will weaken with the increase of age, it is slightly inferior in preventing adult tuberculosis, and BCG revaccination cannot reduce the incidence of tuberculosis again. Research on the mechanism of Mtb and the development of new vaccines against TB are the main strategies for preventing and treating TB. In recent years, Pro-Glu motif-containing (PE) and Pro-Pro-Glu motif-containing (PPE) family proteins have been found to have an increasingly important role in the pathogenesis and chronic protracted infection observed in TB. The development and clinical trials of vaccines based on Mtb antigens are in progress. Herein, we review the immunological effects of PE/PPE proteins and the development of common PE/PPE vaccines.

Tale of Twin Bifunctional Second Messenger (p)ppGpp Synthetases and Their Function in Mycobacteria

M. tuberculosis, an etiological agent of tuberculosis, requires a long treatment regimen due to its ability to respond to stress and persist inside the host. The second messenger (p)ppGpp-mediated stress response plays a critical role in such long-term survival, persistence, and antibiotic tolerance which may also lead to the emergence of multiple drug resistance. In mycobacteria, (pp)pGpp molecules are synthesized predominantly by two bifunctional enzymes-long RSH-Rel and short SAS-RelZ. The long RSH-Rel is a major (p)ppGpp synthetase and hydrolase. How it switches its activity from synthesis to hydrolysis remains unclear. RelMtb mutant has been reported to be defective in biofilm formation, cell wall function, and persister cell formation. The survival of such mutants has also been observed to be compromised in infection models. In M. smegmatis, short SAS-RelZ has RNase HII activity in addition to (pp)Gpp synthesis activity. The RNase HII function of RelZ has been implicated in resolving replication-transcription conflicts by degrading R-loops. However, the mechanism and regulatory aspects of such a regulation remain elusive. In this article, we have discussed (p)ppGpp metabolism and its role in managing the stress response network of mycobacteria, which is responsible for long-term survival inside the host, making it an important therapeutic target.

PGRS domain structures: Doomed to sail the mycomembrane

The impact of artificial intelligence (AI) in understanding biological processes is potentially immense. Structural elucidation of mycobacterial PE_PGRS is sustenance to unveil the role of these enigmatic proteins. We propose a PGRS “sailing” model as a smart tool to diffuse along the mycomembrane, to expose structural motifs for host interactions, and/or to ship functional protein modules at their C-terminus.

Imidazole-Thiosemicarbazide Derivatives as Potent Anti-Mycobacterium tuberculosis Compounds with Antibiofilm Activity

Mycobacterium tuberculosis (Mtb) is an intracellular pathogenic bacterium and the causative agent of tuberculosis. This disease is one of the most ancient and deadliest bacterial infections, as it poses major health, social and economic challenges at a global level, primarily in low- and middle-income countries. The lack of an effective vaccine, the long and expensive drug therapy, and the rapid spread of drug-resistant strains of Mtb have led to the re-emergence of tuberculosis as a global pandemic. Here, we assessed the in vitro activity of new imidazole-thiosemicarbazide derivatives (ITDs) against Mtb infection and their effects on mycobacterial biofilm formation. Cytotoxicity studies of the new compounds in cell lines and human monocyte-derived macrophages (MDMs) were performed. The anti-Mtb activity of ITDs was evaluated by determining minimal inhibitory concentrations of resazurin, time-kill curves, bacterial intracellular growth and the effect on biofilm formation. Mutation frequency and whole-genome sequencing of mutants that were resistant to ITDs were performed. The antimycobacterial potential of ITDs with the ability to penetrate Mtb-infected human macrophages and significantly inhibit the intracellular growth of tubercle bacilli and suppress Mtb biofilm formation was observed.

Stringent Response in Mycobacteria: From Biology to Therapeutic Potential

Mycobacterium tuberculosis is a human pathogen that can thrive inside the host immune cells for several years and cause tuberculosis. This is due to the propensity of M. tuberculosis to synthesize a sturdy cell wall, shift metabolism and growth, secrete virulence factors to manipulate host immunity, and exhibit stringent response. These attributes help M. tuberculosis to manage the host response, and successfully establish and maintain an infection even under nutrient-deprived stress conditions for years. In this review, we will discuss the importance of mycobacterial stringent response under different stress conditions. The stringent response is mediated through small signaling molecules called alarmones “(pp)pGpp”. The synthesis and degradation of these alarmones in mycobacteria are mediated by Rel protein, which is both (p)ppGpp synthetase and hydrolase. Rel is important for all central dogma processes—DNA replication, transcription, and translation—in addition to regulating virulence, drug resistance, and biofilm formation. Rel also plays an important role in the latent infection of M. tuberculosis. Here, we have discussed the literature on alarmones and Rel proteins in mycobacteria and highlight that (p)ppGpp-analogs and Rel inhibitors could be designed and used as antimycobacterial compounds against M. tuberculosis and non-tuberculous mycobacterial infections.

Proline-Glutamate/Proline-Proline-Glutamate (PE/PPE) proteins of Mycobacterium tuberculosis: The multifaceted immune-modulators

The PE/PPE proteins encoded by seven percent (7%) of Mycobacterium tuberculosis (Mtb) genome are the chief constituents to pathogen's virulence reservoir. The fact that these genes have evolved along ESX secretory system in pathogenic Mtb strains make their investigation very intriguing. There is lot of speculation about the prominent role of these proteins at host pathogen interface and in disease pathogenesis. Nevertheless, the exact function of PE/PPE proteins still remains a mystery which calls for further research targeting these proteins. This article is an effort to document all the facts known so far with regard to these unique proteins which involves their origin, evolution, transcriptional control, and most important their role as host immune-modulators. Our understanding strongly points towards the versatile nature of these PE/PPE proteins as Mtb's host immune sensors and as decisive factors in shaping the outcome of infection. Further investigation on these proteins will surely pave way for newer and effective vaccines and therapeutics to control Tuberculosis (TB).