The interdisciplinary team, spanning researchers from the University of Surrey, Imperial College London, IISc, and others, discovered Virulence Associated Dikinase (VadK), which evolved from pyruvate phosphate dikinase to histidine kinase. It regulates the methylcitrate cycle used by Mycobacterium tuberculosis to process energy sources from host lipids. Without ΔvadK mutants, the TB bacteria failed to grow in the lungs or spleen of the mouse models, showing VadK is one of the most important requirements for TB disease progression.
Even after decades of research and existing treatments, tuberculosis (TB) remains one of the leading causes of death worldwide. It has been estimated that about 25% of the world’s population carries latent TB infection.
Although that was not the case, TB was once considered ‘easily treatable’ after the discovery of streptomycin for tuberculosis. For a long time, it looked like TB could be eliminated. But the bacteria quickly developed drug resistance, especially when streptomycin was used alone as a monotherapy. By the 1950s, doctors had to combine multiple antibiotics like isoniazid and rifampicin to prevent resistance.
However, Mycobacterium Tuberculosis (Mtb), the bacteria responsible for TB, mutates quickly under antibiotic pressure, requiring months of therapy. The paper published in Cell Genomics by Prof. Tania Dottorini talks about how among the 32 overlapping indicators used in the forecast are related to TB, and their model predicts that mortality from extensively drug-resistant TB will continue to rise through 2050.
The current anti-drug treatments are still long, toxic, and less effective against resistant strains. There is an urgent need for shorter, safer therapies that can overcome resistance.
How Does Virulence Associated DiKinase (VadK) Play a Role in Methylcitrate Cycle
Every bacterium undergoes a central carbon metabolism pathway to generate energy and build essential molecules, and hence targeting CCM can cripple a bacterium’s survival machinery.
Methylcitrate cycle (MCC) is a similar metabolic pathway used by Mtb to detoxify and metabolize propionyl-CoA to pyruvate, which is a carbon source the bacterium encounters inside the host cell.
Pyruvate phosphate dikinase (PPDK) is a non-canonical histidine kinase annotated as rv1127c. It has evolved to Virulence Associated Dikinase (VadK), sitting right beside the genes encoding MCC.
VadK interacts with a set of enzymes of the MCC, and helps the bacteria to survive and replicate inside the host cell, and uses the host-derived carbon sources in regulation, as too much flux will lead to toxic buildup, while too little starves the bacteria.
This property of VadK can be effectively used as a drug target, as without VadK, TB bacteria lose their ability to regulate CCM and oxidation/reduction homeostasis and exhibit impaired bioenergetics.
But what makes VadK special is that the Anaprolectic (ANA) node in bacteria includes Pyruvate carboxylase (PCA), Phosphoenolpyruvate carboxykinase (PCK), Malic enzyme (MEZ), and pyruvate phosphate dikinase (PPDK). Humans have versions of PCA, PCK, and MEZ, but PPDK is absent in vertebrates, making PPDK an attractive drug target that won’t cause any harm to human cells.
Some Important Key Findings and Methodologies
Necessity of VadK for TB infection:
When experimented on BALB/c and C3HeB/FeJ (Kramnik) mice, which develop human-like granulomas (closer to human pathology), researchers found that the ΔvadK mutant caused much less pathology with a granuloma score of only 15.3 compared to 68.3 in wild type.
While the complemented strain (ΔvadK:vadK) restored bacterial burden in lungs and spleen of the mice, along with pathology, it is concluded that the severe attenuation of ΔvadK was directly due to the loss of VadK.
Enzymatic activity of VadK:
The structure of VadK contains an N-terminal ATP-binding domain and a central histidine kinase domain, but it lacks the C-terminal pyruvate domain canonical to PPDK, suggesting it could still act as a kinase.
This was found when researchers tested whether VadK could autophosphorylate with and without ATP and Mg²⁺ using Liquid Chromatography-Mass Spectrometry (LC-MS).
Results came out as expected; the unphosphorylated VadK variant had a mass to charge ratio of about 50k, while phosphorylated VadK showed a mass increase of 80 Da, when both ATP and Mg²⁺ were present, confirming VadK can function as a histidine kinase regulator playing an important role in the MCC cycle in TB virulence.
To Summarise Everything
VadK, a repurposed pyruvate phosphate dikinase (PPDK) in Mycobacterium tuberculosis, has evolved into a histidine kinase regulator. It is essential for the bacteria’s MCC cycle, allowing stability during growth on host-derived carbon sources like cholesterol, propionate, glycerol, etc. Without VadK, Mtb collapses metabolically and loses virulence.
Article Source: Reference Paper | Reference Article
Disclaimer:
The research discussed in this article was conducted and published by the authors of the referenced paper. CBIRT has no involvement in the research itself. This article is intended solely to raise awareness about recent developments and does not claim authorship or endorsement of the research.
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Saniya is a graduating Chemistry student at Amity University Mumbai with a strong interest in computational chemistry, cheminformatics, and AI/ML applications in healthcare. She aspires to pursue a career as a researcher, computational chemist, or AI/ML engineer. Through her writing, she aims to make complex scientific concepts accessible to a broad audience and support informed decision-making in healthcare.
