Study uncovers how tuberculosis bacteria fuel themselves during infection

Researchers at The Hospital for Sick Children (SickKids) have uncovered how the bacteria that causes tuberculosis fuels itself during infection, providing new insights into one of the world's deadliest infectious diseases. 

The study, published in The EMBO Journal, provides the first detailed 3D structure of a protein called EtfD, which the bacterium Mycobacterium tuberculosis uses to extract energy from lipids (fats), along with the first laboratory test capable of directly measuring its activity. Together, these advances are giving researchers tools to begin early-stage drug discovery focused on this essential metabolic pathway. 

"By providing both a structural model and an assay for EtfD, we now have a toolkit to begin addressing a system that slows down treatment and helps the bacterium develop resistance to antibiotics. This is the first step toward developing better and shorter treatment regimens for tuberculosis," says Dr. John Rubinstein, Senior Scientist in the Molecular Medicine program at SickKids and senior author on the paper. 

How TB bacteria turn lipids into energy 

Tuberculosis (TB), an infection that primarily affects the lungs, is the most common cause of death by infectious disease worldwide. Drug‑resistant strains are rising, partly because of the ability of TB bacteria to enter a dormant state and survive for long periods within lipid‑rich areas it creates in the lung. There, the bacteria feed on lipids from damaged cells for energy, becoming more tolerant to any antibiotics it is exposed to and harder to kill.

Long courses of medication that can last six months to a year or more, combined with difficult side effects, can make it challenging for patients to take their medication consistently. 

Using high‑resolution cryo‑electron microscopy at the Nanoscale Bomedical Imaging Facility, the research team led by Rubinstein and first author Gautier Courbon produced the first structural model of EtfD. 

The structure reveals that EtfD acts like a wire, moving energy released from broken‑down lipids into the system the bacterium uses to produce adenosine triphosphate (ATP), the molecule that powers its survival during infection. 

Toward more effective TB treatment

As part of the study, Courbon also developed the first biochemical assay that can measure EtfD activity. Although EtfD had previously been proposed as a promising target, including by co‑authors Drs. Sabine Ehrt and Dirk Schnappinger at Weill Cornell Medicine, researchers lacked a way to measure its activity. 

"The assay finally lets us see EtfD working in real time. It shows us when this wire‑like pathway is active and when it is blocked, which is essential for screening inhibitors," says Courbon, a PhD Candidate in the Rubinstein Lab. "Knowing what EtfD looks like at the atomic level also helps us pinpoint where a compound could bind and how we might improve potential drug candidates." 

Early collaborative work with the SPARC Drug Discovery Facility will soon begin to test libraries of potential compounds that could block EtfD. 

With the assay and the structure now available to research teams, this study highlights how structural biology and the Molecular Medicine program at SickKids is helping lay the foundation for identifying compounds that may one day help shorten treatment duration. 

"TB has been with humanity for thousands of years. With drug‑resistant strains on the rise, understanding and targeting its survival strategies is essential if we are going to develop the next generation of TB treatments that give clinicians the best possible tools to support their patients," adds Rubinstein.