Researchers at Albert Einstein College of Medicine of Yeshiva University have now identified a new biochemical pathway in Mtb and two novel ways to kill the bacterium. The pathway involves four enzymatic steps in the conversion of the disaccharide, trehalose, to α-glucan mediated by TreS, Pep2, GlgE (which has been identified as a maltosyltransferase that uses maltose 1-phosphate) and GlgB. Focusing on GlgE, the researchers found that blocking the enzyme induced toxic accumulation of maltose-1-phosphate, killing the bacteria in vitro and in a mouse model of infection. Inhibition of another enzyme in the pathway was non-lethal until combined with inactivation of Rv3032, a glucosyltransferase involved in a distinct α-glucan pathway. Inhibition of Rv3032 alone was also non-lethal to the bacteria.
The research validates inhibition of GlgE as therapy for TB but also highlights the potential for targeting two α-glucan pathways – a strategy that potentially leads to reduced incidence of resistance. Both approaches are also distinct from the mechanisms of currently used antibiotics.
The study is published in Nature Chemical Biology.
Oxathiazol-2-ones, such as GLR5 and HT1171, were shown to selectively and irreversibly inhibit the proteasome of MTB, whilst having little effect on the human proteasome and showing no apparent toxicity to mammalian cells. The compounds were further shown to act as suicide-substrates which cyclocarbonylate the active site threonine of the bacterial proteasome. X-ray crystallographic studies revealed major conformational changes that protect the inhibitor-enzyme intermediate from hydrolysis, allowing formation of an oxazolidin-2-one and preventing regeneration of active protease. Some of the many amino acid residues involved in the conformational changes are remote from the active site pocket and are different from those in the human proteasome, which may account for the selectivity of oxathiazol-2-ones for the bacterial system.
The World Health Organisation estimates that one third of the world’s population is latently infected with Mycobacterium tuberculosis (MTB), and that ten per cent of infected individuals will develop active disease. Current treatments for tuberculosis are effective only during active infection, and the emergence of drug-resistant strains of MTB is compromising the efficacy of existing drugs. Nicotinamide adenine dinucleotide (NAD+) synthetase is an attractive target for control of MTB since the enzyme is essential for survival of both active and latent mycobacteria, but drug discovery efforts against this enzyme have so far been hampered by a lack of structural information.
Tuberculosis is a major global cause of death and disease, with around one third of the world’s population believed to be infected with the M. Tuberculosis bacterium. Tuberculosis is known to have infected mankind since ancient times, and a 
Bone samples from a woman and child, with skeletal changes consistent with a diagnosis of tuberculosis, were examined for evidence of M. Tuberculosis infection. Rigorous precautions were taken to prevent contamination, and independent centres were used to confirm the authenticity of findings. Analysis of DNA and bacterial cell wall lipid biomarkers confirmed that both woman and child had been infected with the modern strain of M. Tuberculosis, with evidence suggesting that the child had been infected shortly after birth. The fact that the 9000-year old samples closely resemble today’s prevalent strains suggests that tuberculosis has infected humans far longer than previously thought.