Heavy metal battle during tuberculosis: Kupyaphores as Mycobacterium tuberculosis’s chemical arsenal

Work done in the lab of Dr. Rajesh S. Gokhale and Dr. Siddhesh S. Kamat at National Institute of Immunology and IISER, Pune

About author

Kritee Mehdiratta is a passionate infection biologist who earned her Bachelor’s degree in Zoology from Miranda House, University of Delhi. She followed it up with more research-oriented masters in Biomedical Sciences from Dr. B. R. Ambedkar Centre for Biomedical Research, University of Delhi. She recently finished her doctoral thesis under the supervision of Dr. Rajesh S. Gokhale and Dr. Vivek T. Natarajan from CSIR-Institute of Genomics and Integrative Biology, New Delhi. She hopes to explore further the dynamics of host-pathogen interactions from a systemic perspective and make significant contributions to TB management in India.

Interview

How would you explain your research outcomes to the non-scientific community?

Upon internalization of pathogens like Mycobacterium tuberculosis (Mtb), the causative agent of the deadly disease tuberculosis (TB), infected host cells are known to modulate their intracellular chemical milieu to restrict microbial growth. Prominent among these compositional changes are the metal ions. Host cells restrict metal ion bioavailability to starve and limit pathogen’s survival as part of nutritional immunity. It thus becomes mandatory for the intracellular Mtb to acquire these essential metal ions from the host pools to ensure successful survival and establishment of infection. While Mtb iron-chelating siderophores- mycobactin, were characterized back in 1965, it is peculiar that similar low molecular weight high-affinity molecules have not been discovered for other critical biological transition elements, zinc, thus far.

A cryptic gene cluster consisting of 5 genes spanning 10.8 kbp is mapped to the Mtb genome, which over the years has been implicated in Mtb virulence, without exactly delineating the chemical identity of the metabolic end product nor its significance in TB pathophysiology. Our structural elucidation studies revealed this metabolite to be a diacyl-diisonitrile lipopeptide, which we termed ‘Kupyaphores’ (‘kupya’ – rare metals in Sanskrit and ‘phores’ – carrier in Latin).

Functional studies showed kupyaphores to play a dominant role in Mtb zinc homeostasis. Mtb cells were found to secrete kupyaphores into the environment to sequester zinc. Additionally, the kupyaphore non-producer Mtb mutant strain was unable to mobilize host free zinc efficiently upon infection and showed reduced fitness in in vivo murine TB infection studies. Our study thus unraveled a novel zinc acquisition strategy of Mtb that could modulate host-pathogen interactions and disease outcomes.

How do these findings contribute to your research area?

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), results in immense mortality with myriad pathophysiological presentations. The progressive loss of muscle mass and function, referred to as TB-cachexia, is one such neglected systemic manifestation. Interestingly, TB patients also show systemic metal dyshomeostasis that cannot be reversed by oral supplementation. Our studies identify a novel Mtb metallophore that facilitates the successful colonization of bacilli. These diacylated-diisonitrile lipopeptides, named kupyaphores, are secreted out to equip Mtb to adapt to dynamic zinc flux changes in host macrophages upon infection. In metastatic cancer, muscle wasting is attributed to the redistribution of zinc. Identification of kupyaphore-mediated zinc acquisition strategy could hence provide opportunities in the future to investigate systemic zinc dysbiosis and associated manifestations in TB patients.

What was the exciting moment during your research?

The most exciting moment for me during this research project would be the serendipitous discovery of our molecule – kupyaphores. Based on the retro-biosynthetic approach, I was given the task of theoretically predicting the chemical identity of this molecule. However, the amateur chemist that I am, I messed up the chemical mass calculations, and the experimentally obtained masses differed by one carbon unit. Motivated by my mentor, Dr. Gokhale, to embrace the mistake and learn from it, we re-analyzed all the theoretical chemical structures and aligned them with the experimentally identified molecules to finally ascertain the chemical structure of this enigmatic metabolite!

What do you hope to do next?

I have always been driven by this saying – ‘Somewhere, something incredible is waiting to be known. I hope I continue making more such exciting discoveries in my academic path ahead, which I intend to translate from bench to bedside.

Where do you seek scientific inspiration from?

I find it somewhat amusing that while pursuing complex data-driven science, I draw my scientific inspiration from these words of famous Indian mythologist Devdutt Patnaik:

“Within infinite myths lies the eternal truth
Who sees it all?
Varuna has but a thousand eyes,
Indra has a hundred,
You and I, only two.”

This quote always reminds me of the limitless possible answers that exist to my scientific question at hand and my limited abilities to answer them. It humbles and empowers me at the same time!

How do you intend to help Indian science improve?

Our scientific response during the COVID-19 pandemic, from designing innovative diagnostics to building indigenous vaccines, has brilliantly demonstrated what all the Indian scientists are capable of. I intend to enhance this workforce by performing more interdisciplinary research, and collaborating with researchers from varied fields to deliver and meet our nation’s scientific goals.

Reference

Mehdiratta K., Singh S., Sharma S., Bhosale R.S., Choudhury R., Masal D.P., Manocha A., Dhamale B.D., Khan N., Vivekanad A., et al., Kupyaphores are zinc homeostatic metallophores required for colonization of Mycobacterium tuberculosis, Proct Nat. Aca. Sc., 2022 (https://www.pnas.org/doi/abs/10.1073/pnas.2110293119)

Edited by: Manveen K Sethi

Meet the managers

Surabhi Sonam

Surabhi Sonam is an Assistant Professor. Along with teaching and research, she has a very strong interest in science communication. She has written several poems and blogs to communicate scientific principles and concepts. She is also volunteering with several science communication platforms as a content contributor and content editor. Under her supervision, her students have launched a scicomm magazine, Scinion which represents science in verbal and visual forms.

Sejal Dixit

Sejal Dixit is currently a 3rd-year student pursuing BSc triple majors in biotechnology, zoology, and chemistry from CHRIST (Deemed to be University). She loves to read, be it short stories, novels, magazines, or research articles. She is working with her college professor on a few papers, and wishes to pursue her master’s degree in stem cells and regenerative medicines. She has no problem socializing with new people and possesses leadership qualities. Her hobbies are dancing and traveling.

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