Investigating all possible mutations in a fungal protein reveals a new mechanism of drug resistance

What is it about?

The study of uncultivable microorganisms has always been a challenge. One such microorganism is Pneumocystis jirovecii, a human-specific fungal pathogen that causes pneumonia and is insensitive to classical antifungal drugs. Here, by using baker's yeast to express P. jirovecii's main drug target, its DHFR, an enzyme that catalyzes an essential reaction for cell growth, we were able to investigate how resistance occurs in this pathogen. By using a large-scale mutational assay, we identified virtually all single mutations that confer this protein resistance to the drug methotrexate. Overall, our results are a comprehensive portrait of this drug target's mechanisms of resistance.

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Photo by CDC on Unsplash

Photo by CDC on Unsplash

Why is it important?

In recent years, there have been more and more cases of P. jirovecii infections, and many of these have become resistant to treatment. Because of our inability to grow this pathogen in the lab, we have so far been unable to investigate its mechanisms of resistance in a comprehensive manner. Here, we have identified virtually all possible single mutations that can confer resistance to the drug methotrexate. While many of these mutations have also been reported in other eukaryotes, we find new mutations at positions of the protein not previously known to confer resistance or to be in contact with this drug, and that mutations at this position cause resistance through a mechanism called allostery.

Perspectives