Zinc-metallochaperones of Aspergillus fumigatus are involved in ROS production and folate biosynthesis during zinc deficiency

TL;DR

This study explores how Aspergillus fumigatus uses zinc-metallochaperones to survive in zinc-deficient environments in the lungs and how these proteins contribute to fungal pathogenesis and potential antifungal drug targets.

Contribution

The first study to investigate the role of zinc-metallochaperones in a fungal pathogen and their potential as antifungal drug targets.

Findings

MchA may supply zinc to proteins involved in tetrahydrofolate (THF) biosynthesis.

MchB is essential for reactive oxygen species (ROS) production during zinc deficiency.

MchC likely supplies zinc to GTP cyclohydrolase I, a key enzyme in THF biosynthesis.

Abstract

The filamentous fungus Aspergillus fumigatus is equipped with an efficient zinc uptake system that allows this fungus to survive and grow within the very zinc-limiting environment provided by the lungs of immunosuppressed patients. To deal with zinc scarcity, A. fumigatus deploys a homeostatic and adaptive response that enables it to scavenge for and uptake zinc from host tissues. Finally, zinc ions are distributed intracellularly and lodged in fungal proteins that require them for normal functioning. It is believed that most zinc-requiring proteins acquire zinc ions to become properly metalated by competition with cellular zinc proteins. However, certain zinc proteins may exhibit inherent thermodynamic and/or physicochemical properties that hamper them from competing for zinc with other proteins during zinc deficiency, such that they can only be properly metalated if aided by specific metallochaperones. In this study, we report a comprehensive approach to the role of the zinc metallochaperones of A. fumigatus (MchA, MchB, and MchC) on both fungal physiology during zinc deficiency and fungal pathogenesis. Our data suggest that MchA might play a role in supplying zinc to one or more proteins operating in a biosynthetic pathway that use tetrahydrofolate (THF) as a cofactor; MchB is required for reactive oxygen species (ROS) production as an adaptive response to zinc deficiency, whereas MchC plays a role in THF biosynthesis, most likely by supplying zinc to GTP cyclohydrolase I. This is the first study that provides insights into the role of zinc-metallochaperones in a fungal pathogen and how they could be exploited as antifungal targets.

Aspergillus fumigatus is able to suppress nutritional immunity and obtain zinc from the lungs of immunosuppressed patients, allowing it to grow and cause invasive pulmonary aspergillosis. To combat this lethal infection, there is an urgent need for new antifungals. In this regard, tetrahydrofolate (THF) biosynthesis is a promising target. However, antifungal drugs against this process have not been developed yet, likely because only a few antifolates used as antibacterials are also active against a limited number of fungal pathogens. Our research may provide the explanation of the sensitivity to antifolates of those pathogens (Pneumocystis jirovecii, Paracoccidioides brasiliensis, and Histoplasma capsulatum), being that all lack MchC-like proteins. Moreover, we foresee that inhibition of THF biosynthesis in MchC-bearing fungal pathogens could be enhanced by inhibiting MchC activity. Also, our findings suggest the notion that ROS overproduction typically occurring in all cells during zinc deficiency may rely on proper metalation of certain zinc-dependent proteins.

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