Sunday, 8 March 2020

The invisibility cloak of a fungus

Researchers find out that a fungal pathogen uses an enzyme to hide from the human immune system.

While viruses and bacteria regularly manage to infect the human organism, fungi only very rarely succeed. The reason for this is that the human immune system can recognize them very easily because their cells are surrounded by a solid cell wall of chitin and other complex sugars. Chitin is, so to speak, the alarm signal for our immune system, to which it reacts with a whole arsenal of defensive weapons. Some fungi, however, have apparently learned to avoid this fatal recognition: They possess one or more enzymes called chitin deacetylase, which they use to alter some of the chitin building blocks. This produces a chitosan, which is invisible to the immune system.

A particularly aggressive fungus, Cryptococcus neoformans, which can easily lead to a fatal infection, particularly in immunocompromised patients, has four genes that appear to encode such enzymes. So far, however, it had only been possible to show that three of them really are chitin deacetylases. The function of the fourth protein was unknown. Researchers at the University of M√ľnster (Germany) have now examined this fourth enzyme in detail. They found that this enzyme is a chitosan deacetylase which has not been described before.

It appears that chitosan deacetylase is a crucial tool of the fungus to attack its host under the chitin radar of its immune system. The complete removal of the acetic acid molecules from the chitin acts like a kind of invisibility cloak, making the fungus invisible to the immune system.


Lea Hembach, Martin Bonin, Christian Gorzelanny, Bruno M. Moerschbacher. Unique subsite specificity and potential natural function of a chitosan deacetylase from the human pathogen Cryptococcus neoformans. Proceedings of the National Academy of Sciences, 2020; 201915798 DOI: 10.1073/pnas.1915798117

Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (

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