Cryptococcus neoformans Stops Pumping Iron

Cryptococcus neoformans is a well know fungal pathogen that can cause severe infections of the pulmonary and nervous systems. Infections of people with well functioning immune systems are rare but in those with compromised systems such as those with HIV, this opportunistic yeast is responsible for encephalitis and fungal meningitis.

Cryptococcus neoformans

Of course it needs its daily recommended allowance of vitamins and minerals. A Study conducted by scientists from Konkuk University and Chung-Ang University in Republic of Korea seeks to specifically check out the effect iron regulation has on C. neoformans day to day life.

Influence of Iron Regulation on the Metabolome of Cryptoccocus neoformans.

You see, iron is important for a whole host of processes. It is used in the tricarboxylic acid cycle, amino acid creation, respiration, as well as making lipids and sterols. The thing is, too much iron is bad, if level get to high it leads to the creation of oxygen radicals. Oxegyn radicals are bad mamma jammas; they cause things like DNA breakage and protein denaturing. Yup, iron is important, but you need to keep it in check or all kinds of things are going wrong.

It has been established that Cir1 is an important regulatory protein for iron transport and homeostasis. The same study showed Cir1 to be important to melanin formation and synthesis of spore capsules, things very important to the virulence of C. neoformans. With all of the metabolic pathways influenced by deletion of this protein and its importance on the regulation of iron, the team of researchers chose see the metabolic effects the deletion of Cir1 would have in order to get a large picture on its function in C. neoformans.

To study this they utilized Gas chromatography mass spectrometry and chemometric multivariate statistics to analyze the metabolomic profiles of a wild type and a Cir1 mutant strain lacking the regulatory protein. They attempted to find the pathway(s) most affect by a lack of Cir1 and how it affects the metabolome of C. neoformans. The strains were grown on a range of media, with varying amounts of available iron.

Because of the similarity and complexity between the Cir1 mutant and the wild type, the researchers used principle component analysis on the 972 peaks shown in the data sets, comparing the variation in 18 discriminative metabolites that showed significant difference.

When compared between the high and low iron mediums the chosen metabolites of the Cir1 strain showed little changes despite a significantly increased level of iron present in the Cir1 mutant cells. That led the team to conclude that iron availability was only responsible for minor differences in C. neoformans.

However, when looking at the regulation of genes in the wild type things were a little different. 483 genes were down-regulated and 250 were up-regulated in low iron vs high iron growth medium. Most of those differently expressed genes had to do with iron transport and homeostasis, as well as DNA repair and metabolism.

The study also showed dramatic influence of Cir1 on metabolism and production of those molecules involved.

One of the most interesting differences in the mutant was a large increase in glucose production. An increase in glucose implies that deleting the Cir1 had affects on the major carbon assimilation processes because glucose is metabolized in glycolysis and important in the TCA cycle and respiration. The TCA cycle and respiration are also influenced by iron so there is potentially connection there.

Combining those observations allows for the suggestion that an increase in intracellular iron and glucose are evidence of lowered iron requiring processes like glycolysis and respiration.

Another increase was shown in ergostol and its derivatives. Ergostol is the major constituent in fungal cell walls and is the target of some antifungal drugs. This increase of production is evidence of why Cir1 mutants have been demonstrated to be more resistant to anti-fungal treatment. A change in the production of ergostol and its derivative molecule  means a remodeling of membrane biosynthesis.

The basis of many secondary messengers, inositol was also increased significantly in the Cir1 mutant. This suggested up-regulation of inositol metabolism in Cir1 deletion was further seen by an increase in virulence important genes that are derived from it.

All of this together revealed that deletion of one of the major iron regulating genes in C. neoformans also impacts several of the iron required pathways. Taking out the Cir1 protein led to a change in respiration, glycolysis, as well as synthesis of membranes and messenger pathways.

When studying the effects of a protein, gene, or any other molecule on a system, this study demonstrates that one must remember, life is complex as all get out. While not everything is truly intertwined, the impact one thing has another is often multifaceted and unpredictable.

Awesome Researchers:
Jung Nam Choi, Jeongmi Kim, Won Hee Jung, & Choong Hwan Lee (2012). Influence of Iron Regulation on the Metabolome of Cryptococcus neoformans PLoS One DOI: 10.1371/journal.pone.0041654

Photo cred:
Centers for Disease Control and Prevention's Public Health Image Library  identification number #3771