Iron Sulfur cluster biogenesis under stress conditions – FeStreS

Iron-sulfur (Fe-S) clusters are inorganic cofactors, ranking among the oldest catalysts in the evolution of life and are found in all kingdoms of life as parts of a large number of proteins involved in most cellular processes, such as DNA replication, repair, gene expression, metabolism, respiration or photosynthesis. Such a versatility is afforded by Fe-S clusters as they can serve as catalysts, electron carriers or redox sensors. A drawback though, is that solvent-exposed Fe-S clusters can be very vulnerable to chemicals such as reactive oxygen species (ROS) or metals, and their alteration can compromise cell physiology. Although Fe-S cluster building and insertion into polypeptides can be achieved in vitro with simply iron and sulfur in anaerobiosis, the in vivo situation is by far much more complex and a surprisingly large number of proteins are required, forming so-called Fe-S biogenesis systems. As a matter of fact, an increasing number of cellular dysfunctioning, including pathologies in human, is found to be related to mutations in genes encoding Fe-S enzymes or systems that make Fe-S clusters. Moreover, Fe-S clusters and ROS have intimate and paradoxical connections as ROS can degrade Fe-S, which by releasing Fe2+ participates to the generation of even more ROS. Established for a long time, this paradoxical relationship was recently proposed to be at the heart of the lethal effects of antibiotics.
The objective of the FeStreS project is to study how cells manage to keep on making and using Fe-S clusters under stressful conditions that are unfavourable to Fe-S building and/or stability such as iron-limitation and oxidative stress. Remarkably, E. coli has the two best conserved Fe-S biogenesis systems, ISC and SUF. Even more remarkable, despite the fact that they synthesized the same product, Fe-S custer, they exhibit many many structural and genetic differences. E. coli appears to use the ISC system when iron is available and no ROS around, whereas it uses the SUF system under iron limitation or in the presence of ROS. The FeStreS project will aim at deciphering the complex relationships between Fe-S cluster homeostasis and stress by addressing the following questions. What are the structural and chemical bases accounting for differential robustness of ISC and SUF? What are the informational circuits allowing E. coli to switch from one system to the other back and forth, as a function of the fluctuation in resource availability? How are Fe-S clusters once built, taken from inside the machineries down to cellular apo-proteins waiting for them to get active? Does heterogeneity arise in a population facing fluctuating environments? How important is the contribution of Fe-S homeostasis to bactericidal antibiotic effects?
The FeStreS project addresses these questions by taking advantage of our long established expertise in microbiology, genetics and bio/chemistry, and is reinforced by cutting-edge technologies and approaches such as fluorescence microscopy/microfluidic and proteomics.
Note that the FeStreS project is built on conceptual and technological advances reached in a previous ANR-funded project called Biosuf . The objective of the BIOSUF project was to understand at a very fundamental level, by combining the methods of protein chemistry, microbiology and bioinformatics, the mechanistic, physiological and evolutionary features of the processes used to insert sulfur into biological molecules. This question was addressed through the study of biosyntheses of iron-sulfur (Fe-S) cluster and of sulfurated organic compounds catalyzed by “Radical-SAM (S-adenosylmethionine)” enzymes. The current one, while keeping on a clear interdisciplinary ambition, focuses on the relationships between Fe-S and stress and over all takes the problem to the in vivo, cellular, even populational level. It is absolutely clear that FeStreS is a new and original investigation of the biology of Fe-S clusters that are essential for cells to work.