Leader
Escherichia coli contains two machineries involved in iron-sulfur cluster biosynthesis. The first one, referred to as ISC (Iron-Sulfur-Cluster), is essential for general biogenesis of iron-sulfur clusters in bacteria under normal growth conditions. Homologues of these proteins have also been identified in eucaryotes suggesting a highly conserved mechanism. The second machinery, SUF (SulFUr), works under iron limitation and oxidative stress. These two systems are endowed with properties allowing the correct assembly of iron and sulfur atoms to form a cluster (Figure 1). In our laboratory we aim to understand at a fundamental level, the mechanistic features of the processes used to insert iron and sulfur atoms into target-proteins. This is achieved by combining the methods of biochemistry, protein chemistry and spectroscopy.
Figure 1: Iron-sulfur clusters machineries in Escherichia coli
More recently, our researches showed a direct sulfur transfer from SufE to SufA and from SufE to SufB, through a transpersulfuration reaction, leading to the formation of persulfide (cys-S-SH) and polysulfide (cys-S-(S)n-SH) species located at the conserved cysteine residues (Figure 2). Also recently, we were able to identify a potential iron donor for the [Fe-S] cluster assembly, the bacterial frataxin homologous CyaY.
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Figure 2: Summary of knowledge on the SUF system and our objectives for future years (indicated by the « ? » symbol).
For the future, we will pursue the following objectives using different approaches mentioned in the introduction:
1- Identify the SufBCD function (role of the ATPase activity, role of the [Fe-S] cluster on SufB);
2- Structural and functional characterization of the as-isolated SufA protein containing its metallic cofactor [Fe-S]; Comparison to the in vitro results;
3- Unravel the molecular mechanism by which iron-sulfur clusters are assembled within scaffold protein, using SufA as a model. Identify whether iron or sulfide, is incorporated first at the active site and identify which transfer mechanisms to the target proteins are involved.
