Extended Data Fig. 5: Cluster coordination in Fsr.

The top panel shows the monomeric arrangement of MtFsr (in cartoon) coloured by domains. The siroheme (purple), FAD (yellow) and the [4Fe-4S]-clusters are represented in balls and sticks. Nitrogen, oxygen, sulfur, and iron atoms are coloured respectively, in blue, red, yellow and orange. In the bottom panel, cysteines and the glutamate involved in direct [4Fe-4S]-cluster binding are highlighted, as well as the different domains of Fsr. Sequence alignment was done by Clustal Omega⁵⁸, secondary structure prediction was performed with ESPript 3.0⁵⁹. Cluster 6 is electronically connected to the siroheme. The black stars (*) indicate residues near the siroheme, proposed to bind SO₃²⁻.