Figure 1.

Predicted FeS ligands targeted for mutagenesis in NrfC. The top section shows the primary structure of E. coli pre-NrfC with the signal peptide underlined. The diagram also shows Cys residues predicted to be involved in formation of four [4Fe–4S] centres, and these have been denoted as belonging to FeS centres 1–4 (numbering above the residues) on the basis of strong homology to formate dehydrogenase-N, another member of this family of proteins. Residues substituted in mutants M1 and M2 are indicated by asterisks and arrows, respectively. The lower part of the figure shows a predicted three-dimensional structure for NrfC from homology modelling, using the primary sequence of NrfC and the known structure of formate dehydrogenase-N subunit β (Jormakka et al, 2002).