| Fe-S clusters are ancient prosthetic groups. Research on Fe-S cluster biogenesis has seen vast advances in the last decades. The identification of the Nif, Isc, and Suf Fe-S cluster assembly pathways among different organisms revealed the in vivo complexity of this process. Current, unanswered questions include the in vivo source of iron, a detailed clarification of persulfide mobilization and the mechanism of Fe-S cluster assembly and transfer to cluster-dependent targets. Suf is a captivating system because the stress condition under which it is activated resembles the host defense mechanism against pathogenic bacteria. Studies on the Escherichia coli K-12 experimental model have provided the platform for elucidating Suf function. In this study we have narrowed the possibilities of starting cysteinate sulfur acceptor in the proposed scaffold protein, SufB, via the use of proteomic tools. In addition, a fortuitous observation of in vivo heme b co-purifying with the SufBCD complex led to the identification of a low-spin, six-coordinate bis-His ferric heme iron center with SufBCD and opened the possibility of a role for heme b as a putative iron source for the Suf system. |
