a, Cartoon overlay of the structures of BuMiaB (blue) and TmRimO (PDB:4JC0) (grey). b, Electrostatic surface potential of TmRimO (blue is positive, red is negative, and grey is neutral). c, Amino acid sequence alignment of BuMiaB and TmRimO. The overall architecture of BuMiaB is similar to that of TmRimO, with RMSDs of 1.5 and 1.6 Å for the two independent RimO molecules over 324 and 329 Cαs, respectively (Table S1). In the RimO X-ray crystal structure, the two [Fe4S4] clusters are 7.3 Å apart (nearest ion in each cluster) and are connected by a pentasulfide bridge spanning the unique (non-cysteinyl-ligated) irons of each cluster. This same pentasulfide bridge is observed in the BuMiaB structure, wherein the clusters are 6.8 Å apart (see Extended Data Fig. 2a).