These data demonstrate that total deletion of the SUF machinery from Proteobacteria can be complemented Talazoparib mw using the entire SUF operon from Firmicutes. It is quite remarkable that the complemented strain was able to grow on unsupplemented glycerol minimal medium. This indicates that complementation of iscS∷kan by the sufCDSUB operon of E. faecalis is also occurring. As complementation did not occur using the sufS or sufSE recipients, it is clear that there are differences between
the sufSE and sufSU complexes, perhaps with respect to their mechanisms of action and/or interaction between each other and with other SUF proteins. The present paper discusses the possibility of genetic complementation among Proteobacteria [Fe–S] cluster biosynthetic machinery and the E. faecalis sufCDSUB operon. Complementation was not observed when individual proteins from the E. faecalis SUF system were expressed in E. coli strains lacking putative homolog proteins. In contrast, complementation was verified when the E. faecalis SUF system
was inserted into the E. coli strain lacking both ISC and SUF systems. It appears that the presence of all complements of a given system enables proper functional interactions, which do not otherwise occur among proteins from different systems, even BMS-354825 mw though these proteins are predicted to have similar functions. The first aspect addressed by the authors was to check the capacity of E. faecalis sufCDSUB operon to replace functions of the ISC system from Proteobacteria. For this next purpose, A. vinelandii, the model organism from which the ISC system was first identified, was used for recombinant events. Azotobacter vinelandii are nitrogen-fixing bacteria, containing the NIF system for nitrogenase maturation (Jacobson et al., 1989a, b); however, the NIF system
is active only under nitrogen-fixing conditions. In contrast, the ISC system of A. vinelandii contains the housekeeping iscRSUA-hscBA-fdx genes for [Fe–S] cluster formation (Zheng et al., 1998). Whole sufCDSUB was not able to complement ISC operon. Several matches for specific homologous gene complementation were tried but all of them were synthetically lethal. This is in accordance with the vast diversity found between the systems analyzed. In the E. faecalis SUF operon, sufU is the only ortholog of the ISC system and, although sharing conserved cysteine residues, sufU and iscU show several structural dissimilarities, mainly in key protein–protein interaction sites (Riboldi et al., 2009). Likewise, E. faecalis do not have any ATC that could mimic iscA and/or sufA functions. In addition, the primary structure of SufB from E. faecalis is not similar to E. coli SufB, as it lacks several conserved cysteine residues responsible for the [Fe-S] cluster assembly in Proteobacteria. These differences could explain the lack of complementation observed for the Proteobacteria ISC system.