SmsB-SmsC machinery in Thermococcus kodakarensis functions as an archaeal scaffold mediating Fe-S cluster assembly

The SUF system is one of the multiprotein machineries responsible for iron-sulfur (Fe-S) cluster biogenesis. In bacterial and eukaryotic SUF systems, SufB, SufC, and SufD form a SufBC 2 D complex as the scaffold for Fe-S cluster assembly. SMS (SUF-like minimal system), composed only of SufB and SufC homologs (SmsB and SmsC) without a SufD component, has recently been established, and representatives from methanogenic archaea have been experimentally verified to function in Fe-S cluster biogenesis. SMS has been proposed to be an ancestor of the SUF system. The hyperthermophilic archaeon Thermococcus kodakarensis harbors candidate proteins for SmsB and SmsC ( Tk -SmsB and Tk -SmsC) encoded by TK0730 and TK0731 genes, respectively. As Tk -SmsB is phylogenetically positioned in a clade distinct from the previously characterized SmsB proteins from methanogens, here, we examined whether Tk -SmsB and Tk -SmsC can also function in Fe-S cluster generation and transfer. Tk -SmsB and Tk -SmsC formed a heterotetrameric SmsB 2 C 2 complex. Tk -SmsC displayed ATPase activity, and its catalytic efficiency ( k cat / K m ) increased up to 10-fold upon complex formation with Tk -SmsB. The Tk -SmsB 2 C 2 complex could generate Fe-S clusters in the presence of ferric and sulfide ions. The holo- Tk -SmsB 2 C 2 complex could transfer the Fe-S clusters to the apo-form of the Fe-S cluster-dependent lipoyl synthase LipS from T. kodakarensis , resulting in a LipS with sulfur insertion activity for lipoyl group biosynthesis. In the presence of cysteine desulfurase and ATP, the apo- Tk -SmsB 2 C 2 complex could also generate Fe-S clusters utilizing cysteine as a sulfur donor and activate LipS. IMPORTANCE A representative of an SmsB protein from T. kodakarensis ( Tk -SmsB) that lies in a clade phylogenetically distinct from those of previously verified SmsB proteins has been examined. The results demonstrate that Tk -SmsB, along with Tk -SmsC, functions as a scaffold for Fe-S cluster synthesis in T. kodakarensis , adding further support to the proposition that SMS represents the primitive form of the SUF systems widely present in bacteria and eukaryotes.