This three-domain protein is restricted to the spirochetes and widely distributed (excepting Borrelia). It has a conserved C-terminal SPASM domain, a 4Fe-4S binding domain shared by a number of peptide-modifying and heme-modifying radical SAM proteins. It has a central radical SAM domain, although half the members have lost the signature 4Fe-4S-binding Cys residues, fail to register with the radical SAM domain definition of pfam04055, and must be considered pseudo-SAM proteins. PSI-BLAST shows a relationship between the N-terminal domain and various predicted glycosyltransferases (e.g. Bacillus subtilis SpsF) and cytidyltransferases. In some Treponema species, this protein appears to split into two tandem genes.
Jiyao W et al.(2023). "The conserved domain database in 2023.",