A bacterial radical S-adenosyl-L-methionine (AdoMet) enzyme that contains three [4Fe-4S] clusters. The enzyme, found in some bacteria, activates a type I sulfatase enzyme (EC 3.1.6.1) by converting a conserved L-serine residue in the active site to a unique 3-oxo-L-alanine residue that is essential for the sulfatase activity. While the enzyme from Klebsiella pneumoniae is specific for L-serine, the enzyme from Clostridium perfringens can also act on L-cysteine, see EC 1.8.98.7, cysteine-type anaerobic sulfatase-maturating enzyme.