Members of this rare protein family are SPASM domain-containing radical SAM enzymes that closely resembly ScfB, the thioether bridge-forming peptide modification enzyme of the SCIFF (Six Cysteines in Forty-Five residues) RiPP precursor. However, they form their own, distinctive clade within is ScfB-like family, are noticeably different toward the N-terminus, and are found in genomic contexts in which no ScfA-like encoded protein can be found. The protein is designated an orphan maturase because no substrate has been identified.
Jiyao W et al.(2023). "The conserved domain database in 2023.",