InterPro domain: IPR023885

This domain contains regions binding additional 4Fe4S clusters found in various radical SAM proteins C-terminal to the domain described by IPR007197 . Radical SAM enzymes with this domain tend to be involved in protein modification, including anaerobic sulphatase maturation proteins, a quinohemoprotein amine dehydrogenase biogenesis protein, the Pep1357-cyclizingradical SAM enzyme, and various bacteriocin biosynthesis proteins [ 1 , 2 ]. SkfB from Bacillus subtilis , which catalyzes the formation of the thioether bond required for production of the sporulation killing factor SkfA [ 3 ], also contains this domain. The motif CxxCxxxxxCxxxC is nearly invariant for members of this family, although PqqE has a variant form. This domain has been named SPASM for Subtilosin, PQQ, Anaerobic Sulphatase, and Mycofactocin.

1. Biological systems discovery in silico: radical S-adenosylmethionine protein families and their target peptides for posttranslational modification. J. Bacteriol. 193, 2745-55
2. Bioinformatic evidence for a widely distributed, ribosomally produced electron carrier precursor, its maturation proteins, and its nicotinoprotein redox partners. BMC Genomics 12, 21
3. Cannibalism by sporulating bacteria. Science 301, 510-3