Practice question

PylB methylornithine synthase is radical S-adenosylmethionine family enzyme initiating pyrrolysine synthesis by transforming L-lysine into (3R)-3-methyl-D-ornithine. Reaction involves reductive cleavage of SAM generating 5'-deoxyadenosyl radical that abstracts hydrogen from lysine, followed by carbon skeleton rearrangement, amino group migration, epimerization. PylB harbors oxygen-sensitive [4Fe-4S] cluster essential for radical generation and conserved CxxxCxxC motif coordinating cluster. This methylornithine synthase activity expands known radical SAM superfamily functions in amino acid mutase reactions, resembling lysine 2,3-aminomutase chemistry adapted to generate branched ornithine intermediate critical for pyrroline formation providing insight into evolution of cofactor-independent radical catalysis.