A Prevalent Group of Actinobacterial Radical SAM/SPASM Maturases Involved in Triceptide Biosynthesis

Triceptides are ribosomally synthesized and post-translationally
modified peptides characterized by three-residue cyclophanes. The
cyclophanes are installed by radical SAM/SPASM maturases referred
to as 3-residue cyclophane forming enzymes (3-CyFEs) which catalyze
C(sp2)–Cβ(sp3) bond formation on three residue motifs at the C-terminus
of precursor peptides. Here, we bioinformatically map uncharacterized
rSAM/SPASM enzymes, referred to as Actinobacterial multiple cyclophane
maturases. The enzyme FwwB from Actinospira robinae was selected for in vivo functional studies in Escherichia coli, and was found to catalyze formation
of multiple Phe- and Trp-derived 3-residue cyclophanes. FwwB was shown
to accept a series of engineered substrates but showed specificity
for the native 3-residue motif.