Biosynthesis of a Fully Functional Cyclotide inside Living Bacterial Cells

Perfect circle. We report the biosynthesis of a natively folded cyclotide, MCoTI-II, in E. coli by intracellular backbone cyclization of a linear cyclotide–intein fusion precursor. The cyclized peptide then spontaneously folds into its native conformation. Biosynthetic access to correctly folded cyclotides allows the possibility of generating cell-based combinatorial libraries that can be screened, inside living cells, for their ability to modulate or inhibit cellular processes.