Swapping the ThfA Leader Peptide To Be a Follower Through core peptide engineering, we have previously shown ThfB to be a highly promiscuous graspetide synthetase, enabling the generation of multicyclic peptides, cyclized proteins, and cross-linked protein dimers in cellulo . (50,51) This success in engineering alternative ThfA precursors for ThfB-mediated cyclization inspired us to investigate whether the leader sequence could be moved to a follower.