Fig. 4

GmPOPB catalyzes peptide bond hydrolysis and macrocyclization. a The sequence of events catalyzed by GmPOPB starting with the 35mer peptide substrate. Peptide bond hydrolysis yields the leader sequence (which dissociates) and the 25mer peptide. The enzyme-bound 25mer is conformationally trapped and macrocyclization cannot proceed. The 25mer must dissociate to rearrange and re-bind only then does macrocyclization occur. Apo enzyme is shown in gray, the enzyme functioning as a protease is colored green, and functioning as a macrocyclase in blue. The peptide is colored as Fig. 1b. b A 25mer substrate yields a 17 amino-acid by-product, whereas the 13mer substrate generates a 5 amino-acid by-product, a much more economically efficient reaction. Substrates are colored as Fig. 1b