TY - JOUR TI - Structural basis of ribosomal peptide macrocyclization in plants AU - Haywood, Joel AU - Schmidberger, Jason W AU - James, Amy M AU - Nonis, Samuel G AU - Sukhoverkov, Kirill V AU - Elias, Mikael AU - Bond, Charles S AU - Mylne, Joshua S A2 - Craik, Charles S VL - 7 PY - 2018 DA - 2018/01/31 SP - e32955 C1 - eLife 2018;7:e32955 DO - 10.7554/eLife.32955 UR - https://doi.org/10.7554/eLife.32955 AB - Constrained, cyclic peptides encoded by plant genes represent a new generation of drug leads. Evolution has repeatedly recruited the Cys-protease asparaginyl endopeptidase (AEP) to perform their head-to-tail ligation. These macrocyclization reactions use the substrates amino terminus instead of water to deacylate, so a peptide bond is formed. How solvent-exposed plant AEPs macrocyclize is poorly understood. Here we present the crystal structure of an active plant AEP from the common sunflower, Helianthus annuus. The active site contained electron density for a tetrahedral intermediate with partial occupancy that predicted a binding mode for peptide macrocyclization. By substituting catalytic residues we could alter the ratio of cyclic to acyclic products. Moreover, we showed AEPs from other species lacking cyclic peptides can perform macrocyclization under favorable pH conditions. This structural characterization of AEP presents a logical framework for engineering superior enzymes that generate macrocyclic peptide drug leads. KW - Helianthus annuus KW - peptide macrocyclization KW - transpeptidation KW - protease catalysis JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -