Type II Thioesterase Restores Activity of a NRPS Module Stalled with an Aminoacyl‐S‐enzyme that Cannot Be Elongated

Fidelity and efficiency. Nonribosomal peptide synthetases, which contain domains for the activation (A), thiolation (T), and condensation (C) of amino acids (AA), are high-efficiency, high-fidelity assembly lines for synthesizing peptide natural products. Errors in a single step can have serious consequences for product formation. Type II thioesterases (TEII) might play a critical role in ensuring efficiency and accuracy in these systems, essential features in any attempt to engineer NRPSs to produce novel products.