English: The following depicts the non-ribosomal peptide synthetase of the cereulide tetrapeptide. The growing and modified peptide can be seen on each Thiolation (T) domain.
1. Module 1 (CesA1) loads a-ketoisocaproic acid and reduces it into D-a-hydroxyisocaproic acid (D-HIC).
2. Module 2 (CesA2) loads L-alanine (L-Ala) and epimerizes it to D-alanine (D-Ala). It also condenses the amide bond to form D-HIC-D-Ala.
3. Module 3 (CesB1) loads a-ketoisovaleric acid and reduces it into L-a-hydroxyisovaleric acid (L-HIV).
3.5. A lone condensation domain condenses the ester bond between L-HIV and D-Ala to form D-HIC-D-Ala-L-HIV.
4. Module 4 (CesB2) loads L-valine (L-Val). It also condenses the amide bond to form D-HIC-D-Ala-L-HIV-L-Val.