Non-canonical thioesterases in bacterial non-ribosomal peptide biosynthesis.

α/β hydrolase fold thioesterases (TEs) play fundamentally important roles in polyketide and non-ribosomal peptide biosynthesis. Type-I TEs, fused at the C-terminus of multi-modular enzymatic assembly lines, dictate the overall molecular shapes of assembly-line products, while standalone type-II TEs maintain assembly-line activity through proofreading functions. Beyond these established roles, recent studies have elucidated several distinct TE functions that expand the functional versatility of these enzymes. This review summarizes recently discovered non-canonical functions of TEs in bacterial non-ribosomal peptide biosynthesis.