Ribosome-independent peptide biosynthesis: the challenge of a unifying nomenclature.

The first machineries for non-ribosomal peptide (NRP) biosynthesis were uncovered over 50 years ago, and the dissection of these megasynthetases set the stage for the nomenclature system that has been used ever since. Although the number of exceptions to the canonical biosynthetic pathways has surged in the intervening years, the NRP synthetase (NRPS) classification system has remained relatively unchanged. This has led to the exclusion of many biosynthetic pathways whose biosynthetic machineries violate the classical rules for NRP assembly, and ultimately to a rupture in the field of NRP biosynthesis. In an attempt to unify the classification of NRP pathways and to facilitate the communication within the research field, we propose a revised framework for grouping ribosome-independent peptide biosynthetic pathways based on recognizable commonalities in their biosynthetic logic. Importantly, the framework can be further refined as needed.