Three computational approaches to PNP discovery. The dereplication approach [19, 20, 21, 22, 23] relies on chemical databases and/or spectral libraries of known PNPs, and it can only discover known PNPs or their variants. The identification approach [24, 25, 26] uses genome mining and peptidogenomics to links PNP genotypes to their chemotypes. Sequencing approach [22, 27, 28, 29] is the last resort for discovering novel PNPs when no genomic information is available (or genome mining efforts fail) and when chemical database does not include a PNP of interest. Spectral networks [11] are crucial for the success of all these approaches.