Keynote: De novo sequencing of novel peptide antibiotics by tandem mass spectrometry

Proliferation of drug-resistant bacteria raises the challenge of searching for new, more efficient antibiotics. Most natural antibiotics represent cyclic nonribosomal peptides (NRPs) with nonstandard amino acids that are notoriously difficult to sequence. Moreover, the dominant technique for sequencing antibiotics (NMR) requires large amounts (milligrams) of highly purified materials that, for most compounds, are nearly impossible to obtain. Therefore, there is a need for NRPs sequencing by tandem mass spectrometry from picograms of material. Since nearly all NRPs are produced as related analogs by the same microorganism, we develop a mass spectrometry approach for sequencing all related peptides at once (in difference from the existing approach that analyzes individual peptides). We illustrate this approach by sequencing new variants of antibiotics from Bacillus brevis as well as sequencing a previously unknown family of NRPs (named Reginamides) isolated from a marine bacterial strain that produces natural products with anti-asthma activities.