The potential of the diverse chemistries present in natural products (NP) for biotechnology and medicine remains untapped because NP databases are not searchable with raw data and the NP community has no way to share data other than in published papers. Although mass spectrometry techniques are well-suited to high-throughput characterization of natural products, there is a pressing need for an infrastructure to enable sharing and curation of data. We present Global Natural Products Social molecular networking (GNPS, http://gnps.ucsd.edu), an open-access knowledge base for community wide organization and sharing of raw, processed or identified tandem mass (MS/MS) spectrometry data. In GNPS crowdsourced curation of freely available community-wide reference MS libraries will underpin improved annotations. Data-driven social-networking should facilitate identification of spectra and foster collaborations. We also introduce the concept of ‘living data’ through continuous reanalysis of deposited data.

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The chemical diversity of natural products is fueled by the emergence and ongoing evolution of biosynthetic pathways in secondary metabolism [1][2][3][4][5] . However, co-evolution of enzymes as functional assemblies for metabolic diversification is not well understood, especially at the biochemical level. Here, two parallel enzyme assemblies with an extraordinarily high sequence identity form a β-branched cyclopropane in the curacin A (Cur), and a vinyl chloride group in the jamaicamide (Jam) pathways, respectively. The assemblies include a halogenase (Hal), a 3-hydroxy-3-methylglutaryl (HMG) enzyme cassette for β-branching and an enoyl reductase domain (ER). Bioinformatic analysis indicated that the corresponding genes were inserted into modular polyketide synthases (PKSs) via acyltransferase (AT) domain replacement. The Hal from CurA, and the dehydratases (ECH 1 s) and decarboxylases (ECH 2 s) within the HMG enzyme cassettes and ERs from both Cur and Jam were assessed biochemically to determine the mechanism of cyclopropane and vinyl chloride formation. Unexpectedly, the polyketide β-branching pathway was modified by introduction of a γ-chlorination step on (S)-HMG mediated by Cur Hal, a nonheme Fe II , α-ketoglutarate (α-KG)-dependent halogenase 6 . In a divergent scheme, Cur ECH 2 was found to catalyze formation of the α,β C=C enoyl thioester, whereas Jam ECH 2 formed a vinyl chloride moiety by selectively generating the corresponding β,γ C=C (enoyl thioester) of the 3-methyl-4-chloroglutaconyl decarboxylation product. A non-conserved Tyr 82 residue in Cur ECH 2