Griseusin B

Streptomyces are well-known producers of a range of different secondary metabolites, including antibiotics and other bioactive compounds. Recently, it has been demonstrated that "silent" biosynthetic gene clusters (BGCs) can be activated by heterologously expressing transcriptional regulators from other BGCs. Here, we have activated a silent BGC in Streptomyces sp. CA-256286 by overexpression of a set of SARP family transcriptional regulators. The structure of the produced compound was elucidated by NMR and found to be an N-acetyl cysteine adduct of the pyranonaphtoquinone polyketide 3'-O-α-d-forosaminyl-(+)-griseusin A. Employing a combination of multi-omics and metabolic engineering techniques, we identified the responsible BGC. These methods include genome mining, proteomics and transcriptomics analyses, in combination with CRISPR induced gene inactivations and expression of the BGC in a heterologous host strain. This work demonstrates an easy-to-implement workflow of how silent BGCs can be activated, followed by the identification and characterization of the produced compound, the responsible BGC, and hints of its biosynthetic pathway.

A divergent modular strategy for the enantioselective total synthesis of 12 naturally-occurring griseusin type pyranonaphthoquinones and 8 structurally-similar analogues is described. Key synthetic highlights include Cu-catalyzed enantioselective boration-hydroxylation and hydroxyl-directed C-H olefination to afford the central pharmacophore followed by epoxidation-cyclization and maturation via diastereoselective reduction and regioselective acetylation. Structural revision of griseusin D and absolute structural assignment of 2a,8a-epoxy-epi-4'-deacetyl griseusin B are also reported. Subsequent mechanistic studies establish, for the first time, griseusins as potent inhibitors of peroxiredoxin 1 (Prx1) and glutaredoxin 3 (Grx3). Biological evaluation, including comparative cancer cell line cytotoxicity and axolotl embryo tail inhibition studies, highlights the potential of griseusins as potent molecular probes and/or early stage leads in cancer and regenerative biology.

AbstractTo minimize competitive overlap, carnivores modify one of their critical niche axes: space, time, or resources. However, we currently lack rules for how carnivore communities operate in human-dominated landscapes. We simultaneously quantified overlap in the critical niche axes of a simple carnivore community-an apex carnivore (Puma concolor), a dominant mesocarnivore (Lycalopex culpaeus), and a subordinate small carnivore (Lycalopex griseus)-in a human landscape featuring pastoralists and semidomestic carnivores (i.e., dogs, Canis familiaris). We found that dominant species had strong negative effects on the space use of subordinate ones, which ultimately created space for subordinate small carnivores. Humans and dogs were strictly diurnal, whereas the native carnivore community was nocturnal and exhibited high temporal overlap. Dietary overlap was high among the native carnivores, but dogs were trophically decoupled, largely because of human food subsidies. Our results show that in landscapes with evident human presence, temporal and dietary partitioning among native carnivores can be limited, leaving space as the most important axis to be partitioned among carnivores. We believe that these findings-the first to simultaneously assess all three critical niche axes among competing carnivores and humans and their associated species (i.e., domesticated carnivores)-are transferable to other carnivore communities in human-modified landscapes.