Diversity, Biosynthesis and Bioactivity of Aeruginosins, a Family of Cyanobacteria-Derived Nonribosomal Linear Tetrapeptides

Prephenate decarboxylase: An unexplored branchpoint to unusual natural products

Prephenate decarboxylases are a small family of enzymes which initiate a specialized divergence from the shikimate pathway, where prephenate (2) is decarboxylated without aromatization. In addition to effecting a challenging chemical transformation, prephenate decarboxylases have been implicated in the production of rare specialized metabolites, sometimes directly constructing bioactive warheads. Many of the biosynthetic steps to natural products derived from prephenate decarboxylases remain elusive. Here, we review prephenate decarboxylase research thus far and highlight natural products that may be derived from biosynthetic pathways involving prephenate decarboxylases. We also highlight commonly encountered challenges in the structure elucidation of these natural products. Prephenate decarboxylases are a gateway into understudied biosynthetic pathways which present a high potential for the discovery of novel and bioactive natural products, as well as new biosynthetic enzymes.

My 50-Plus Years of Academic Research Collaborations with Industry. A Retrospective

A retrospective is presented highlighting the synthesis of selected "first-in-kind" natural products, their synthetic analogues, structure elucidations, and rationally designed bioactive synthetic compounds that were accomplished because of collaborations with past and present pharmaceutical and agrochemical companies. Medicinal chemistry projects involving structure-based design exploiting cocrystal structures of small molecules with biologically relevant enzymes, receptors, and bacterial ribosomes with synthetic small molecules leading to marketed products, clinical candidates, and novel drug prototypes were realized in collaboration. Personal reflections, historical insights, behind the scenes stories from various long-term projects are shared in this retrospective article.

High Structural Diversity of Aeruginosins in Bloom-Forming Cyanobacteria of the Genus Planktothrix as a Consequence of Multiple Recombination Events

Many compounds produced by cyanobacteria act as serine protease inhibitors, such as the tetrapeptides aeruginosins (Aer), which are found widely distributed. The structural diversity of Aer is intriguingly high. However, the genetic basis of this remains elusive. In this study, we explored the genetic basis of Aer synthesis among the filamentous cyanobacteria Planktothrix spp. In total, 124 strains, isolated from diverse freshwater waterbodies, have been compared regarding variability within Aer biosynthesis genes and the consequences for structural diversity. The high structural variability could be explained by various recombination processes affecting Aer synthesis, above all, the acquisition of accessory enzymes involved in post synthesis modification of the Aer peptide (e.g., halogenases, glycosyltransferases, sulfotransferases) as well as a large-range recombination of Aer biosynthesis genes, probably transferred from the bloom-forming cyanobacterium Microcystis. The Aer structural composition differed between evolutionary Planktothrix lineages, adapted to either shallow or deep waterbodies of the temperate climatic zone. Thus, for the first time among bloom-forming cyanobacteria, chemical diversification of a peptide family related to eco-evolutionary diversification has been described. It is concluded that various Aer peptides resulting from the recombination event act in chemical defense, possibly as a replacement for microcystins.

First report on adverse effects of cyanobacterial anabaenopeptins, aeruginosins, microginin and their mixtures with microcystin and cylindrospermopsin on aquatic plant physiology: An experimental approach

Cyanobacteria produce a variety of oligopeptides beyond microcystins and other metabolites. Their biological activities are not fully recognized especially to aquatic plants. Acute toxicity tests on Spirodela polyrhiza and Lemna minor exposed to a range of concentrations of cyanobacterial metabolites: anabaenopeptins (ANA-A, ANA-B), aeruginosins 98 (Aer-A, Aer-B), microginin-FR1 (MG-FR1), microcystin-LR (MC-LR) and cylindrospermopsin (Cyl) were carried out to compare their influence on plant physiology. Effects of their binary mixtures were determined by isobole approach and calculation of the combination index (CI) that indicates a type of metabolites' interaction. Cyclic oligopeptides microcystin-LR and anabaenopeptin-A revealed the strongest inhibition of S. polyrhiza growth while other metabolites appeared less toxic. Oxygen evolution was inhibited by Cyl, MC-LR, ANA-A, ANA-B, while both variants of aeruginosins and MG-FR1 did not affect this process. Photosynthetic pigments' contents decreased in S. polyrhiza exposed to ANA-A and Cyl, while MC-LR and Aer-A caused their slight increase. 96 h-EC50 values showed that the growth of L. minor was more sensitive to MC-LR, ANA-A, MG-FR1 and Cyl than the growth of S. polyrhiza. In S. polyrhiza synergistic effects of all the binary mixtures of peptides with MC-LR on oxygen evolution were observed, while antagonistic one on the growth of S. polyrhiza exposed to the mixtures with aeruginosins and ANA-A. The mixtures of MC-LR and MG-FR1 with cylindrospermopsin revealed synergistic effects on the growth but antagonistic one to the O2 evolution. Quadruple mixtures (ANA-A + MC-LR + MG-FR1+Cyl) did not reveal any inhibitive effect on the plant growth and very slight on the oxygen evolution, irrespectively of their total concentrations. Various effects caused by ANA-A and ANA-B suggest the importance of molecule structures of metabolites for toxicity. Composition of the mixtures of cyanobacterial metabolites was essential for the observed effects.