Substrate Trapping in the Siderophore Tailoring Enzyme PvdQ

Biosynthesis and engineering of the nonribosomal peptides with a C-terminal putrescine

The broad bioactivities of nonribosomal peptides rely on increasing structural diversity. Genome mining of the Burkholderiales strain Schlegelella brevitalea DSM 7029 leads to the identification of a class of dodecapeptides, glidonins, that feature diverse N-terminal modifications and a uniform putrescine moiety at the C-terminus. The N-terminal diversity originates from the wide substrate selectivity of the initiation module. The C-terminal putrescine moiety is introduced by the unusual termination module 13, the condensation domain directly catalyzes the assembly of putrescine into the peptidyl backbone, and other domains are essential for stabilizing the protein structure. Swapping of this module to another two nonribosomal peptide synthetases leads to the addition of a putrescine to the C-terminus of related nonribosomal peptides, improving their hydrophilicity and bioactivity. This study elucidates the mechanism for putrescine addition and provides further insights to generate diverse and improved nonribosomal peptides by introducing a C-terminal putrescine.

Discovery of chromene compounds as inhibitors of PvdQ acylase of Pseudomonas aeruginosa

The acquisition of iron is a crucial mechanism for the survival of pathogenic bacteria such as Pseudomonas aeruginosa in eukaryotic hosts. The key iron chelator in this organism is the siderophore pyoverdine, which was shown to be crucial for iron homeostasis. Pyoverdine is a non-ribosomal peptide with several maturation steps in the cytoplasm and others in the periplasmatic space. A key enzyme for its maturation is the acylase PvdQ. The inhibition of PvdQ stops the maturation of pyoverdine causing a significant imbalance in the iron homeostasis and hence can negatively influence the survival of P. aeruginosa. In this work, we successfully synthesized chromene-derived inhibitory molecules targeting PvdQ in a low micromolar range. In silico modeling as well as kinetic evaluations of the inhibitors suggest a competitive inhibition of the PvdQ function. Further, we evaluated the inhibitor in vivo on P. aeruginosa cells and report a dose-dependent reduction of pyoverdine formation. The compound also showed a protecting effect in a Galleria mellonella infection model.

The biosynthesis of pyoverdines

Pyoverdines are fluorescent siderophores of pseudomonads that play important roles for growth under iron-limiting conditions. The production of pyoverdines by fluorescent pseudomonads permits their colonization of hosts ranging from humans to plants. Prominent examples include pathogenic or non-pathogenic species such as Pseudomonas aeruginosa, P. putida, P. syringae, or P. fluorescens. Many distinct pyoverdines have been identified, all of which have a dihydroxyquinoline fluorophore in common, derived from oxidative cyclizations of non-ribosomal peptides. These serve as precursor of pyoverdines and are commonly known as ferribactins. Ferribactins of distinct species or even strains often differ in their sequence, resulting in a large variety of pyoverdines. However, synthesis of all ferribactins begins with an L-Glu/D-Tyr/L-Dab sequence, and the fluorophore is generated from the D-Tyr/L-Dab residues. In addition, the initial L-Glu residue is modified to various acids and amides that are responsible for the range of distinguishable pyoverdines in individual strains. While ferribactin synthesis is a cytoplasmic process, the maturation to the fluorescent pyoverdine as well as the tailoring of the initial glutamate are exclusively periplasmic processes that have been a mystery until recently. Here we review the current knowledge of pyoverdine biosynthesis with a focus on the recent advancements regarding the periplasmic maturation and tailoring reactions.

Nonribosomal peptide synthetase biosynthetic clusters of ESKAPE pathogens

Covering: up to 2017.Natural products are important secondary metabolites produced by bacterial and fungal species that play important roles in cellular growth and signaling, nutrient acquisition, intra- and interspecies communication, and virulence. A subset of natural products is produced by nonribosomal peptide synthetases (NRPSs), a family of large, modular enzymes that function in an assembly line fashion. Because of the pharmaceutical activity of many NRPS products, much effort has gone into the exploration of their biosynthetic pathways and the diverse products they make. Many interesting NRPS pathways have been identified and characterized from both terrestrial and marine bacterial sources. Recently, several NRPS pathways in human commensal bacterial species have been identified that produce molecules with antibiotic activity, suggesting another source of interesting NRPS pathways may be the commensal and pathogenic bacteria that live on the human body. The ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) have been identified as a significant cause of human bacterial infections that are frequently multidrug resistant. The emerging resistance profile of these organisms has prompted calls from multiple international agencies to identify novel antibacterial targets and develop new approaches to treat infections from ESKAPE pathogens. Each of these species contains several NRPS biosynthetic gene clusters. While some have been well characterized and produce known natural products with important biological roles in microbial physiology, others have yet to be investigated. This review catalogs the NRPS pathways of ESKAPE pathogens. The exploration of novel NRPS products may lead to a better understanding of the chemical communication used by human pathogens and potentially to the discovery of novel therapeutic approaches.

Synthesis of benzo[6]urils and their selective interactions with bipyridines

Benzo[6]urils bearing hydroxymethyl or methyl groups have been synthesized with a facile method, and their supramolecular interactions with bipyridine guests have been investigated.