Repurposed inhibitor of bacterial dihydrodipicolinate reductase exhibits effective herbicidal activity.

Herbicide resistance represents one of the biggest threats to our natural environment and agricultural sector. Thus, new herbicides are urgently needed to tackle the rise in herbicide-resistant weeds. Here, we employed a novel strategy to repurpose a 'failed' antibiotic into a new and target-specific herbicidal compound. Specifically, we identified an inhibitor of bacterial dihydrodipicolinate reductase (DHDPR), an enzyme involved in lysine biosynthesis in plants and bacteria, that exhibited no antibacterial activity but severely attenuated germination of the plant Arabidopsis thaliana. We confirmed that the inhibitor targets plant DHDPR orthologues in vitro, and exhibits no toxic effects against human cell lines. A series of analogues were then synthesised with improved efficacy in germination assays and against soil-grown A. thaliana. We also showed that our lead compound is the first lysine biosynthesis inhibitor with activity against both monocotyledonous and dicotyledonous weed species, by demonstrating its effectiveness at reducing the germination and growth of Lolium rigidum (rigid ryegrass) and Raphanus raphanistrum (wild radish). These results provide proof-of-concept that DHDPR inhibition may represent a much-needed new herbicide mode of action. Furthermore, this study exemplifies the untapped potential of repurposing 'failed' antibiotic scaffolds to fast-track the development of herbicide candidates targeting the respective plant enzymes.

Structural insight into the Scribble PDZ domains interaction with the oncogenic Human T-cell lymphotrophic virus-1 (HTLV-1) Tax1 PBM.

Scribble (Scrib) is a highly conserved cell polarity regulator that harbours potent tumour suppressor activity and plays an important role in cell migration. Dysregulation of polarity is associated with poor prognosis during viral infections. Human T-cell lymphotrophic virus-1 (HTLV-1) encodes for the oncogenic Tax1 protein, a modulator of the transcription of viral and human proteins that can cause cell cycle dysregulation as well as a loss of genomic integrity. Previous studies established that Scribble interacts with Tax1 via its C-terminal PDZ-binding motif (PBM), leading to aggregation of polarity regulators and subsequent perturbation of host cell adhesion, proliferation, and signalling. Using isothermal titration calorimetry, we now show that all four PDZ domains of Scribble bind to Tax1 PBM. We then determined crystal structures of Scribble PDZ1, PDZ2 and PDZ3 domains bound to Tax1 PBM. Our findings establish a structural basis for Tax1-mediated subversion of Scribble-mediated cell polarity signalling and provide the platform for mechanistic studies to examine Tax1 induced mislocalization of Scribble and the associated changes in cellular architecture and subsequent tumorigenesis.

Structural characterisation of a MAPR-related archaeal cytochrome b5M protein.

We recently reported that the membrane-associated progesterone receptor (MAPR) protein family (mammalian members: PGRMC1, PGRMC2, NEUFC and NENF) originated from a new class of prokaryotic cytochrome b5 (cytb5 ) domain proteins, called cytb5M (MAPR-like). Relative to classical cytb5 proteins, MAPR and ctyb5M proteins shared unique sequence elements and a distinct heme-binding orientation at an approximately 90° rotation relative to classical cytb5 , as demonstrated in the archetypal crystal structure of a cytb5M protein (PDB accession number 6NZX). Here, we present the crystal structure of an archaeal cytb5M domain (Methanococcoides burtonii WP_011499504.1, PDB:6VZ6). It exhibits similar heme binding to the 6NZX cytb5M , supporting the deduction that MAPR-like heme orientation was inherited from the prokaryotic ancestor of the original eukaryotic MAPR gene.

A dual-target herbicidal inhibitor of lysine biosynthesis.

Herbicides with novel modes of action are urgently needed to safeguard global agricultural industries against the damaging effects of herbicide-resistant weeds. We recently developed the first herbicidal inhibitors of lysine biosynthesis, which provided proof-of-concept for a promising novel herbicide target. In this study, we expanded upon our understanding of the mode of action of herbicidal lysine biosynthesis inhibitors. We previously postulated that these inhibitors may act as proherbicides. Here, we show this is not the case. We report an additional mode of action of these inhibitors, through their inhibition of a second lysine biosynthesis enzyme, and investigate the molecular determinants of inhibition. Furthermore, we extend our herbicidal activity analyses to include a weed species of global significance.

Structural and biochemical analyses of concanavalin A circular permutation by jack bean asparaginyl endopeptidase.

Over 30 years ago, an intriguing posttranslational modification was found responsible for creating concanavalin A (conA), a carbohydrate-binding protein from jack bean (Canavalia ensiformis) seeds and a common carbohydrate chromatography reagent. ConA biosynthesis involves what was then an unprecedented rearrangement in amino-acid sequence, whereby the N-terminal half of the gene-encoded conA precursor (pro-conA) is swapped to become the C-terminal half of conA. Asparaginyl endopeptidase (AEP) was shown to be involved, but its mechanism was not fully elucidated. To understand the structural basis and consequences of circular permutation, we generated recombinant jack bean pro-conA plus jack bean AEP (CeAEP1) and solved crystal structures for each to 2.1 and 2.7 Å, respectively. By reconstituting conA biosynthesis in vitro, we prove CeAEP1 alone can perform both cleavage and cleavage-coupled transpeptidation to form conA. CeAEP1 structural analysis reveals how it is capable of carrying out both reactions. Biophysical assays illustrated that pro-conA is less stable than conA. This observation was explained by fewer intermolecular interactions between subunits in the pro-conA crystal structure and consistent with a difference in the prevalence for tetramerization in solution. These findings elucidate the consequences of circular permutation in the only posttranslation example known to occur in nature.

Synthesis, conformational analysis and antibacterial activity of Au(I)-Ag(I) and Au(I)-Hg(II) heterobimetallic N-heterocyclic carbene complexes.

A post-synthetic modification and metallation procedure has been used to prepare a family of heterobimetallic Au(i)-Ag(i) and Au(i)-Hg(ii) complexes featuring either symmetrical or asymmetrical bis-N-heterocyclic carbene ligands with methylene or ethylene linker groups. This synthetic approach is versatile and allows for the synthesis of heterobimetallic complexes bearing asymmetrical ligands that differ in the nature of the NHC wingtip substituents (dimethyl, diethyl or ethyl-methyl) and for the selective placement of the different metal ions. The synthesised complexes were characterised using 1H and 13C NMR spectroscopy and high resolution mass spectrometry (HR-MS) and in the case of complexes 4a, 5b and 8b by X-ray crystallography. The complexes of the methylene linked bridging ligands display conformational isomerism in solution and the conformations adopted by selected compounds were examined using variable temperature (VT) 1H NMR studies. The antibacterial properties of the heterobimetallic Au(i)-Ag(i) complexes in addition to the corresponding homobimetallic Ag(i)2, Au(i)2 complexes were evaluated against clinically relevant Gram-positive and Gram-negative bacterial strains. The homobimetallic Au(i)2 complex and precursor pro-ligand displayed no antibacterial activity up to 256 µg mL-1, whereas the homobimetallic Ag(i)2 was active against all Gram-positive and Gram-negative bacterial strains tested (MIC = 8-32 µg mL-1). Interestingly, both Au(i)-Ag(i) heterobimetallic complexes displayed similar broad-spectrum activity (MIC = 4-32 µg mL-1) to the Ag(i)2 homobimetallic complex.

Metal-Free Synthesis of Functional 1-Substituted-1,2,3-Triazoles from Ethenesulfonyl Fluoride and Organic Azides.

The boom in growth of 1,4-disubstituted triazole products, in particular, since the early 2000's, can be largely attributed to the birth of click chemistry and the discovery of the CuI -catalyzed azide-alkyne cycloaddition (CuAAC). Yet the synthesis of relatively simple, albeit important, 1-substituted-1,2,3-triazoles has been surprisingly more challenging. Reported here is a straightforward and scalable click-inspired protocol for the synthesis of 1-substituted-1,2,3-triazoles from organic azides and the bench stable acetylene surrogate ethenesulfonyl fluoride (ESF). The new transformation tolerates a wide selection of substrates and proceeds smoothly under metal-free conditions to give the products in excellent yield. Under controlled acidic conditions, the 1-substituted-1,2,3-triazole products undergo a Michael addition reaction with a second equivalent of ESF to give the unprecedented 1-substituted triazolium sulfonyl fluoride salts.