No abstract

Daptomycin is an acidic lipopeptide antibiotic, whose three-dimensional structure and mechanism of action is currently unknown. Recently daptomycin, trade name Cubicin, was approved as a drug for the treatment of skin-related infections (M. Larkin Lancet, 2003, 3, 677) and became the first antibiotic of its class to be used in the clinic (A. Raja et al., Nature Rev. Drug Discov., 2003, 2, 943-944). We have carried out a systematic high field NMR study of daptomycin and its binding to calcium ions which is essential for antibiotic activity. In this first report, we demonstrate the sequence-specific resonance assignment of daptomycin under resolved NMR measurement conditions. In addition to this, we have determined the 3D structure of apo-daptomycin and demonstrated a 1 : 1 stoichiometry on the binding to calcium ions. We have also demonstrated that the binding of calcium ions does not result in major conformational changes, but does induce aggregation. This may be an important factor in the mode of action of daptomycin.

While many compounds have been reported to change in laboratory based drought-stress experiments, little is known about how such compounds change, and are significant, under field conditions. The Pisum sativum L. (pea) leaf metabolome has been profiled, using 1D and 2D NMR spectroscopy, to monitor the changes induced by drought-stress, under both glasshouse and simulated field conditions. Significant changes in resonances were attributed to a range of compounds, identified as both primary and secondary metabolites, highlighting metabolic pathways that are stress-responsive. Importantly, these effects were largely consistent among different experiments with highly diverse conditions. The metabolites that were present at significantly higher concentrations in droughtstressed plants under all growth conditions included proline, valine, threonine, homoserine, myoinositol, c-aminobutyrate (GABA) and trigonelline (nicotinic acid betaine). Metabolites that were altered in relative amounts in different experiments, but not specifically associated with drought-stress, were also identified. These included glutamate, asparagine and malate, with the last being present at up to 5-fold higher concentrations in plants grown in field experiments. Such changes may be expected to impact both on plant performance and crop end-use.

Background: NMR targeted and untargeted methodologies are widely recognized as important tools for food authentication and the detection of counterfeit products. Targeted approaches allow the identification of specific markers of identity/adulteration for a given foodstuff. In the untargeted approach, the chemical profile of the whole foodstuff is used to create a unique fingerprint as a reference for suspect samples. The untargeted analysis methodology typically follows the metabolomics approach. Scope and approach: In this manuscript we discuss how both targeted and untargeted NMR methodologies are applied in routine use for food fraud monitoring. The cost-effective approaches for routine application are discussed using examples of Food Screener™ and benchtop low-field instruments. Key findings and conclusions: Several examples of routine consolidated NMR targeted and untargeted applications are reported and the food matrices that are problematic for the NMR application are discussed. The future NMR implementation into routine practice will rely on the further exploration of FoodScreener™ like platforms for simultaneous targeted and untargeted applications and the continued development of applications for low-field benchtop instrumentation.

No abstract