Pseudomonas CLiPs are ubiquitous specialized metabolites, impacting the producer’s lifestyle and interactions with the (a)biotic environment. Consequently, they generate interest for agricultural and clinical applications.

Cyclic lipodepsipeptides or CLiPs from Pseudomonas are secondary metabolites that mediate a wide range of biological functions for their producers, and display antimicrobial and anticancer activities. Direct interaction of CLiPs with the cellular membranes is presumed to be essential in causing these. To understand the processes involved at the molecular level, knowledge of the conformation and dynamics of CLiPs at the water-lipid interface is required to guide the interpretation of biophysical investigations in model membrane systems. We used NMR and molecular dynamics to study the conformation, location and orientation of the Pseudomonas CLiP viscosinamide in a water/dodecylphosphocholine solution. In the process, we demonstrate the strong added value of combining uniform, isotope-enriched viscosinamide and protein NMR methods. In particular, the use of techniques to determine backbone dihedral angles and detect and identify long-lived hydrogen bonds, establishes that the solution conformation previously determined in acetonitrile is maintained in water/dodecylphosphocholine solution. Paramagnetic relaxation enhancements pinpoint viscosinamide near the water-lipid interface, with its orientation dictated by the amphipathic distribution of hydrophobic and hydrophilic residues. Finally, the experimental observations are supported by molecular dynamics simulations. Thus a firm structural basis is now available for interpreting biophysical and bioactivity data relating to this class of compounds.

Long-range intramolecular vibrational energy redistribution (IVR) driven conformational changes were investigated in a matrix-isolated open-chain, asymmetrical dicarboxylic acid, E-glutaconic acid. Although the analysis was challenging due to the presence of multiple backbone conformers and short lifetimes of the prepared higher energy cis conformers, it was shown that the selective excitation of the O–H stretching overtone of one of the carboxylic groups can induce the conformational change (trans to cis) of the other carboxylic group, located at the other end of the E-glutaconic acid molecule. This is a direct proof that the IVR process can act through eight covalent bonds in a flexible molecule before the excess energy completely dissipates into the matrix. The lifetime of the prepared higher energy conformers (averaged over the different backbones) was measured to be 12 s.

The emergence of a peculiar molecular phenomenon, the single-centered, but multiple Lewis acidity, is uncovered among Lewis acidic boranes with appropriate steric crowding and symmetry design.

Cyclic lipopeptides (CLiPs) are secondary metabolites secreted by a range of bacterial phyla. CLiPs from Pseudomonas in particular display diverse structural variations in terms of the number of amino acid residues, macrocycle size, amino acid identity and stereochemistry (e.g. D- vs. L-amino acids). Reports detailing the discovery of novel or already characterized CLiPs from new sources appear regularly in literature. Increasingly however, the lack of detailed characterization threatens to cause considerable confusion, especially if configurational heterogeneity is present for one or more amino acids. Using Pseudomonas CLiPs from the Bananamide, Orfamide and Xantholysin groups as test cases, we demonstrate and validate that ¹ H and ¹³ C NMR chemical shifts of CLiPs are sufficiently sensitive to differentiate between possible diastereomers of a particular sequence even when they only differ in a single D/L configuration. Rapid screening, involving simple comparison of the NMR fingerprint of a newly isolated CLiP with that of a reference CLiP of known stereochemistry, can then be applied to resolve dead-ends in configurational characterization and avoid the much more cumbersome chemical characterization protocols. Even when the stereochemistry of a particular reference CLiP remains to be established, NMR fingerprinting still allows verifying whether a CLiP from a novel source is already present in the reference collection, thus contributing to dereplication. To benefit research involving CLiPs, we have made a publicly available ‘knowledge base’ at https://www.rhizoclip.be , where we present an overview of published NMR fingerprint data of characterized CLiPs, together with literature data on the originally determined structures. Significance Statement: Pseudomonas CLiPs, are ubiquitous specialized metabolites, impacting the producer’s lifestyle and interactions with the (a)biotic environment. Consequently, they generate interest for agricultural and clinical applications. Establishing structure-activity relationships as premise to their development is hindered because full structural characterization including stereochemistry requires labor-intensive analyses, without guarantee for success. Moreover, increasing use of superficial comparison with previously characterized CLiPs introduces or propagates erroneous attributions, clouding further scientific progress. We provide a generally applicable characterization methodology for structural comparison of newly isolated CLiPs to reference compounds with (un)known stereochemistry based on NMR fingerprints. The reference compound database available for the wide scientific community promises to facilitate structural assessment and dereplication of newly isolated CLiPs, and to support genome mining for novel CLiPs.

Electronic proceedings of IJCAI 2022