Through-space transfer of chiral information mediated by a plasmonic nanomaterial

The ability to detect chirality gives stereochemically attuned nanosensors the potential to revolutionise the study of biomolecular processes. Such devices may structurally characterise the mechanisms of protein-ligand binding, the intermediates of amyloidogenic diseases and the effects of phosphorylation and glycosylation. We demonstrate that single nanoparticle plasmonic reporters, or nanotags, can enable a stereochemical response to be transmitted from a chiral analyte to an achiral benzotriazole dye molecule in the vicinity of a plasmon resonance from an achiral metallic nanostructure. The transfer of chirality was verified by the measurement of mirror image surface enhanced resonance Raman optical activity spectra for the two enantiomers of each of ribose and tryptophan. Computational modelling confirms these observations and reveals the novel chirality transfer mechanism responsible. This is the first report of colloidal metal nanoparticles in the form of single plasmonic substrates displaying an intrinsic chiral sensitivity once attached to a chiral molecule

Reduced Sweetness of a Monellin (MNEI) Mutant Results from Increased Protein Flexibility and Disruption of a Distant Poly-(L-Proline) II Helix

Monellin is a highly potent sweet-tasting protein but relatively little is known about how it interacts with the sweet taste receptor. We determined X-ray crystal structures of 3 single-chain monellin (MNEI) proteins with alterations at 2 core residues (G16A, V37A, and G16A/V37A) that induce 2- to 10-fold reductions in sweetness relative to the wild-type protein. Surprisingly, no changes were observed in the global protein fold or the positions of surface amino acids important for MNEI sweetness that could explain these differences in protein activity. Differential scanning calorimetry showed that while the thermal stability of each mutant MNEI was reduced, the least sweet mutant, G16A-MNEI, was not the least stable protein. In contrast, solution spectroscopic measurements revealed that changes in protein flexibility and the C-terminal structure correlate directly with protein activity. G16A mutation-induced disorder in the protein core is propagated via changes to hydrophobic interactions that disrupt the formation and/or position of a critical C-terminal poly-(L-proline) II helix. These findings suggest that MNEI interaction with the sweet taste receptor is highly sensitive to the relative positions of key residues across its protein surface and that loss of sweetness in G16A-MNEI may result from an increased entropic cost of binding

Carbohydrate secondary and tertiary structure using raman spectroscopy

Raman spectroscopy is a long-established analytical technique that has now proliferated into a variety of research tools that are able to identify and characterize almost any type of molecule under most conditions. As such, Raman spectroscopies are well suited to the study of carbohydrates, from simple monosaccharides to the largest glycosaminoglycans and from industrial bioreactors to in situ measurements on living cells. This review covers a range of examples of how Raman techniques are addressing the questions of glycobiologists working on diverse aspects of this fascinating but poorly understood class of biomolecules. Focus is placed on the application of Raman, surface-enhanced Raman, Raman optical activity, and related spectroscopies to characterizing carbohydrates of all types, with only a general introduction to the theory of the techniques themselves. Particular attention is also paid to the computational tools now regularly used by spectroscopists to analyze complex data. Although this review is aimed at the glycobiology community, the examples discussed also demonstrate to the expert spectroscopist how their techniques can impact on the exciting opportunities presented by working with carbohydrates