Activation of a Sweet Taste Receptor by Oleanane-Type Glycosides from Wisteria sinensis.

The phytochemical study of Wisteria sinensis (Sims) DC. (Fabaceae), commonly known as the Chinese Wisteria, led to the isolation of seven oleanane-type glycosides from an aqueous-ethanolic extract of the roots. Among the seven isolated saponins, two have never been reported before: 3-O-α-L-rhamnopyranosyl-(1→2)-ß-D-glucopyranosyl-(1→2)-ß-D-glucuronopyranosyl-22-O-acetylolean-12-ene-3ß,16ß,22ß,30-tetrol, and 3-O-ß-D-xylopyranosyl-(1→2)-ß-D-glucuronopyranosylwistariasapogenol A. Based on the close structures between the saponins from W. sinensis, and the glycyrrhizin from licorice, the stimulation of the sweet taste receptor TAS1R2/TAS1R3 by these glycosides was evaluated.

Folding in Place: Design of ß-Strap Motifs to Stabilize the Folding of Hairpins with Long Loops.

Despite their pivotal role in defining antibody affinity and protein function, ß-hairpins harboring long noncanonical loops remain synthetically challenging because of the large entropic penalty associated with their conformational folding. Little is known about the contribution and impact of stabilizing motifs on the folding of ß-hairpins with loops of variable length and plasticity. Here, we report a design of minimalist ß-straps (strap = strand + cap) that offset the entropic cost of long-loop folding. The judicious positioning of noncovalent interactions (hydrophobic cluster and salt-bridge) within the novel 8-mer ß-strap design RW(V/H)W···WVWE stabilizes hairpins with up to 10-residue loops of varying degrees of plasticity (Tm up to 52 °C; 88 ± 1% folded at 18 °C). This "hyper" thermostable ß-strap outperforms the previous gold-standard technology of ß-strand-ß-cap (16-mer) and provides a foundation for producing new classes of long hairpins as a viable and practical alternative to macrocyclic peptides.