β-Sheet 13C structuring shifts appear only at the H-bonded sites of hairpins

Design of monomeric water-soluble β-hairpin and β-sheet peptides

Since the first report in 1993 (JACS 115, 5887-5888) of a peptide able to form a monomeric β-hairpin structure in aqueous solution, the design of peptides forming either β-hairpins (two-stranded antiparallel β-sheets) or three-stranded antiparallel β-sheets has become a field of growing interest and activity. These studies have yielded great insights into the principles governing the stability and folding of β-hairpins and antiparallel β-sheets. This chapter provides an overview of the reported β-hairpin/β-sheet peptides focussed on the applied design criteria, reviews briefly the factors contributing to β-hairpin/β-sheet stability, and describes a protocol for the de novo design of β-sheet-forming peptides based on them. Guidelines to select appropriate turn and strand residues and to avoid self-association are provided. The methods employed to check the success of new designed peptides are also summarized. Since NMR is the best technique to that end, NOEs and chemical shifts characteristic of β-hairpins and three-stranded antiparallel β-sheets are given.

13C structuring shifts for the analysis of model β-hairpins and β-sheets in proteins: diagnostic shifts appear only at the cross-strand H-bonded residues

The present studies have shown that (13)C=O, (13)C(α) and (13)C(β) of H-bonded strand residues in β-hairpins provide additional probes for quantitating the extent of folding in β-hairpins and other β-sheet models. Large differences in the structuring shifts (CSDs) of these (13)C sites in H-bonded versus non-H-bonded sites are observed: the differences between H-bonded and non-H-bonded sites are greater than 1.2 ppm for all three (13)C probes. This prompts us to suggest that efforts to determine the extent of hairpin folding from (13)C shifts should be based exclusively on the observation at the cross-strand H-bonded sites. Furthermore, the statistics suggest the (13)C' and (13)C(β) CSDs will provide the best differentiation with 100%-folded CSD values approaching -2.6 and +3 ppm, respectively, for the H-bonded sites. These conclusions can be extended to edge-strands of protein β-sheets. Our survey of reported (13)C shifts in β-proteins indicates that some of the currently employed random coil values need to be adjusted, particularly for ionization-induced effects.

Synthetic virus-like particles and conformationally constrained peptidomimetics in vaccine design

Conformationally constrained peptidomimetics could be of great value in the design of vaccines targeting protective epitopes on viral and bacterial pathogens. But the poor immunogenicity of small synthetic molecules represents a serious obstacle for their use in vaccine development. Here, we show how a constrained epitope mimetic can be rendered highly immunogenic through multivalent display on the surface of synthetic virus-like nanoparticles. The target epitope is the V3 loop from the gp120 glycoprotein of HIV-1 bound to the neutralizing antibody F425-B4e8. The antibody-bound V3 loop adopts a β-hairpin conformation, which is effectively stabilized by transplantation onto a D-Pro-L-Pro template. The resulting mimetic after coupling to synthetic virus-like particles elicited antibodies in rabbits that recognized recombinant gp120. The elicited antibodies also blocked infection by the neutralization sensitive tier-1 strain MN of HIV-1, as well as engineered viruses with the V1V2 loop deleted; this result is consistent with screening of V3 by the V1V2 loop in intact trimeric viral gp120 spikes. The results provide new insights into HIV-1 vaccine design based on the V3 loop, and illustrate how knowledge from structural biology can be exploited for the design of constrained epitope mimetics, which can be delivered to the immune system by using a highly immunogenic synthetic nanoparticle delivery system.