Relationship between side-chain branching and stoichiometry in ß(3)-peptide bundles.

The stability and stoichiometry of ß(3)-peptide bundles is influenced by side-chain identity. ß(3)-peptides containing ß(3)-homoleucine on one helical face assemble into octamers, whereas those containing ß(3)-homovaline form tetramers. From a structural perspective, the side chains of ß(3)-homoleucine and ß(3)-homovaline differ in terms of both side-chain length and γ-carbon branching. To evaluate the extent to which these two parameters control ß(3)-peptide bundle stoichiometry, we synthesized the ß(3)-peptide Acid-3Y, which contains ß(3)-homoisoleucine in place of ß(3)-homoleucine or ß(3)-homovaline. Acid-3Y assembles into a stable tetramer whose stability resembles that of the previously characterized Acid-VY tetramer. These results suggest that ß(3)-peptide bundle stoichiometry is dominated by the presence or absence of γ-carbon branching on core side chains.

Enhancing ß3 -peptide bundle stability by design.

We reported recently that certain ß(3) -peptides self-assemble in aqueous solution into discrete bundles of unique structure and defined stoichiometry. The first ß-peptide bundle reported was the octameric Zwit-1F, whose fold is characterized by a well-packed, leucine-rich core and a salt-bridge-rich surface. Close inspection of the Zwit-1F structure revealed four nonideal interhelical salt-bridge interactions whose heavy atom-heavy atom distances were longer than found in natural proteins of known structure. Here we demonstrate that the thermodynamic stability of a ß-peptide bundle can be enhanced by optimizing the length of these four interhelical salt bridges. Combined with previous work on the role of internal packing residues, these results provide another critical step in the "bottom-up" formation of ß-peptide assemblies with defined sizes, reproducible structures, and sophisticated function.

Bridged beta(3)-peptide inhibitors of p53-hDM2 complexation: correlation between affinity and cell permeability.

Beta-peptides possess several features that are desirable in peptidomimetics; they are easily synthesized, fold into stable secondary structures in physiologic buffers, and resist proteolysis. They can also bind to a diverse array of proteins to inhibit their interactions with alpha-helical ligands. beta-peptides are usually not cell-permeable, however, and this feature limits their utility as research tools and potential therapeutics. Appending an Arg(8) sequence to a beta-peptide improves uptake but adds considerable mass. We previously reported that embedding a small cationic patch within a PPII, alpha-, or beta-peptide helix improves uptake without the addition of significant mass. In another mass-neutral strategy, Verdine, Walensky, and others have reported that insertion of a hydrocarbon bridge between the i and i + 4 positions of an alpha-helix also increases cell uptake. Here we describe a series of beta-peptides containing diether and hydrocarbon bridges and compare them on the basis of cell uptake and localization, affinities for hDM2, and 14-helix structure. Our results highlight the relative merits of the cationic-patch and hydrophobic-bridge strategies for improving beta-peptide uptake and identify a surprising correlation between uptake efficiency and hDM2 affinity.

Beta-peptide bundles with fluorous cores.

We reported recently that certain beta-peptides self-assemble spontaneously into cooperatively folded bundles whose kinetic and thermodynamic metrics mirror those of natural helix bundle proteins. The structures of four such beta-peptide bundles are known in atomic detail. These structures reveal a solvent-sequestered, hydrophobic core stabilized by a unique arrangement of leucine side chains and backbone methylene groups. Here we report that this hydrophobic core can be re-engineered to contain a fluorous subdomain while maintaining the characteristic beta-peptide bundle fold. Like alpha-helical bundles possessing fluorous cores, fluorous beta-peptide bundles are stabilized relative to hydrocarbon analogues and undergo cold denaturation. Beta-peptide bundles with fluorous cores represent the essential first step in the synthesis of orthogonal protein assemblies that can sequester selectively in an interstitial membrane environment.

Sophistication of foldamer form and function in vitro and in vivo.

Advances in the foldamer field in recent years are as diverse as the backbones of which they are composed. Applications have ranged from cellular penetration and membrane disruption to discrete molecular recognition, while efforts to control the complex geometric shape of foldamers has entered the realm of tertiary and quaternary structure. This review will provide recent examples of progress in the foldamer field, highlighting the significance of this class of compounds and the advances that have been made towards exploiting their full potential.

A ß-peptide agonist of the GLP-1 receptor, a class B GPCR.

Previous work has shown that certain ß(3)-peptides can effectively mimic the side chain display of an α-helix and inhibit interactions between proteins, both in vitro and in cultured cells. Here we describe a ß(3)-peptide analog of GLP-1, CC-3(Act), that interacts with the GLP-1R extracellular domain (nGLP-1R) in vitro in a manner that competes with exendin-4 and induces GLP-1R-dependent cAMP signaling in cultured CHO-K1 cells expressing GLP-1R.