Modification of Poly(5,6-epoxy-l-norleucine) Gives Functional Polypeptides with Alternative Side-Chain Linkages

Sulfur Switches for Responsive Peptide Materials

There is considerable recent interest in the synthesis and development of peptide-based materials as mimics of natural biological assemblies that utilize proteins and peptides to form organized structures and develop beneficial properties. Due to their potential compatibility with living organisms, synthetic peptide materials are also being developed for applications such as cell grafting, therapeutic delivery, and implantable diagnostic devices. One desirable feature for such applications is the ability to design materials that can respond to stimuli by changes in their structure or properties under biologically relevant conditions. Peptide and protein assemblies can respond to stimuli, such as changes in temperature, solution pH, ions present in media, or interactions with other biomacromolecules. An exciting area of emerging research is focused on how biology uses the chemistry of sulfur-containing amino acids as a means to regulate biological processes. These concepts have been utilized and expanded in recent years to enable the development of peptide materials with readily switchable properties.The incorporation of sulfur atoms in polypeptides, peptides, and proteins provides unique sites that can be used to alter the physical and biological properties of these materials. Sulfur-containing amino acid residues, most often cysteine and methionine, are able to undergo a variety of selective chemical and enzyme-mediated reactions, which can be broadly characterized as redox or alkylation processes. These reactions often proceed under physiologically relevant conditions, can be reversible, and are significant in that they can alter residue polarity as well as conformations of peptide chains. These sulfur-based reactions are able to switch molecular and macromolecular properties of peptides and proteins in living systems and recently have been applied to synthetic peptide materials. Naturally occurring "sulfur switches" can be reversible or irreversible and are often triggered by enzymatic activity. Sulfur switches in peptide materials can also be triggered in vitro using oxidation/reduction and alkylation as well as photochemical reactions. The application of sulfur switches to peptide materials has greatly expanded the scope of these switches due to the ability to readily incorporate a wide variety of noncanonical sulfur-containing synthetic amino acids.Sulfur switches have been shown to provide considerable potential to reversibly alter peptide material properties under mild physiologically relevant conditions. An important molecular feature of sulfur-containing amino acid residues was found to be the location of sulfur atoms in the side chains. The variation of sulfur atom positions from the backbone by single bond lengths was found to significantly affect polypeptide chain conformations upon oxidation-reduction or alkylation/dealkylation reactions. With the successful adaptation of sulfur switches to peptide materials, future studies can explore how these switches affect how these materials interact with biological systems. This Account provides an overview of the different types of sulfur switch reactions found in biology and their properties and the elaboration of these switches in synthetic systems with a focus on recent developments and applications of reversible sulfur switches in peptide materials.

Effect of Modification Strategies on the Biological Activity of Peptides/Proteins

Covalent attachment of biologically active peptides/proteins with functional moieties is an effective strategy to control their biodistribution, pharmacokinetics, enzymatic digestion, and toxicity. This review focuses on the characteristics of different modification strategies and their effects on the biological activity of peptides/proteins and illustrates their relevant applications and potential.

Recent advances in post-polymerization modifications on polypeptides: synthesis and applications

Polypeptides, a kind of very promising biomaterial, have shown a wide range of applications due to their excellent biocompatibility, easy accessibility, and structural variability. To synthesize polypeptides with desired functions, post-polymerization modification (PPM) plays an important role in introducing novel chemical structure on their side-chains. The key of PPM strategy is to develop highly selective and efficient reactions that can couple the additional functional moieties with pre-installed side-chain functionalities on polypeptides. In this minireview, classic PPM reactions and especially their recent progresses are summarized, including different modification approaches for unsaturated alkyl group, oxygen-containing functional group, nitrogen-containing functional group, sulfur-containing functional group and other special functional group on side chains. In addition, this review also highlights the applications of structure-diversified polypeptides generated via PPM strategy in the field of biomaterial.

Versatile fully-substituted triazole-functionalized polypeptides with a stable α-helical conformation for gene delivery

A library of polypeptides bearing fully-substituted triazoles (FT) was developed via a Cu-catalyzed multicomponent reaction (MCR), which avoided the undesired hydrogen bonding and stabilized the α-helix in a broad pH range.

Ring opening polymerization of α-amino acids: advances in synthesis, architecture and applications of polypeptides and their hybrids

This review provides a comprehensive overview of the latest advances in the synthesis, architectural design and biomedical applications of polypeptides and their hybrids.