Stimuli-responsive Synthetic Metallopeptides

Abstract

Inspired by vital roles of metal ions as structure-stabilizing and regulating factors in biological systems, a great number of synthetic metallopeptides have been developed. This review focuses on metal-mediated stabilization and stimuli-responsive regulation of their secondary and higher-order structures by taking advantage of the characteristics of metal ions such as Lewis acidity, ligand-exchange ability, and redox properties. Ç IntroductionIn metal-including biomolecules such as metalloproteins or enzymes in living systems, metal ions play vital roles in molecular recognition, catalytic reaction, transportation, electron transfer, and structure stabilization or regulation.1 Focusing on a few examples of metal-mediated formation of higher-order structures of proteins, a typical example is zinc-finger proteins, which are composed of multiple finger units containing one Zn II ion bound by four coordinating side chains of His and/or Cys residues. The Zn II ions are well-known to stabilize the whole ternary structures and essential for DNA binding.2 In other cases, several metal ions such as Zn II , Cu II , and Fe III are considered a trigger for protein aggregations through interactions with some protein domains as seen in several brain disorders such as Alzheimer's disease and Parkinson's disease, 3 in which metal ions serve as inducers of protein folding or aggregation. On the other hand, metal ions in some proteins can regulate their higherorder structures through response to several stimuli, and the structural transformation is involved in protein functions. Hemoglobin is a typical example of such proteins, 4 that is a tetrameric protein in which O 2 trapping at the Fe II center of one heme unit induces the whole conformation change (T ¼ R transition) to achieve cooperative binding of molecular oxygens. One way to understand and further utilize such protein natures is a synthetic approach to stimuli-responsive mechanisms inspired by natural metalloproteins.For this purpose, design-based incorporation of metal binding sites into peptide structures has been extensively conducted. Synthetic peptides developed so far can be categorized as two types: (i) natural ¡-peptides possessing an optional sequence that can bind to metal ions through their coordinating functionalities of the residues or (ii) unnatural peptides containing synthetic amino acid residues whose side and/or main chains bind to metal ions. So far, many types of synthetic peptides have been reported based on both strategies, and the stabilization of secondary and higher-order structures of their metallopeptides has been demonstrated. Moreover, the metalmediated regulation of peptide structures has been recently studied based on the characteristics of metal ions such as Lewis acidity, ligand-exchange ability, and redox properties (Figure 1). This review describes the design outline of metallopeptides and then metal-mediated stabilization of ¡-helix and ¢-sheet structures taking a few basic examples of stimuli-responsive folding. The structu...

Metal-responsive structural transformation between artificial DNA duplexes and three-way junctions

“…Metal–ligand coordination is one of the most exploited molecular interactions to develop stimuli-responsive supermolecules and materials. 7 This is also the case for DNA architectures, in which a variety of interstrand metal complexes have been covalently incorporated. 8 Notable examples include the introduction of artificial metal-mediated base pairs into DNA duplexes.…”

Metal‐Coordinated Supramolecular Polymers from the Minimalistic Hybrid Peptide Foldamers

“…Metal‐triggered supramolecular assembly of peptides and proteins offers a promising platform for the creation of multifunctional materials. Along with the metal binding, natural amino acids such as His, Cys, Glu, Asp, etc., a variety of artificial ligands have been explored to design ordered supramolecular assemblies from short peptides [4a,b,d] . In addition, peptide coiled‐coils [5] and collagen triple helices [6] incorporated with metal binding ligands have been designed and studied.…”

Metal complexes of amino acids and peptides

“…334 Pt(II) complexes are probably the most studied among these metal containing species. Various enzymes are frequently used as cleaving agents of the peptide bonds but the catalytic activity of several metal complexes has also been well-known for a long time.…”