The Cyclic Cystine Ladder of Theta‐Defensins as a Stable, Bifunctional Scaffold: A Proof‐of‐Concept Study Using the Integrin‐Binding RGD Motif.

Abstract

Peptides have the specificity and size required to target the protein-protein interactions involved in many diseases. Some cyclic peptides have been utilised as scaffolds for peptide drugs because of their stability; however, other cyclic peptide scaffolds remain to be explored. θ-Defensins are cyclic peptides from mammals; they are characterised by a cyclic cystine ladder motif and have low haemolytic and cytotoxic activity. Here we demonstrate the potential of the cyclic cystine ladder as a scaffold for peptide drug design by introducing the integrin-binding Arg-Gly-Asp (RGD) motif into the θ-defensin RTD-1. The most active analogue had an IC50 of 18 nM for the αv β3 integrin as well as high serum stability, thus demonstrating that a desired bioactivity can be imparted to the cyclic cystine ladder. This study highlights how θ-defensins can provide a stable and conformationally restrained scaffold for bioactive epitopes in a β-strand or turn conformation. Furthermore, the symmetry of the cyclic cystine ladder presents the opportunity to design peptides with dual bioactive epitopes to increase activity and specificity.

The Chemistry and Biology of Theta Defensins

“…The structures comprise two highly constrained β‐strands joined by β1′ turns, and heteronuclear NOEs and predicted order parameters suggested that θ‐defensins are more rigid than previously thought 7. Several structures of θ‐defensins are now available in the Protein Data Bank for modeling and peptide design applications 76. 77…”

Structure‐Based Design of Inhibitors of Protein–Protein Interactions: Mimicking Peptide Binding Epitopes

“…[45] Another naturally inspired cyclization strategy to afford bioactive PPI inhibitors involves the incorporation of binding motifs into the so-called cysteine ladders, which appear in q-defensins as a parallel arrangement of disulfide bonds that stabilize a turn structure. [46] Alternatively, peptide epitopes have been grafted onto lasso peptides, thus allowing their preorganization into bioactive conformations. [47] These genetically encoded peptides form a macrocycle with their C-terminal tail passing through this ring system.…”

“…[67] An alternative approach to constrain the RGD sequence is its incorporation into the so-called "cysteine ladder" peptides. [46] These naturally occurring cyclic peptides compose several disulfide bridges arranged in a parallel fashion. In addition to the RGD sequence, integrin receptors can recognize the LDV turn structure.…”

Neue Modalitäten für schwierige Zielstrukturen in der Wirkstoffentwicklung

“…Außer fürCyclotide wurde das Aufpfropfkonzept auch für Conotoxin-, [98] SFTI-1- [99] und q-Defensin-Gerüststrukturen [100] angewendet, um Inhibitoren von Proteasen, Wachstumsfaktoren, GPCRs,K inasen und PPIs herzustellen. [99,101] …”