Using backbone-cyclized Cys-rich polypeptides as molecular scaffolds to target protein–protein interactions

Abstract

The use of disulfide-rich backbone-cyclized polypeptides, as molecular scaffolds to design a new generation of bioimaging tools and drugs that are potent and specific, and thus might have fewer side effects than traditional small-molecule drugs, is gaining increasing interest among the scientific and in the pharmaceutical industries. Highly constrained macrocyclic polypeptides are exceptionally more stable to chemical, thermal and biological degradation and show better biological activity when compared with their linear counterparts. Many of these relatively new scaffolds have been also found to be highly tolerant to sequence variability, aside from the conserved residues forming the disulfide bonds, able to cross cellular membranes and modulate intracellular protein–protein interactions both in vitro and in vivo. These properties make them ideal tools for many biotechnological applications. The present study provides an overview of the new developments on the use of several disulfide-rich backbone-cyclized polypeptides, including cyclotides, θ-defensins and sunflower trypsin inhibitor peptides, in the development of novel bioimaging reagents and therapeutic leads.

Discovery of Cyclotides from Australasian Plants

“…[61] Their exceptional stability, engendered by the CCK motif has led to their applications as stable scaffolds for drug design. [62][63][64][65][66][67][68][69] Cyclotides are present in many plants as a natural defence against insects and other pests, [70,71] and one plant may contain anywhere from just a few, to a few hundred different cyclotides. [72] Figure 1 shows a schematic representation of the prototypic cyclotide, kalata B1, originally discovered in the course of investigations of the medicinal uses of the African plant Oldenlandia affinis.…”

“…Cyclotides have been extensively reviewed in the past [62][63][64][65][66][67][68][69][82][83][84][85][86][87][88][89][90][91] and readers are referred to some of these articles and a recent book [92] for a more detailed background on their discovery, biosynthesis and applications. In the current article our focus is on just those plants that grow in Australasia and are thus accessible to researchers in the region.…”

“…One way of illustrating this phenomenon via noting the variation in size and amino acid content of each of the six backbone loops. Table 3 This topic has been reviewed extensively [62][63][64][65][66][67][68][69] and there are now more than two dozen examples of grafted cyclotides targeting a wide range of diseases, including cardiovascular disease, cancer, pain, infectious and inflammatory disease. Solid phase peptide chemistry has underpinned many of these applications and we have been fortunate to have benefitted from the outstanding facilities and training provided at The University of Queensland by Paul Alewood.…”

The Potential of the Cyclotide Scaffold for Drug Development

“…The unique properties associated with the cyclotide scaffold make it an excellent molecular framework for the design of a novel type of peptide-based therapeutics (see Table 1) [17,18,21,22]. Cyclotides are extremely resistant to physical, chemical, and biological degradation due to the highly rigid and compact structure provided by the CCK topology.…”

“…Special attention has been recently given to the use of highly constrained polypeptides for the development of novel stable polypeptide-based therapeutics [17,18,19]. Cyclotides are a fascinating emerging family of large plant-derived backbone-cyclized polypeptides (≈30–40 amino acids long) containing a 3 disulfide-stabilized core characterized by an unusual knotted structure (Figure 1) [20].…”