Cyclotide Structures Revealed by NMR, with a Little Help from X‐ray Crystallography

Abstract

This review highlights the predominant role that NMR has had in determining the structures of cyclotides, a fascinating class of macrocyclic peptides found in plants. Cyclotides contain a cystine knot, a compact structural motif that is constrained by three disulfide bonds and able to resist chemical and biological degradation. Their resistance to proteolytic degradation has made cyclotides appealing as drug leads. Herein, we examine the developments that led to the identification and conclusive determination of the disulfide connectivity of cyclotides and describe in detail the structural features of exemplar cyclotides. We also review the role that X‐ray crystallography has played in resolving cyclotide structures and describe how racemic crystallography opened up the possibility of obtaining previously inaccessible X‐ray structures of cyclotides.

Tuning the Anti-Angiogenic Effect of the P15 Peptide Using Cyclic Trypsin Inhibitor Scaffolds

“…Based on the 1D data, the backbone amide proton peaks were well-dispersed indicating these peptides are well structured. 36,37 Figure 3A shows a comparison of secondary shifts for all P15 analogs and CIGB-300. Secondary αH shifts for the P15 epitope region are similar for all four peptides and fall within the range of −0.1 to +0.1 ppm, suggesting these peptides are in random coil conformation.…”

“…An analysis of secondary αH NMR chemical shifts is commonly used to predict peptide secondary structures. , Secondary shifts in this study were calculated based on the measured chemical shifts and the random coil values reported by Wishart et al NMR analyses of all peptides were compared to the native P15 epitope. Based on the 1D data, the backbone amide proton peaks were well-dispersed indicating these peptides are well structured. , Figure A shows a comparison of secondary shifts for all P15 analogs and CIGB-300. Secondary αH shifts for the P15 epitope region are similar for all four peptides and fall within the range of −0.1 to +0.1 ppm, suggesting these peptides are in random coil conformation.…”

One-Pot Cyclization to Large Peptidomimetic Macrocycles by In Situ-Generated β-Turn-Enforced Folding

“…It is noteworthy that, despite the difficulty in obtaining large quantities of single crystals from most of the reported peptide-related macrocycles, , our peptidomimetic macrocycles, 1L , 1D , and 3 , were found to easily crystallize such that a large quantity of blocky and needle crystals of 1L and 1D could be obtained in a high yield of 80% in the CH 3 OH–DMF mixed solvent in only 1 day (Figure S20). This provides an interesting type of polymeric porous materials of the HOF that has hitherto been reported mostly from rigid molecular building blocks. − These first examples of PM-HOFs may in the future find their applications as functional porous crystalline materials.…”

Constitutive Expression of Cyclotide kalata B1 Gene in Transgenic Rice Conferring Resistance to Golden Apple Snail (Pomacea canaliculata)

“…The focus of spectrum analysis is on the amide region, which spans from 7.0 to 9.0 ppm. This analysis is crucial because the hydrogen bonding patterns within proteins, as detected by NMR, rely on experiments involving deuterium exchange or temperature-induced shifts in amide proton chemical shifts (Handley et al 2020).…”