Conformational Heterogeneity of Cyclosporin A in Cyclophilin 18 Binding

Cyclosporin A: Conformational Complexity and Chameleonicity

The chameleonic behavior of cyclosporin A (CsA) was investigated through conformational ensembles employing multicanonical molecular dynamics simulations that could sample the cis and trans isomers of N-methylated amino acids; these assessments were conducted in explicit water, dimethyl sulfoxide, acetonitrile, methanol, chloroform, cyclohexane (CHX), and n-hexane (HEX) using AMBER ff03, AMBER10:EHT, AMBER12:EHT, and AMBER14:EHT force fields. The conformational details were discussed employing the free-energy landscapes (FELs) at T = 300 K; it was observed that the experimentally determined structures of CsA were only a part of the conformational space. Comparing the ROESY measurements in CHX-d12 and HEX-d14, the major conformations in those apolar solvents were essentially the same as that in CDCl₃ except for the observation of some sidechain rotamers. The effects of the metal ions on the conformations, including the cis/trans isomerization, were also investigated. Based on the analysis of FELs, it was concluded that the AMBER ff03 force field best described the experimentally derived conformations, indicating that CsA intrinsically formed membrane-permeable conformations and that the metal ions might be the key to the cis/trans isomerization of N-methylated amino acids before binding a partner protein.

Cyclosporin Structure and Permeability: From A to Z and Beyond

Cyclosporins are natural or synthetic undecapeptides with a wide range of actual and potential pharmaceutical applications. Several members of the cyclosporin compound family have remarkably high passive membrane permeabilities that are not well-described by simple structural metrics. Here we review experimental studies of cyclosporin structure and permeability, including cyclosporin-metal complexes. We also discuss models for the conformation-dependent permeability of cyclosporins and similar compounds. Finally, we identify current knowledge gaps in the literature and provide recommendations regarding future avenues of exploration.

Using 1H and 13C NMR chemical shifts to determine cyclic peptide conformations: a combined molecular dynamics and quantum mechanics approach

Conformational analysis from NMR and density-functional prediction of low-energy ensembles (CANDLE), a new approach for determining solution structures.

Synthesis and biochemical evaluation of two novel N-hydroxyalkylated cyclosporin A analogs

N-Hydroxyalkylation of cyclosporine A residues Val5 and d-Ala8 significantly influenced their conformation behavior and pharmacological properties.

Thioxylated cyclosporin A for studying protein-drug interactions

Single atom substitution of cyclosporin A (CsA) through thioxylation has been used to study the structure-activity relationship of the immunosuppressive complex, involving the CsA receptor protein cyclophilin 18 (Cyp18) and the immunological target protein phosphatase calcineurin (CaN), illustrating the contributions of peptide backbone in protein-drug interaction. Moreover, the subtle difference between thioxylation positions in CsA has led to a remarkable change in the quenching effect on Cyp18 intrinsic fluorescence. Using the thioxylated compound Cs7 as an isosteric derivative of CsA in competition assay, the experiment has led to the determination of k_off value in solution. Whereas the conformational heterogeneity of CsA has been found to be associated with its two-phase binding kinetics to Cyp18, the dissociation rate of CsA from complex is independent from the initial ligand structure.