Cyclosporin A Cyclosporin exerts its effect by binding to the cytoplasmic cyclophilin, forming a complex that blocks the phosphatase activity of calcineurin. Cyclosporin A in single crystals or in chloroform solution adopt a distinct backbone conformation with a 9,10- cis peptide bond and three transannular hydrogen bonds. When bound to cyclophilin A, cyclosporin A adopts an extended conformation. There is no regular secondary structure or intramolecular hydrogen bonds.
Peptide bonds assume the trans configuration.
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