title: X-ray structure of a decameric cyclophilin-cyclosporin crystal complex.
abstract: Human cyclophilin A (CypA), a ubiquitous intracellular protein of 165 amino acids, is the major receptor for the cyclic undecapeptide immunosuppressant drug cyclosporin A (CsA), which prevents allograft rejection after transplant surgery and is efficacious in the field of autoimmune diseases. CsA prevents T-cell proliferation by blocking the calcium-activated pathway leading to interleukin-2 transcription. Besides their ability to bind CsA, the cyclophilin isoforms also have peptidyl-prolyl isomerase activity and enhance the rate of protein folding. The macrolide FK506 acts similarly to CsA and its cognate receptor FKBP also has peptidyl-prolyl isomerase activity. Inhibition of this enzymatic activity alone is not sufficient to achieve immunosuppression. A direct molecular interaction between the drug-immunophilin complex (CsA-CypA, or FK506-FKBP) and the phosphatase calcineurin, is responsible for modulating the T-cell receptor signal transduction pathway. Here we describe the crystal structure of a decameric CypA-CsA complex. The crystallographic asymmetric unit is composed of a pentamer of 1:1 cyclophilin-cyclosporin complexes of rather exact non-crystallographic fivefold symmetry. The 2.8 A electron density map is of high quality. The five independent cyclosporin molecules are clearly identifiable, providing an unambiguous picture of the detailed interactions between a peptide drug and its receptor. It broadly confirms the results of previous NMR, X-ray and modelling studies, but provides further important structural details which will be of use in the design of drugs that are analogues of CsA.
authors.affiliation: Biocentre, University of Basel, Switzerland.
authors.forename: G
authors.initials: G
authors.lastname: Pflügl
authors.forename: J
authors.initials: J
authors.lastname: Kallen
authors.forename: T
authors.initials: T
authors.lastname: Schirmer
authors.forename: J N
authors.initials: JN
authors.lastname: Jansonius
authors.forename: M G
authors.initials: MG
authors.lastname: Zurini
authors.forename: M D
authors.initials: MD
authors.lastname: Walkinshaw
mesh_terms: D000591:Amino Acid Isomerases / Q000737:chemistry*; D002352:Carrier Proteins / Q000737:chemistry*; D003461:Crystallography; D016572:Cyclosporine / Q000737:chemistry*; D006860:Hydrogen Bonding; D019696:Peptidylprolyl Isomerase; D013237:Stereoisomerism
chemical_list: D002352:Carrier Proteins; D016572:Cyclosporine; D000591:Amino Acid Isomerases; D019696:Peptidylprolyl Isomerase