A Conformation of Cyclosporin A in Aqueous Environment Revealed by the X-Ray Structure of a Cyclosporin-Fab Complex

Abstract

The conformation of the immunosuppressive drug cyclosporin A (CsA) in a complex with a Fab molecule has been established by crystallographic analysis to 2.65 angstrom resolution. This conformation of CsA is similar to that recently observed in the complex with the rotamase cyclophilin, its binding protein in vivo, and totally different from its conformation in an isolated form as determined from x-ray and nuclear magnetic resonance analysis. Because the surfaces of CsA interacting with cyclophilin or with the Fab are not identical, these results suggest that the conformation of CsA observed in the bound form preexists in aqueous solution and is not produced by interaction with the proteins.

Interaction of cyclosporin A with an Fab fragment or cyclophilin Affinity measurements and time‐dependent changes in binding

“…The antibody to CS used in the present study is antibody V45-271-11 [12]. This antibody differs from antibody R45-45-11 used for crystallographic analysis of an Fab-CS complex [1] by a single amino acid change of Phe to Tyr at position 58 (Kabat numbering, [13]) located in the H2 loop [14]. Crystallographic analysis shows that this amino acid does not contact CS [15].…”

“…Recently the structures of two complexes of CS with a protein have been published. The complex between CS and the Fab fragment of a monoclonal antibody has been solved by crystallographic analysis to 2.65 /k resolution [1]. The structure of CS complexed to cyclophilin (CYP), its binding protein in vivo, has also been obtained both by X-ray crystallography [2] and nuclear magnetic resonance [3,4].…”

The 3D structure of a cyclosporin analogue in water is nearly identical to the cyclophilin‐bound cyclosporin conformation

“…Kinetic and spectroscopic studies [17] with the aid of all-trans amide or 9,10-cis amide conformations [ 18,191 of CS showed evidence of a time and solvent dependent inhibition of the peptidyl-prolyl cisltruns isomerase activity of CYP by CS and allowed the hypothesis that CYP could bind a conformation of CS already present in water [20], rather than inducing a new conformation. …”

Oral cyclosporine A - the current picture of its liposomal and other delivery systems

“…The dominant conformation in an apolar solvent, the basic features of which are the presence of intramolecular H-bonds stabilizing the structure of a twisted β-sheet and a type II β-turn at amino acid residues 3 and 4, changes dramatically in polar solvents where the molecule exposes its H-bonding groups and loses its secondary structure (Fig. 1) [24][25][26]. The CsA molecule forms a rigid complex with its receptor, cyclophilin, with half of its residues (Sar3-Dal8) exposed to the solvent and the other residues (Bmt1, Aba2, Mle9-Mva11) buried in the receptor molecule [27].…”

“…The chemical structure of cyclosporine A. A -The conformation of CsA in an aqueous environment revealed by the X-ray structure of a CsA-FAB complex (PDB ID: 1IKF) [25]. The abbreviations of the CsA residues are: Bmt, (4R)-4[(E)-2 butenyl]-4,Ndimethyl-L-threonine; Aba, L-a-aminobutyric acid; Sar, sarcosine; Mle, N-methyl leucine; Dal, D-alanine; Mva, N-methyl valine.…”