SPECIFIC INTERACTION BETWEEN BOVINE CYCLOPHILIN-A AND SYNTHETIC ANALOGS OF CYCLOLINOPEPTIDE-A

Like cyclosporin A, cyclolinopeptide A binds specifically bovine cyclo philin A, inhibiting its peptidyl-prolyl cis-trans isomerase activity. We describe here the protein interaction with several synthetic analo gues of cyclolinopeptide A, which are either homodetic or disulphide b ridged heterodetic cyclopeptides characterized by different ring dimen sions, in terms of dissociation and inhibition constants evaluated by fluorescence and inhibition of the enzyme activity, respectively. Diss ociation constants from fluorescence experiments are practically ident ical and about 20-fold lower than for cyclosporin A. On the other hand , inhibition constants differ from compound to compound and are higher than for cyclosporin A. This result is therefore difficult to rationa lize, but we would suggest decoupling between binding and inhibitory a bility of cyclopeptides. The Pro(1) residue of cyclolinopeptide A seem s to play a fundamental role in determining the inhibition of the rota mase activity of cyclophilin A, as the homodetic analogue lacking this residue does not show any inhibitory ability, Similarly, heterodetic analogues with a ring size smaller than 7 residues do not display inhi bition. We presume that the sequence -Pro-Pro-Phe-Phe- and a ring size of 8 residues for homodetic cyclic peptides could be used as starting points in the targeted synthesis of cyclopeptides able to bind both c yclosporin A and calcineurin. The only peptide showing similar values of the dissociation and inhibition constant is cyclolinopeptide A. Thi s compound can be considered a novel model for the molecular design of immunosuppressant drugs.