The three-dimensional structure of a Plasmodium falciparum cyclophilin in complex with the potent anti-malarial cyclosporin A

Cyclosporin A (CsA) is a potent anti-malarial compound in vitro and in vivo in mice though better known for its immunosuppressive properties in humans . Crystal structures of wild-type and a double mutant Plasmodium falciparum cyclophilin (PfCyP19 and mPfCyP19) complexed with CsA have been determined using diffraction terms to a resolution of 2.1 Angstrom (1 Angstrom = 0.1 nm). The wild-type has a single PfCyP19/CsA complex per asymmetric unit in space group P1 and refined to an X-work of 0.15 and X-free of 0.19. An alte red cyclophilin, with two accidental mutations, Phe120 to Leu in the CsA bi nding pocket and Leu171 to Trp at the C terminus, presents two complexes pe r asymmetric unit in the orthorhombic space group P2(1)2(1)2. This refined to an X-work of 0.18 and X-free 0.21. The mutations were identified from th e crystallographic analysis and the C-terminal alteration helps to explain the different crystal forms obtained. PfCyP19 shares approximately 61% sequ ence identity with human cyclophilin A (hCyPA) and the structures are simil ar, consisting of an eight-stranded antiparallel beta-barrel core capped by two alpha-helices. The fold creates a hydrophobic active-site, the floor o f which is formed by side-chains of residues from four antiparallel beta-st rands and the walls from loops and turns. We identified C-H ... O hydrogen bonds between the drug and protein that may be an important feature of cycl ophilins and suggest a general mode of interaction between hydrophobic mole cules. Comparisons with cyclophilin-dipeptide complexes suggests that a spe cific C-H ... O hydrogen bonding interaction may contribute to ligand bindi ng. Residues Ser106, His99 and Asp130, located close to the active site and conserved in most cyclophilins, are arranged in a manner reminiscent of a serine protease catalytic triad. A Ser106Ala mutant was engineered to test the hypothesis that this triad contributes to CyP function. Mutant and wild -type enzymes were found to have similar catalytic properties. (C) 2000 Aca demic Press.