Three-dimensional solution structure of Escherichia coli periplasmic cyclophilin

The solution structure of the periplasmic cyclophilin type cis-trans peptidyl-prolyl isomerase from Escherichia coli (167 residues, MW > 18.200) has been determined using multidimensional heteronuclear NMR spectroscopy and distance geometry calculations. The structure determination is based on a total of 1720 NMR-derived restraints (1566 distance and 101 phi and 53 chi 1 torsion angle restraints). Twelve distance geometry structures were calculated, and the average root-mean-square (rms) deviation about the mean backbone coordinate positions is 0.84 +/- 0.18 A for the backbone atoms of residues 5-165 of the ensemble. The three-dimensional structure of E. coli cyclophilin consists of an eight-stranded antiparallel beta-sheet barrel capped by alpha-helices. The average coordinates of the backbone atoms of the core residues of E. coli cyclophilin have an rms deviation of 1.44 A, with conserved regions in the crystal structure of unligated human T cell cyclophilin [Ke, H. (1992) J. Mol. Biol. 228, 539-550]. Four regions proximal to the active site differ substantially and may determine protein substrate specificity, sensitivity to cyclosporin A, and the composite drug:protein surface required to inhibit calcineurin. A residue essential for isomerase activity in human T cell cyclophilin (His126) is replaced by Tyr122 in E. coli cyclophilin without affecting enzymatic activity.