3-DIMENSIONAL SOLUTION STRUCTURE OF ESCHERICHIA-COLI PERIPLASMIC CYCLOPHILIN

The solution structure of the periplasmic cyclophilin type cis-trans p eptidyl-prolyl isomerase from Escherichia coil (167 residues, MW > 18. 200) has been determined using multidimensional heteronuclear NMR spec troscopy and distance geometry calculations. The structure determinati on is based on a total of 1720 NMR-derived restraints (1566 distance a nd 101 phi and 53 chi(1) torsion angle restraints). Twelve distance ge ometry structures were calculated, and the average root-mean-square (r ms) deviation about the mean backbone coordinate positions is 0.84 +/- 0.18 Angstrom for the backbone atoms of residues 5-165 of the ensembl e. The three-dimensional structure of E. coli cyclophilin consists of an eight-stranded antiparallel beta-sheet barrel capped by alpha-helic es. The average coordinates of the backbone atoms of the core residues of E. coli cyclophilin have an rms deviation of 1.44 Angstrom, with c onserved regions in the crystal structure of unligated human T cell cy clophilin [Ke, H. (1992) J. Mol. Biol. 228, 539-550]. Four regions pro ximal to the active site differ substantially and may determine protei n substrate specificity, sensitivity to cyclosporin A, and the composi te drug:protein surface required to inhibit calcineurin. A residue ess ential for isomerase activity in human T cell cyclophilin (His126) is replaced by Tyr 122 in E. coli cyclophilin without affecting enzymatic activity.