Abstract
Cyclophilins constitute a class of peptidyl-prolyl isomerases which participate in processes related to protein folding, signalling and chaperoning. The crystal structure of the cytoplasmic cyclophilin A (CyPA) from the bacterium Azotobacter vinelandii complexed with a synthetic tetrapeptide was determined by molecular replacement at 2 resolution. The proline in the tetrapeptide is observed to adopt the cis-isomer conformation. Comparisons of this structure with other CyPA structures provide insights into the conformational variability, effects of peptide binding and structure-function relationships of this enzyme.