Peptidyl-prolyl cis-trans isomerase from Bacillus subtilis. A prokaryotic enzyme that is highly sensitive to cyclosporin A.

Cyclophylins are members of a class of proteins with peptidyl-prolyl cis-trans isomerase activity. These enzymes bind the immunosuppressive agent, cyclosporin A (CsA), which acts as a competitive inhibitor. The peptidyl-prolyl cis-trans isomerase from Bacillus subtilis (PPIase) was purified to homogeneity in a 4-step purification procedure, which resulted in a 100-fold protein purification with a yield of 5%. Coomassie blue-stained SDS-PAGE revealed a single band of about 18 kDa. PPIase activity was determined using synthetic peptides as substrates in a 2-step reaction coupled to chymotrypsin. Treatment of Bacillus subtilis PPIase by CsA revealed an inhibition constant of Ki = 175 nM, which differs from cyclophilin of enterobacteria such as E. coli or Salmonella typhimurium and is in the range of human enzymes.