A complementary DNA (cDNA) for human cyclophilin C (Cyp-C) was isolated from a human kidney cDNA library. Northern blot experiments with several human tissues and cell lines revealed that Cyp-C is less abundant than Cyp-A. The amount of Cyp-C mRNA was 10-fold lower than that of Cyp-A in kidney. Expression of human Cyp-C in the kidney is not significantly elevated compared to pancreas, skeletal muscle, heart, lung, and liver. This argues against a previously postulated specific role for Cyp-C in the nephrotoxic effects of CsA in humans, based on the studies of its relative abundance in murine kidney. It is present in extremely low concentrations in brain and in the Jurkat T cell line. The binding of recombinant human Cyp-A, -B, and -C to cyclosporin A (CsA) was studied by immunochemical methods. The relative affinity of Cyp-C for CsA is lower by a factor of 2 than that of Cyp-A, which itself is 10-fold lower than that of Cyp-B. Cross-reactivity studies with a series of Cs derivatives showed that Cyp-C binds CsA with a fine specificity similar to that of Cyp-A and Cyp-B. Cs amino acid residues 1, 2, 10, and 11 seemed essential for the interaction with all three Cyp subtypes. However, Cyp-C tolerates a greater variety of structures on Cs at position 2 than Cyp-A does, suggesting that this residue of CsA might not be in tight contact with Cyp-C. This was confirmed by modeling of human Cyp-C on the structure of the complex formed by Cyp-A and CsA. The knowledge of the fine specificity of human Cyps for CsA and of their expression levels may provide better insights into how CsA acts on its different target proteins in vivo.

The pepM gene coding for a methionine-specific aminopeptidase was cloned from Salmonella typhimurium and its nucleotide sequence determined. The gene encoded a 264 amino acid protein that was homologous to a similar protein from Escherichia coli. The sequence of an overproducer mutant allele, pepM100, contained a single base change in the likely--35 region of the pepM promoter that increased its homology to the consensus promoter sequence. A region downstream from the pepM coding sequence contained extensive inverted repeats and was homologous to sequences found elsewhere in both Salmonella and other bacterial species.