1 The Research Institute for Children, Children's Hospital, and Departments of Pediatrics, and Microbiology, Immunology, and Parasitology, Louisiana State University Health Sciences Center, New Orleans, LA 70118, USA
2 Departments of Molecular Genetics and Microbiology, Medicine, and Pharmacology and Cancer Biology and the Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710, USA
Genome Biology 2005, 6:226 doi:10.1186/gb-2005-6-7-226Published: 27 June 2005
Cyclophilins (Enzyme Commission (EC) number 18.104.22.168) belong to a group of proteins that have peptidyl-prolyl cis-trans isomerase activity; such proteins are collectively known as immunophilins and also include the FK-506-binding proteins and the parvulins. Cyclophilins are found in all cells of all organisms studied, in both prokaryotes and eukaryotes; humans have a total of 16 cyclophilin proteins, Arabidopsis up to 29 and Saccharomyces 8. The first member of the cyclophilins to be identified in mammals, cyclophilin A, is the major cellular target for, and thus mediates the actions of, the immunosuppressive drug cyclosporin A. Cyclophilin A forms a ternary complex with cyclosporin A and the calcium-calmodulin-activated serine/threonine-specific protein phosphatase calcineurin; formation of this complex prevents calcineurin from regulating cytokine gene transcription. Recent studies have implicated a diverse array of additional cellular functions for cyclophilins, including roles as chaperones and in cell signaling.