title: Two structures of cyclophilin 40: folding and fidelity in the TPR domains.
abstract: BACKGROUND
  The "large immunophilin" family consists of domains of cyclophilin or FK506 binding protein linked to a tetratricopeptide (TPR) domain. They are intimately associated with steroid receptor complexes and bind to the C-terminal domain of Hsp90 via the TPR domain. The competitive binding of specific large immunophilins and other TPR-Hsp90 proteins provides a regulatory mechanism for Hsp90 chaperone activity.
  
  
  RESULTS
  We have solved the X-ray structures of monoclinic and tetragonal forms of Cyp40. In the monoclinic form, the TPR domain consists of seven helices of variable length incorporating three TPR motifs, which provide a convincing binding surface for the Hsp90 C-terminal MEEVD sequence. The C-terminal residues of Cyp40 protrude out beyond the body of the TPR domain to form a charged helix-the putative calmodulin binding site. However, in the tetragonal form, two of the TPR helices have straightened out to form one extended helix, providing a dramatically different conformation of the molecule.
  
  
  CONCLUSIONS
  The X-ray structures are consistent with the role of Cyclophilin 40 as a multifunctional signaling protein involved in a variety of protein-protein interactions. The intermolecular helix-helix interactions in the tetragonal form mimic the intramolecular interactions found in the fully folded monoclinic form. These conserved intra- and intermolecular TPR-TPR interactions are illustrative of a high-fidelity recognition mechanism. The two structures also open up the possibility that partially folded forms of TPR may be important in domain swapping and protein recognition.
authors.affiliation: Structural Biochemistry Group, Institute of Cell and Molecular Biology, The University of Edinburgh, Michael Swann Building, King's Buildings, Mayfield Road, EH9 3JR, Edinburgh, United Kingdom.
authors.forename: P
authors.initials: P
authors.lastname: Taylor
authors.forename: J
authors.initials: J
authors.lastname: Dornan
authors.forename: A
authors.initials: A
authors.lastname: Carrello
authors.forename: R F
authors.initials: RF
authors.lastname: Minchin
authors.forename: T
authors.initials: T
authors.lastname: Ratajczak
authors.forename: M D
authors.initials: MD
authors.lastname: Walkinshaw
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D002417:Cattle; D018360:Crystallography, X-Ray; D000081406:Peptidyl-Prolyl Isomerase F; D021983:Cyclophilins; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D019696:Peptidylprolyl Isomerase / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D002352:Carrier Proteins; D000081406:Peptidyl-Prolyl Isomerase F; D018841:HSP90 Heat-Shock Proteins; D010455:Peptides; D021983:Cyclophilins; D019696:Peptidylprolyl Isomerase