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Ribbon diagram of cyclophilin A in complex with ciclosporin (yellow). From PDB 1CWA.
peptidylprolyl isomerase A (cyclophilin A)
Symbol PPIA
Entrez 5478
HUGO 9253
OMIM 123840
RefSeq NM_203430
UniProt Q3KQW3
Other data
EC number
Locus Chr. 7 p13
peptidylprolyl isomerase D (cyclophilin D)
Symbol PPID
Entrez 5481
HUGO 9257
OMIM 601753
RefSeq NM_005038
UniProt Q08752
Other data
Locus Chr. 4 q31.3

Cyclophilins, abbreviated CyP (not to be confused with CYP, which is the approved abbreviation for cytochrome P450), are proteins that bind to ciclosporin (cyclosporine A), an immunosuppressant which is usually used to suppress rejection after internal organ transplants. These proteins have peptidyl prolyl isomerase activity, which catalyzes the isomerization of peptide bonds from trans form to cis form at proline residues and facilitates protein folding.

Cyclophilin A

Human peptidylprolyl isomerase A, which exists in cytosol, has a beta barrel structure with two alpha helices and a beta-sheet. Other cyclophilins have similar structures to cyclophilin A. The cyclosporin A-cyclophilin A complex inhibits a calcium/calmodulin-dependent phosphatase, calcineurin, the inhibition of which is thought to suppress organ rejection.

Cyclophilin D

Cyclophilin D, which is located in the matrix of mitochondria, is a component of the mitochondrial permeability transition pore. The pore opening raises the permeability of the mitochondrial inner membrane, allows influx of cytosolic molecules into the mitochondrial matrix, increases the matrix volume, and disrupts the mitochondrial outer membrane. As a result, the mitochondria fall into a functional disorder, so the opening of the pore plays an important role in cell death. Cyclophilin D is thought to regulate the opening of the pore because cyclosporin A, which binds to CyP-D, inhibits the pore opening.

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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Cyclophilin". A list of authors is available in Wikipedia.
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