Immunophilin

In molecular biology, immunophilins are endogenous cytosolic peptidyl-prolyl isomerases that interconvert [sic] between the cis and trans positions. They are chaperon molecules with peptidylprolyl isomerase activity that exists in two families, with different characteristics. These two families are "cyclosporin-binding cyclophilins (CyPs)" and "FK506-binding proteins (FKBPs)". However, there are also large molecules that contain both families on its opposite sides.

Immunophilins are the receptor molecules for the Immunosuppressive drugs. Immunophilins are targeted by immunosuppressive drugs such as sirolimus, cyclosporin, and tacrolimus. For these drugs in particular, known immunophilins such as cyclophilin catalyze the cis-trans isomerization of peptide bonds, particularly X-Pro peptide bonds. This prolyl isomerase activity can be inhibited by immunosuppressive drugs. Immunophilin complexes bind to calceneurin which inhibits the phosphate activity and engenders immunosuppresive effects. Immunophilins forms protein complex with ryanodine and inositol triphosphate (IP3) which impacts the release of calcium.

Cyclosoporin A(CsA), rapamycin and FK506 act as inhibitors for immunophilin receptor proteins. The family of CsA has eleven members. CsA and FK506 affect the calcium dependent step of T cell response which prevents release of interleukin-2.

FK506 binds with high affinity to other smaller proteins, such as FKBP-12. FKBP-12 and cyclophilins both share in common peptide-prolyl isomerase activity. Peptide bonds within proteins can exist in both a cis and trans isomer(s) form because of the double-bond characteristics within the molecule(s).

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