Cyclophilin

Cyclophilin is a type of protein that has peptidyl-prolyl isomerase activity, which means it can catalyze the isomerization of peptide bonds from trans to cis form in the peptide chain. This activity is crucial for protein folding, which is a fundamental process in the cell. Cyclophilins are found in all types of organisms, from bacteria to humans.

Structure

Cyclophilins are characterized by their highly conserved sequence and three-dimensional structure. The core of the protein is an eight-stranded antiparallel beta-barrel, with two alpha helices packed against it. The active site of the enzyme is located in the hydrophobic core of the beta-barrel.

Function

The primary function of cyclophilins is to bind to the immunosuppressant drug cyclosporin A, which is used in organ transplantation to prevent rejection. The cyclophilin-cyclosporin A complex then binds to and inhibits the protein calcineurin, which is involved in the activation of T-cells, a type of white blood cell. This inhibition prevents the immune response and allows the transplanted organ to be accepted by the body.

Cyclophilins also have a role in the replication of viruses. For example, the human immunodeficiency virus (HIV) requires the presence of cyclophilin A in the host cell to replicate. Inhibitors of cyclophilin have been shown to have antiviral activity against HIV.

Clinical significance

Due to their role in immune response and viral replication, cyclophilins are a target for drug development. In addition to cyclosporin A, other cyclophilin inhibitors have been developed and are being tested for their potential use in treating diseases such as hepatitis C and HIV.

See also

• Immunophilin
• FKBP
• Pin1

• Cyclophilin A-cyclosporin complex
  Cyclophilin A-cyclosporin complex
• 
  Cyclophilin structure