CypDs

CypDs, also known as cyclophilins, are a group of highly conserved, ubiquitously expressed proteins found in all domains of life. Their name derives from their ability to bind to the immunosuppressive drug cyclosporine A. CypDs are characterized by a conserved cyclophilin-type domain, which possesses peptidyl-prolyl cis-trans isomerase (PPIase) activity. This enzymatic activity allows them to catalyze the rate-limiting step of protein folding, specifically the isomerization of proline residues.

While their PPIase activity is a defining feature, research has revealed that CypDs play diverse roles beyond protein folding. They are involved in a multitude of cellular processes including transcription, translation, RNA processing, immune response, apoptosis, and viral replication. The specific functions of individual CypD members can vary depending on the organism and cellular context. They can act as chaperones, signaling molecules, or interact with various cellular partners to regulate their activity.

In humans, there are at least 15 identified CypD proteins, each with potentially distinct roles. Some CypDs are localized to specific cellular compartments like the cytoplasm, nucleus, mitochondria, or endoplasmic reticulum, which further influences their functions. Dysregulation or mutations in certain CypDs have been implicated in various diseases, including neurodegenerative disorders, viral infections, and cancer. Understanding the complex roles of CypDs is an active area of research with potential therapeutic implications.