Cyclophilins: The Structure and Functions of an Important Peptidyl-prolyl Isomerase

Cyclophilins are a subgroup of highly conserved protein family immunophilins which are peptidyl-prolyl isomerases that interconvert between the cis and trans positions. They can act as chaperones in maintaining conformational quality control of proteomes. They are structurally conserved throughout evolution and have been found in mammals, plants, insects, fungi, and bacteria. They share a common fold architecture consisting of 8 antiparallel beta sheets and two alpha helices that pack against the sheets. They exist in the cellular compartment of most tissues and encode special functions. Intracellular Cyclophilins are secreted from cells in response to inflammatory stimuli and can mediate intercellular communication. Pro-inflammatory signals may be stimulated by extracellular Cyclophilin. Overexpression of Cyclophilins can contribute to pathological conditions. Cyclophilins are involved in the pathogenesis of viral infection, neurodegenerative diseases, ageing and cancer. Exhibiting several molecular functions, Cyclophilins can bind to cyclosporine and calcium-dependent ser/thr Calcineurin and has been used to describe the immunosuppressive action of cyclosporine. Cyclophilin can stabilize the cis-trans conformation transition state and speed up isomerization steps in protein folding. This process is important in the assembly of multiple domain proteins. Their existence as foldases and molecular chaperones enable them to be able to assist in the covalent folding or unfolding and the assembly or disassembly of other macromolecular structures.