Cyclophilin 40 (CYP-40)

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, which binds to CyP-D, inhibits the pore opening.

Cyclophilin-40 (CyP40, also CYPD) was identified by Kieffer et al. (1992) as a 40-kD cyclophilin-like protein with PPIase activity. In the bovine uterus, CyP40 is a component of the estrogen receptor complex.