PPIL3 Human

Cyclophilin-J (CYPJ) is a member of the cyclophilin family of peptidyl-prolyl cis/trans-isomerases (PPIases). These enzymes catalyze the isomerization of peptide bonds at proline residues, which is crucial for protein folding and function. Cyclophilins are highly conserved and found in a wide range of organisms, from bacteria to humans .

Cyclophilin-J is structurally similar to other members of the cyclophilin family, particularly Cyclophilin A (CYPA), with which it shares approximately 50% sequence identity . Recombinant human Cyclophilin-J (hCYPJ) has been expressed in Escherichia coli and purified for biochemical studies .

The catalytic efficiency of CYPJ, measured as the catalytic number/Michaelis constant (kcat/KM), is 9.5×10^4 s–1M–1 . CYPJ can catalyze the isomerization of norleucine-proline, isoleucine-proline, and glutamine-proline peptides, which are substrates not typically catalyzed by CYPA and Escherichia coli PPIases .

Cyclophilin-J is sensitive to inhibition by the immunosuppressive drug cyclosporin A (CsA). The half-maximal inhibitory concentration (IC50) of CsA for CYPJ is 12.1±0.9 μM . CsA forms a complex with cyclophilins, which interrupts the T-cell signaling pathway, leading to immunosuppression .

Cyclophilins, including CYPJ, are involved in various biological processes such as immunosuppression, signal transduction, protein folding, and apoptosis . CYPJ has been shown to significantly up-regulate the transcription of several genes involved in cell growth, proliferation, and apoptosis, including E-box, E2F, retinoblastoma (Rb), p53, activator protein 1 (AP1), NF-ĸB, and phospho-cAMP response element (CRE) cis-response elements in 293T cells .