Human T cell cyclophilin18 binds to thiol-specific antioxidant protein Aop1 and stimulates its activity.

Cyclophilins (CyPs) define a family of proteins binding to the immunosuppressive drug cyclosporin A (CsA). They are evolutionary highly conserved proteins being present in both pro- and eukaryotes and in different subcellular locations. CyPs possess enzymatic activity, namely peptidyl-prolyl cis-trans isomerase (PPIase) activity and are involved in cellular protein folding and protein interactions. Here we describe a novel interaction of human T cell cyclophilin18 (hCyP18). Abundant cytosolic hCyP18 binds to the thiol-specific antioxidant protein Aop1 and stimulates its enzymatic activity. Aop1 belongs to a family of proteins thought to be involved in defense of oxidative stress. The interaction of both proteins seem to be specific, since other PPIases do not have any stimulatory effect on Aop1.