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 immunos uppressive drug cyclosporin A (CsA). They are evolutionary highly cons erved proteins being present in both pro- and eukaryotes and in differ ent subcellular locations. CyPs possess enzymatic activity, namely pep tidyl-prolyl cis-trans isomerase (PPIase) activity and are involved in cellular protein folding and protein interactions. Hero we describe a novel interaction of human T cell cyclophilin18 (hCyP18). Abundant cy tosolic hCyP18 binds to the thiol-specific antioxidant protein Aop1 an d stimulates its enzymatic activity. Aop1 belongs to a family of prote ins thought to be involved in defense of oxidative stress. The interac tion of both proteins seem to be specific, since other PPIases do not have any stimulatory effect on Aop1. (C) 1998 Academic Press Limited.