Effect of different immunosuppressive drugs on calcineurin and its mutants

Several mutants in Loop7 region and near Loop7 region of calcineurin A (CN A) subunit have been constructed and purified using site-directed mutagenes is. Their phosphatase activity and the corresponding solution conformation were examined. Their phosphatase activities between wild-type CN and mutant s were compared to identify the interaction of different immunosuppressive drugs with CN. The results showed that the phosphatase activities of the mu tants at Loop7 were much higher than the one of wild-type CN. Furthermore, circular dichroism spectra of the mutants revealed that their solution conf ormations gave rise in changes in native structure of the protein. Cyclophi lin-CyclosporinA (CyP-CsA) significantly inhibited the phosphatase activity of wild-type CN, and had no effects on the phosphatase activity of mutants in Loop7 region, which indicates that the site-directed mutagenesis at Loo p7 region made a significant change in the interaction between CyP-CsA and CN. Examination of the activities of these mutants resulted in the presence of immunosuppressive component from traditional Chinese drugs. The compone nt of Chinese drug, ZIP1, could directly inhibit both CN and CN mutants wit hout drug binding protein. These results suggest that the Loop7 region is a n important structural area involved in the inhibition by CyP-CsA. It is va luable to further study the inhibition by ZIP1.