FK 506-binding protein proline rotamase is a target for the immunosuppressive agent FK 506 in Saccharomyces cerevisiae.

FK 506 and cyclosporin A are potent immunosuppressive compounds that inhibit T-cell activation by interfering with signal transduction. In vitro, FK 506 binds and inhibits the activity of FK 506-binding protein (FKBP), a peptidylprolyl rotamase (cis-trans isomerase). Cyclosporin A acts similarly on a different proline rotamase, cyclophilin. Experiments described here demonstrate genetically that FKBP is a target for FK 506 in vivo. We have isolated the gene encoding the FKBP proline rotamase (FPR1) from Saccharomyces cerevisiae. The encoded yeast protein is highly homologous with bovine and human FKBP and shares no homology with cyclophilin. Disruption of FPR1 and CPR1 (encoding cyclophilin) individually or in combination is not lethal; thus, either enzymatic proline rotamerization is not essential for life or an unknown proline rotamase can substitute for the missing enzymes. Overexpression or disruption of FPR1 confers resistance to growth inhibition by FK 506, suggesting that FKBP is a target for FK 506 in yeast. However, FKBP is only one of at least two targets because strains lacking FKBP are only partially resistant to FK 506.