Functional Replacement of the Essential ESS1 in Yeast by the Plant Parvulin DlPar13

A functionally Pin1-like peptidyl-prolyl cis/trans isomerase (PPIase 1 ) was isolated from proembryogenic masses (PEMs) of Digitalis lanata according to its enzymatic activity. Partial sequence analysis of the purified enzyme ( Dl Par13) revealed sequence homology to members of the parvulin family of PPIases. Similar to human Pin1 and yeast Ess1, it exhibits catalytic activity toward substrates containing (Thr(P)/Ser(P))-Pro peptide bonds and comparable inhibition kinetics with juglone. Unlike Pin1-type enzymes it lacks the phosphoserine or phosphothreonine binding WW domain. Western blotting with anti- Dl Par13 serum recognized the endogenous form in nucleic and cytosolic fractions of the plant cells. Since the PIN1 homologue ESS1 is an essential gene, complementation experiments in yeast were performed. When overexpressed in Saccharomyces cerevisiae Dl Par13 is almost as effective as hPin1 in rescuing the temperature-sensitive phenotype caused by a mutation in ESS1 . In contrast, the human parvulin hPar14 is not able to rescue the lethal phenotype of this yeast strain at nonpermissive temperatures. These results suggest a function for Dl Par13 rather similar to parvulins of the Pin1-type.