A functionally Pin1-like peptidyl-prolyl cis/trans isomerase (PPIase(1)) wa
s isolated from proembryogenic masses (PEMs) of Digitalis lanata according
to its enzymatic activity. Partial sequence analysis of the purified enzyme
(DlPar13) revealed sequence homology to members of the parvulin family of
PPIases. Similar to human Pin1 and yeast Ess1, it exhibits catalytic activi
ty toward substrates containing (Thr(P)/Ser(P))-Pro peptide bonds and compa
rable inhibition kinetics with juglone. Unlike Pin1-type enzymes it lacks t
he phosphoserine or phosphothreonine binding WW domain. Western blotting wi
th anti-DlPar13 serum recognized the endogenous form in nucleic and cytosol
ic fractions of the plant cells. Since the PIN1 homologue ESS1 is an essent
ial gene, complementation experiments in yeast were performed. When overexp
ressed in Saccharomyces cerevisiae DlPar13 is almost as effective as hPin1
in rescuing the temperature-sensitive phenotype caused by a mutation in ESS
1. 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 DlPar13 rather similar to parvulins of the Pin1-typ
e.