Functional Conservation of Phosphorylation-specific Prolyl Isomerases in Plants

Abstract

The phosphorylation-specific peptidyl prolyl cis/trans isomerase (PPIase) Pin1 in humans and its homologues in yeast and animal species play an important role in cell cycle regulation. These PPIases consist of an NH 2 -terminal WW domain that binds to specific phosphoserine-or phosphothreonine-proline motifs present in a subset of phosphoproteins and a COOH-terminal PPIase domain that specifically isomerizes the phosphorylated serine/threonine-proline peptide bonds. Here, we describe the isolation of MdPin1, a Pin1 homologue from the plant species apple (Malus domestica) and show that it has the same phosphorylation-specific substrate specificity and can be inhibited by juglone in vitro, as is the case for Pin1. A search in the plant expressed sequence tag data bases reveals that the Pin1-type PPIases are present in various plants, and there are multiple genes in one organism, such as soybean (Glycine max) and tomato (Lycopersicon esculentum). Furthermore, all these plant Pin1-type PPIases, including AtPin1 in Arabidopsis thaliana, do not have a WW domain, but all contain a four-amino acid insertion next to the phosphospecific recognition site of the active site. Interestingly, like Pin1, both MdPin1 and AtPin1 are able to rescue the lethal mitotic phenotype of a temperature-sensitive mutation in the Pin1 homologue ESS1/PTF1 gene in Saccharomyces cerevisiae. However, deleting the extra four amino acid residues abolished the ability of AtPin1 to rescue the yeast mutation under non-overexpression conditions, indicating that these extra amino acids may be important for mediating the substrate interaction of plant enzymes. Finally, expression of MdPin1 is tightly associated with cell division both during apple fruit development in vivo and during cell cultures in vitro. These results have demonstrated that phosphorylationspecific PPIases are highly conserved functionally in yeast, animal, and plant species. Furthermore, the experiments suggest that although plant Pin1-type enzymes do not have a WW domain, they may fulfill the same functions as Pin1 and its homologues do in other organisms.

Regulation of Arabidopsis SHY2/IAA3 protein turnover

“…It covalently attaches to sulfhydryl groups of cysteine residues in target proteins (Hennig et al, 1998). One known target of juglone is the parvulin class of peptidyl prolyl isomerases (Hennig et al, 1998;Metzner et al, 2001;Yao et al, 2001), and our results therefore raise the possibility that these enzymes might regulate SHY2/IAA3 protein turnover. This is an attractive hypothesis because two adjacent proline residues in conserved domain II (one of which is mutated in shy2-2) are important for the instability of Aux/ IAA proteins (Ramos et al, 2001).…”

“…This is an attractive hypothesis because two adjacent proline residues in conserved domain II (one of which is mutated in shy2-2) are important for the instability of Aux/ IAA proteins (Ramos et al, 2001). One caveat to this model is that animal and plant parvulins act on phosphorylated substrates (at least for the peptide substrates tested) (Landrieu et al, 2000;Metzner et al, 2001;Yao et al, 2001), whereas we have found no evidence for a phosphorylation requirement for SHY2/IAA3 recognition of TIR1:: myc, and furthermore domain II lacks an obvious phosphorylation site (Ramos et al, 2001). Juglone probably has additional targets that have not been identi®ed (Chao et al, 2001).…”

Immunophilins and Parvulins. Superfamily of Peptidyl Prolyl Isomerases in Arabidopsis

“…Unlike its homologs, the plant PIN1 like protein does not have the conserved WW-domain that is believed to be required for the recognition of phosphoprotein substrates (Lu et al, 1999). However, it still retains the phospho-substrate specificity and can complement yeast mutant lacking ESS1 (Landrieu et al, 2000;Metzner et al, 2001;Yao et al, 2001). The activity of the other human parvulin, hPar14, is independent from substrate phosphorylation (Rulten et al, 1999;Uchida et al, 1999).…”

Prolyl isomerase Pin1: a catalyst for oncogenesis and a potential therapeutic target in cancer

“…Pin1 homologues are highly conserved in eukaryotes (Huang et al, 2001;Landrieu et al, 2000;Metzner et al, 2001;Yao et al, 2001;Zhou et al, 1999), and the budding yeast homologue, Ess1p/Ptrf1p, was isolated a long time ago but did not have any previously known activity (Hanes et al, 1989;Hani et al, 1995). With the exception of the plant enzymes, which appear to contain only PPIase domains, most other Pin1-type PPIases also contain an N-terminal WW domain.…”