Type 2C protein phosphatases in fungi

Abstract

Type 2C Ser/Thr phosphatases are a remarkable class of protein phosphatases, which are conserved in eukaryotes and involved in a large variety of functional processes. Unlike in other Ser/Thr phosphatases, the catalytic polypeptide is not usually associated with regulatory subunits, and functional specificity is achieved by encoding multiple isoforms. For fungi, most information comes from the study of type 2C protein phosphatase (PP2C) enzymes in Saccharomyces cerevisiae, where seven PP2C-encoding genes (PTC1 to -7) with diverse functions can be found. More recently, data on several Candida albicans PP2C proteins became available, suggesting that some of them can be involved in virulence. In this work we review the available literature on fungal PP2Cs and explore sequence databases to provide a comprehensive overview of these enzymes in fungi.

Fig. 1.

The type 2C protein phosphatase family members in Saccharomyces cerevisiae. A schematic representation of the primary structures of the seven PP2C isoforms is shown. The black lines represent each protein, and the blue boxes indicate the catalytic domain of each phosphatase (PP2C domain, SM00332, according to the SMART database [82]). The numbers included within the catalytic domain indicate the amino acid residues spanning these domains. The number at the C terminus indicates the number of amino acids of the protein. “ORF” refers to the systematic name of the gene. Alternative denominations (aliases) and subcellular localization are indicated (Cyt, cytoplasm; Nuc, nucleus; Mit, mitochondria). Alternative splicing of YHR076W can generate two proteins, Ptc7u (unspliced) and Ptc7s (spliced), with different cellular functions (45). The orange box denotes the transmembrane domain extending from residue 17 to 39 of the Ptc7u protein. Percentages of similarity and identity of overlapping regions of different PP2Cs in comparison to Ptc1 are shown (determined by FASTA using the BLOSUM50 matrix). The dendrogram on the right was generated using the entire protein sequences and the ClustalW algorithm using the default settings (Kyoto University Bioinformatic Center).

Fig. 2.

Functional role of PP2C enzymes in yeast MAPK pathway regulation and organelle inheritance. (a) Regulation of MAPK pathways. Different S. cerevisiae and S. pombe pathways are depicted, indicating the triggering stimuli and the transcription factors involved in the response. The three layers defining the MAPK pathways are shaded in gray. Discontinuous lines denote suspected or still poorly characterized interactions. See text for details. (b) The central role of Ptc1 and the different proteins presumed to mediate the phosphatase function on organelle inheritance. Note that only endoplasmic reticulum and mitochondrial inheritances seem to require Slt2 MAPK intervention.

Fig. 3.

The diversity of PP2Cs in fungi. The NCBI protein database was searched for PP2C-related proteins using the BLAST algorithm and the seven PP2C sequences from S. cerevisiae. Hits were manually curated, and 144 protein sequences were selected. (a) A ClustalW2 alignment was performed, and the results are displayed as a radial tree using the TreeView software. Branches were manually labeled. Ptc6-R, Ptc6-related family; Ptc7-R, Ptc7-related family. (b) Fungal phylogeny is represented as a tree based on data from reference , with some modifications. The presence (numbers) or absence (gray boxes) of the indicated PP2C proteins in each organism is represented. The numeric code is described in the legend to Fig. S1 in the supplemental material, where the accession numbers for each sequence can be found.