A novel type 2C protein phosphatase from the human fungal pathogen Candida albicans

Abstract

The reversible phosphorylation of proteins, controlled by protein kinases and protein phosphatases, is a critical mechanism by which eukaryotic organisms regulate cellular signal transduction pathways. There are two superfamilies of protein serine/threonine speci¢c phosphatases, the PPP and PPM families, which speci¢cally dephosphorylate serine/threonine residues [1]. The PPP family is comprised of three subtypes of phosphatases, PP1, PP2A and PP2B, which are distinguished by their associated regulatory subunits to form a variety of holoenzymes. These enzymes show considerable evolutionary sequence conservation in their catalytic domains, and the dephosphorylation activity of the PPP family is independent of divalent cations and can be inhibited by the protein inhibitors-1 and -2 as well as the tumor promoter okadaic acid. In contrast, PPM family members are monomeric enzymes and are unrelated in sequence to the PPP family, and they include type 2C protein phosphatases (PP2C) and the pyruvate dehydrogenase phosphate. Sequence analysis reveals that there are 11 conserved motifs in the members of the PP2C superfamily [2]. In addition, the dephosphorylation activity of PP2C requires metal cations, Mn 2 or Mg 2 , but its activity is not sensitive to the tumor promoter okadaic acid and other inhibitors of the PPP family [1]. In the budding yeast Saccharomyces cerevisiae, six PP2C-like genes, Ptc1p, Ptc2p, Ptc3p, Ptc4, Ptc5 and YCR079w, have been identi¢ed, and proteins encoded by the former ¢ve genes have been demonstrated to be PP2C enzymes [3]. In Candida albicans, an important human yeast pathogen, little is known about PP2C enzymes. In this report, we have identi¢ed and characterized the ¢rst PP2C phosphatase (CaPTC7) from the human fungal pathogen, C. albicans, representing a novel member of the PP2C superfamily.To investigate the roles of PP2C phosphatases in the pathogenesis of C. albicans, potential PP2C homologous sequences from the C. albicans genomic database (http://www-sequence.stanford.edu/group/candida) were extensively searched with the six known budding yeast PP2C-like genes as queries. As a result, the six C. albicans homologs of the known budding yeast PP2C-like genes were identi¢ed according to their sequence similarities (Jiang et al

Functional and Structural Characterization of RsbU, a Stress Signaling Protein Phosphatase 2C

“…This model is not without precedent in the PP2C phosphatase family; the catalytic subunit of bovine mitochondrial pyruvate dehydrogenase phosphatase displays a K m for magnesium that increases in the presence of its regulatory subunit (47). However, the K m value for Mn 2ϩ of RsbU, of RsbU in the presence of RsbT, and of the C-terminal domain of RsbU alone were found to be 0.96 mM in all three cases (data not shown) and thus similar to that observed for other PP2C phosphatases (48,49). It would therefore seem unlikely that RsbU is regulated by changes in the K m for its requisite co-factor.…”

Type 2C Protein Phosphatases in Fungi

“…Jiang and coworkers (41) demonstrated that CaPtc7 has the biochemical characteristics of classical PP2C enzymes (i.e., Mn 2ϩ -and Mg 2ϩ -dependent in vitro phosphatase activity blocked by NaF but not sensitive to okadaic acid). The Nterminal region of CaPtc7 contains a transmembrane domain and a potential mitochondrion-targeting signal that justifies its presence in this organelle (41,107). Homologues of CaPtc7 can be found in S. cerevisiae (Fig.…”

Identification of the Putative Protein Phosphatase GenePTC1as a Virulence-Related Gene Using a Silkworm Model ofCandida albicansInfection

“…Furthermore, a deletion mutant of cnb1, which encodes a regulatory subunit of calcineurin, has significantly attenuated virulence in a mouse model of C. albicans infection (6). Other C. albicans genes identified as protein phosphatases include CDC14 (13), CYR1 (24,36), CPP1 (14), PTC7 (25), SIT4 (34), and YVH1 (21). SIT4 and YVH1 have been implicated in the control of virulence-related genes.…”