Searching for the role of protein phosphatases in eukaryotic microorganisms

Abstract

Preference for specific protein substrates together with differential sensitivity to activators and inhibitors has allowed classification of serine/threonine protein phosphatases (PPs) into four major types designated types 1, 2A, 2B and 2C (PP1, PP2A, PP2B and PP2C, respectively). Comparison of sequences within their catalytic domains has indicated that PP1, PP2A and PP2B are members of the same gene family named PPP. On the other hand, the type 2C enzyme does not share sequence homology with the PPP members and thus represents another gene family, known as PPM. In this report we briefly summarize some of our studies about the role of serine/threonine phosphatases in growth and differentiation of three different eukaryotic models: Blastocladiella emersonii, Neurospora crassa and Dictyostelium discoideum. Our observations suggest that PP2C is the major phosphatase responsible for dephosphorylation of amidotransferase, an enzyme that controls cell wall synthesis during Blastocladiella emersonii zoospore germination. We also report the existence of a novel acid-and thermo-stable protein purified from Neurospora crassa mycelia, which specifically inhibits the PP1 activity of this fungus and mammals. Finally, we comment on our recent results demonstrating that Dictyostelium discoideum expresses a gene that codes for PP1, although this activity has never been demonstrated biochemically in this organism.

Searching for Excystment‐Regulated Genes in Sterkiella histriomuscorum (Ciliophora, Oxytrichidae): A mRNA Differential Display Analysis of Gene Expression in Excysting Cells

“…However, we favour the idea that PP2C could be involved in the encystment/ excystment cellular differentiation program, even though this transcript seems not to be tightly regulated during this part of the life cycle. This hypothesis is based on recent studies on eukaryotic microorganisms, in which phosphatase 2C enzymes have been implicated in fundamental mechanisms of cellular growth and differentiation, as for instance zoospore germination in Blastocladiella (da‐Silva et al 1999).…”

Biochemical Properties and Possible Roles of Ectophosphatase Activities in Fungi

“…Thus, phosphorylation and dephosphorylation of proteins is related to several fundamental biological processes in fungi, such as the cell cycle, transcription and cell differentiation [5,6]. Furthermore, these enzymes are involved in other cellular processes, such as cell wall synthesis [7], formation of hyphae [8] and maintenance of cellular integrity in stress situations [9–11].…”

Regulation of metabolism in estivating land snails: role of reversible protein phosphorylation

“…Phosphatases with type-2B activity have been isolated and studied in the unicellular organisms Dictyostelium discoideum (Hellstem et al, 1997), Paramecium tetraurelia (Kissmehl et al, 1997), and Leishmania donovani (Banerjee et al, 1999); PP2B has also been identified in several mollusc models, primarily in neural or smooth muscle tissues (Krinks et al, 1988;Inoue et al, 1990;Sharma et al, 2003;Yamada et al, 2004). While PP2C has not been extensively studied outside of mammals, type-2C phosphatases have been characterized in yeast (Shiozaki and Russell, 1994), D. melanogaster (Baril and Therrien, 2006), and several microorganisms (Bums et al, 1993;Klumpp et al, 1994;Grothe et al, 1998;Da Silva et al, 1999).…”