Fosforilación en células eucarióticas: papel de fosfatasas y quinasas en la biología, patogenia y control de protozoosis tisulares y sanguíneas / Phosphorylation in eukaryotic cells: role of phosphatases and kinases in biology, pathogenesis and control of intracellular and bloodstream protozoa

Cells respond to environmental or cellular changes, rapidly switching protein activities from one state to another. In eukaryotes, a way to achieve these changes is through protein phosphorylation cycles, involving independent protein kinase and protein phosphatase activities. Current evidences show that phosphatases and kinases are also involved in the molecular basis of immune response and in diseases such as diabetes obesity and Alzheimer. In protozoan parasites like Trypanosoma and Leishmania, several kinases and phosphatases have been identified, many of them have been cloned but in several cases their biological role remains undetermined. In this review, the state-of-the art is summarized and the role of phosphatases and kinases in biological phenomena such as remodeling, invasion and pathogenic capacity of protozoan parasites is described. The real chance to use these components of signal transduction pathways as target for chemotherapeutic intervention is also discussed

Searching for the role of protein phosphatases in eukaryotic microorganisms

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

Regulation of different proteolytic pathways in skeletal muscle in fasting and diabetes mellitus

1. Proteins in eukaryotic cells are continually degraded and replaced under precise control mechanisms. Although this continual proteolysis may seem wasteful, it serves several important functions: cells selectively degrade proteins with abnormal sequences or conformations, the accumulation of which could be harmful; the rapid degradation of regulatory peptides and enzymes is essential for the control of metabolic pathways and the cell cycle; and the breakdown of proteins in starvation provides amino acids for gluconeogenesis and energy metabolism. 2. Protein breakdown in eukaryotic cells occurs through distinct pathways: A) lysosomal (involves cathepsins B, H, L, etc.); B) Ca(2+)-dependent (involves Ca(2+)-dependent proteases calpains I and II); C) ATP-dependent, that require or not ubiquitin (comprises at least two large cytosolic proteases, UCDEN and proteasome), and D) ATP-independent (it is not known which proteases are involved in this degradative system). Despite recent dramatic progress, the relative contributions of these pathways to the accelerated proteolysis occurring in normal and pathological states is still largely unknown. 3. In order to identify the cellular mechanisms of skeletal muscle atrophy during fasting and diabetes mellitus, we have studied protein turnover in soleus and EDL muscles from control and fasted (for 24 h) or diabetic rats (1, 3, 5 and 10 days after streptozotocin injection). 4. The increase in muscle proteolysis during fasting seems to be attributable to an enhancement of the energy-requiring process. An increase in the ATP-dependent proteolytic pathway was evident 1 day after food restriction and probably accounted for all of the increased proteolysis demonstrated in the EDL muscles. In parallel with the alterations in the ATP-dependent process, an increase in the ubiquitin-mRNA and proteasome subunit-mRNA was detected. 5. In the acute phase of diabetes (1-3 days) there was an activation of Ca(2+)-dependent (soleus and EDL) and ATP-dependent (EDL) pathways. However, after 5 and 10 days of diabetes the activity of these two pathways fell to values even below control ones. No changes in the lysosomal proteolytic system were observed during diabetes. 6. Although appreciable progress has been made in this research, a large number of important questions remain to be answered, and some of them are discussed in the present paper.

Polirribosilación de proteínas: un mecanismo modulador de funciones celulares / Protein poliribosilation: a modulated mechanism of cellular function

Se presenta una revisión sobre la función de la Poli (ADP-ribosa) sintetasa, enzima nuclear que sintetiza monómeros y polímeros a ADP-ribosas a partir de NAD+, mecanismo denominado polirribosilación. Estas moléculas sintetizadas son unidas covalentemente a proteínas, básicamente histonas, modificando, por ende su funcionalidad. Asímismo, se describen actividades enzimáticas que degradan ADP-ribosas. Se plantean también, los roles que el proceso de polirribosilación, podría modular en el núcleo eucariótico