Trypanosomatid selenophosphate synthetase structure, function and interaction with selenocysteine lyase.

Eukaryotes from the Excavata superphylum have been used as models to study the evolution of cellular molecular processes. Strikingly, human parasites of the Trypanosomatidae family (T. brucei, T. cruzi and L. major) conserve the complex machinery responsible for selenocysteine biosynthesis and incorporation in selenoproteins (SELENOK/SelK, SELENOT/SelT and SELENOTryp/SelTryp), although these proteins do not seem to be essential for parasite viability under laboratory controlled conditions. Selenophosphate synthetase (SEPHS/SPS) plays an indispensable role in selenium metabolism, being responsible for catalyzing the formation of selenophosphate, the biological selenium donor for selenocysteine synthesis. We solved the crystal structure of the L. major selenophosphate synthetase and confirmed that its dimeric organization is functionally important throughout the domains of life. We also demonstrated its interaction with selenocysteine lyase (SCLY) and showed that it is not present in other stable assemblies involved in the selenocysteine pathway, namely the phosphoseryl-tRNASec kinase (PSTK)-Sec-tRNASec synthase (SEPSECS) complex and the tRNASec-specific elongation factor (eEFSec) complex. Endoplasmic reticulum stress with dithiothreitol (DTT) or tunicamycin upon selenophosphate synthetase ablation in procyclic T. brucei cells led to a growth defect. On the other hand, only DTT presented a negative effect in bloodstream T. brucei expressing selenophosphate synthetase-RNAi. Furthermore, selenoprotein T (SELENOT) was dispensable for both forms of the parasite. Together, our data suggest a role for the T. brucei selenophosphate synthetase in the regulation of the parasite's ER stress response.

Hypusine modification of the ribosome-binding protein eIF5A, a target for new anti-inflammatory drugs: understanding the action of the inhibitor GC7 on a murine macrophage cell line.

Inflammation is part of an important mechanism triggered by the innate immune response that rapidly responds to invading microorganisms and tissue injury. One important elicitor of the inflammatory response is the Gram-negative bacteria component lipopolysaccharide (LPS), which induces the activation of innate immune response cells, the release of proinflammatory cytokines, such as interleukin 1 and tumor necrosis factor α(TNF-α), and the cellular generation of nitric oxide (NO) by the inducible nitric oxide synthase (iNOS). Although essential to the immune response, uncontrolled inflammatory responses can lead to pathological conditions, such as sepsis and rheumatoid arthritis. Therefore, identifying cellular targets for new anti-inflammatory treatments is crucial to improving therapeutic control of inflammation-related diseases. More recently, the translation factor eIF5A has been demonstrated to have a proinflammatory role in the release of cytokines and the production of NO. As eIF5A requires and essential and unique modification of a specific residue of lysine, changing it to hypusine, eIF5A is an interesting cellular target for anti-inflammatory treatment. The present study reviews the literature concerning the anti-inflammatory effects of inhibiting eIF5A function. We also present new data showing that the inhibition of eIF5A function by the small molecule GC7 significantly decreases TNF-α release without affecting TNF-α mRNA levels. We discuss the mechanisms by which eIF5A may interfere with TNF-α mRNA translation by binding to and regulating the function of ribosomes during protein synthesis.