Trypanosomatid selenophosphate synthetase structure, function and interaction with selenocysteine lyase
Authors: da Silva Marco Túlio Alves , e Silva Ivan Rosa , Faim Lívia Maria , Bellini Natalia Karla , Pereira Murilo Leão , Lima Ana Laura , de Jesus Teresa Cristina Leandro , Costa Fernanda Cristina , Watanabe Tatiana Faria , Pereira Humberto D’Muniz , Valentini Sandro Roberto , Zanelli Cleslei Fernando , Borges Julio Cesar , Bertacine Dias Marcio Vinicius , da Cunha Julia Pinheiro Chagas , Mittra Bidyottam , Andrews Norma W. , Thiemann Otavio Henrique 
Published: January 2020

Early branching eukaryotes have been used as models to study the evolution of cellular molecular processes. Strikingly, human parasite of the Trypanosomatidae family (T. brucei,T. cruziandL. 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 theL. majorselenophosphate 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 complexes involved in the selenocysteine pathway, namely the phosphoseryl-tRNASeckinase (PSTK)-Sec-tRNASecsynthase (SEPSECS) and the tRNASec-specific elongation factor (eEFSec)-ribosome. Endoplasmic reticulum stress with ditiothreitol (DTT) or tunicamycin upon selenophosphate synthetase ablation in procyclicT. bruceicells led to a growth defect. On the other hand, only DTT presented a negative effect in bloodstreamT. bruceiexpressing selenophosphate synthetase-RNAi. Although selenoprotein T (SELENOT) was dispensable for both forms of the parasite, SELENOT-RNAi procyclicT. bruceicells were sensitive to DTT. Together, our data suggest a role for theT. bruceiselenophosphate synthetase in regulation of the parasite’s ER stress response.

Synopsis

Selenium is both a toxic compound and a micronutrient. As a micronutrient, it participates in the synthesis of specific proteins, selenoproteins, as the amino acid selenocysteine. The synthesis of selenocysteine is present in organisms ranging from bacteria to humans. The protozoa parasites of the Trypanosomatidae family, that cause major tropical diseases, conserve the complex machinery responsible for selenocysteine biosynthesis and incorporation in selenoproteins. However, this pathway has been considered dispensable for the protozoa cells. This has intrigued us, and lead to question that if maintained in the cell it should be under selective pressure and therefore be necessary. Also, since the intermediate products of selenocysteine synthesis are toxic to the cell, it has been proposed that these compounds need to be sequestered from the cytoplasm. Therefore, extensive and dynamic protein-protein interactions must happen to deliver those intermediates along the pathway. In this study we have investigated the molecular and structural interactions of different proteins involved in selenocystein synthesis and describe its involvement in the endoplasmic reticulum protection to oxidative stress. Our results also show how the interaction of different proteins leads to the protection of the cell against the toxic effects of seleium compounds during selenocysteine synthesis.