Estudos moleculares das enzimas envolvidas na biossíntese de selenocisteína em Trypanosoma brucei e Leishmania major / Molecular studies of the enzymes involved in selenocysteine synthesis in Trypanosoma brucei and Leishmania major

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

One of the main biological forms of the selenium incorporation is the amino acid form named selenocysteine (Sec, U), which is incorporated co-translationally at the emerging new polypeptide in the specific positions at the UGA codon, that is usually recognized as stop codon. The incorporation of the selenocysteine in E.coli is already solved with the involvement of the genes that codify to selenocysteine synthase (SELA), seryl tRNA synthetase (SerRS), a specific tRNASec (SELC), selenophosphate synthetase (SELD) and a selenocysteine-specific translation elongation factor (SELB). However, in eukarya there is no SELA homologue, but there are evidences about the requirement of the two enzymatic steps that replace the activity performed by SELA, the fosforilation of the serine followed by selenocysteylation through the phosphoseryl-tRNASec kinase (PSTK) and Sep-tRNA:Sec-tRNA synthase (SepSecS) enzymes, respectively. Currently, the selenocysteine synthesis and its incorporation is more studied in many organisms, but less explored in Kinetoplastid. Subsequently, the molecular studies were done with the enzymes involved in this pathway, especially in Trypanosoma brucei and Leishmania major. The SECIS element was identified in the region 3´ of the mRNA, that acts in the recognition of the UGA codon positioned within a genes open reading frame on the insertion of the selenocysteine in Leishmania major and Leishmania infantum; the incorporation of 75Se into Leishmania proteins, the occurrence of selenocysteine-tRNASec in both Leishmania and Trypanosoma; in addition, the finding of all genes necessary for selenocysteine synthesis, such as: SELB, SELD, PSTK, and SECp43. Clones were obtained from the selB and selD genes in the pET28a(+) expression vector and the enzymes were expressed in Escherichia coli BL21 (DE3). The recombinant SELD protein was purified by affinity chromatography and its pI and molecular mass were determined using: isoeletrophocusing electrophoresis and native gel. The proteins SELB, SELD, SECp43, and sery-tRNA synhetase were immune located in the cytoplasm in T. brucei native cells. A new methodology "PTP tagging" was utilized for protein interaction studies by using target proteins SECp43, SELB and PSTK to search new tagged proteins in selenocysteine T. brucei synthesis. Future molecular and structural investigation of the enzymes involved in Kinetoplastida selenocysteine biosynthesis will provide relevant information for understanding of the synthesis of this amino acid as well as the development of the specific inhibitors, focusing the treatment of the disease caused by Trypanosoma brucei e Leishmania major parasites.

ASSUNTO(S)

kinetoplastida proteins selenocisteína proteínas selenocysteine kinetoplastid

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