Penultimate selenocysteine residue replaced by cysteine in thioredoxin reductase from selenium-deficient rat liver

AUTOR(ES)

Lu, Jun

FONTE

The Federation of American Societies for Experimental Biology

RESUMO

Selenium is an essential micronutrient for humans and animals, and its deficiency can predispose to the development of pathological conditions. This study evaluates the effect of selenium deficiency on the thioredoxin system, consisting of NADPH, selenoprotein thioredoxin reductase (TrxR), and thioredoxin (Trx); and the glutathione system, including NADPH, glutathione reductase, glutathione, and glutaredoxin coupled with selenoprotein glutathione peroxidase (GPx). We particularly investigate whether inactive truncated TrxR is present under selenium-starvation conditions due to reading of the UGA codon as stop. Feeding rats a selenium-deficient diet resulted in a large decrease in activity of TrxR and GPx in rat liver but not in the levels of Trx1 and Grx1. However, selenium deficiency induced mitochondrial Grx2 10-fold and markedly changed the expression of some flavoproteins that are involved in the cellular folate, glucose, and lipid metabolism. Liver TrxR mRNA was nearly unchanged, but no truncated enzyme was found. Instead, a low-activity form of TrxR with a cysteine substituted for the penultimate selenocysteine in the C-terminal active site was identified in selenium-deficient rat liver. These results show a novel mechanism for decoding the UGA stop codon, inserting cysteine to make a full-length enzyme that may be required for selenium assimilation.—Lu, J., Zhong, L., Lönn, M. E., Burk, R. F., Hill, K. E., Holmgren, A. Penultimate selenocysteine residue replaced by cysteine in thioredoxin reductase from selenium-deficient rat liver.

Documentos Relacionados

• Expression of glutathione peroxidase I gene in selenium-deficient rats.
• Selenium-deficient diet enhances protein oxidation and affects methionine sulfoxide reductase (MsrB) protein level in certain mouse tissues
• Characterization of Enterovirus Isolates from Patients with Heart Muscle Disease in a Selenium-Deficient Area of China
• Selenocysteine, identified as the penultimate C-terminal residue in human T-cell thioredoxin reductase, corresponds to TGA in the human placental gene.
• Mammalian thioredoxin reductase: Oxidation of the C-terminal cysteine/selenocysteine active site forms a thioselenide, and replacement of selenium with sulfur markedly reduces catalytic activity