Remarkable progress has occurred in many branches of biology and health sciences during the last few decades. Trace element (TE) research has definitely shared in this explosion of scientific knowledge. Due to the imp...Remarkable progress has occurred in many branches of biology and health sciences during the last few decades. Trace element (TE) research has definitely shared in this explosion of scientific knowledge. Due to the improvements in analytical technology, the discovery of TEs in organism was realized. The developments of TE research have been promoted by the demand of public health (e.g. deficiency or toxicity). The profound knowledge of nutritional importance of TEs has been achieved with application of advanced methods in biological, medical and chemical fields, etc. In this paper, a new definition of essentiality of TEs is introduced. According to this definition, onIy ten TEs (Fe, Zn, F, Cu, I, Se, Mn, Mo, Cr, Co) are considered to be essential to humans. The others need more evidence to prove their essentiality in humans. The recent progress on the biochemical and immunological functions of TEs and on the roles of TEs in brain development are briefly described. The TEs, mainly Se, I, Zn, Fe, are more closely related to public health. Also, emphases are laid on balancing all nutrients when new knowledge of essential TEs is applied in public health展开更多
Selenium has been recognized as an essential nutrient in animals since the 1950s. Demonstration of the role of dietary selenium in protection from oxidative stress foIlowed in the early 1970s, and was largely attribut...Selenium has been recognized as an essential nutrient in animals since the 1950s. Demonstration of the role of dietary selenium in protection from oxidative stress foIlowed in the early 1970s, and was largely attributed to its presence as an integral part of cellular glutathione peroxidase. However, the functions of this enzyme did not explain many of the other effects of selenium deficiency. The identification of other mammalian selenoproteins during the last few years has provided new insights into the functions of this trace nutrient. The discovery that type 1 deiodinase (D1) is a selenoenzyme, in addition to unveiling an essential role for selenium in thyroid hormone action, has had more far-reaching implications. Studies of this protein opened the door for investigation of the requirements for eukaryotic selenoprotein synthesis,and the features that distinguish this pathway from the corresponding prokaryotic pathway.Selenium is present in a number of prokaryotic and eukaryotic proteins in the form of the unusual amino acid, selenocysteine. Incorporation of selenocysteine into these proteins requires a novel translation step in which UGA specifies selenocysteine insertion. Since UGA codons are typically recognized as translation stop signals, an intriguing question is raised: How does a cell recognize and distinguish a UGA selenocysteine codon from a UGA stop codon? In this review, we will focus on what is known about selenocysteine incorporation in eukaryotes, briefly summarizing initial studies and discussing a few recent advances in our understanding of this unique 'recoding' process展开更多
Selenocysteine, a selenium-containing analog of cysteine, is found in the prokaryotic and eukaryotic kingdoms in active sites of enzymes involved in oxidation-reduction reactions. This aminoacid is cotranslationally i...Selenocysteine, a selenium-containing analog of cysteine, is found in the prokaryotic and eukaryotic kingdoms in active sites of enzymes involved in oxidation-reduction reactions. This aminoacid is cotranslationally incorporated at UGA codons which usually act as translation stop codons. In eukaryotes, decoding of selenocysteine necessitates the participation of the selenocysteine insertion sequence (SECIS), an element lying in the 3' -untranslated region of selenoprotein mRNAs. A detailed experimental study of the secondary structures of the SECIS elements of rat and human type 1 iodothyronine deiodinases and rat glutathione peroxidase was performed. Enzymatic and chemical structure probing led us to propose a secondary structure model, supported by sequence comparison of 23 SECIS mRNAs. The secondary structure model revealed the existence of a novel type of RNA motif composed of four consecutive non-Watson-Crick base-pairs. Using gel shift experiments, we identified in several mammalian cell type extracts the protein SBP,for SECIS-binding protein, that specifically recognizes the iodothyronine deiodinases and glutathione peroxidase SECIS elements. The structural model that we derived for the SECIS RNAs discloses RNA features possibly implicated in the binding of SBP and/or SECIS function展开更多
Incorporation of Selenocysteine into protein requires an RNA structural motif, SECIS (Selenocysteine insertion sequence) element that, along with other factors, demarcates UGA-Sec from the UGA termination codon, for e...Incorporation of Selenocysteine into protein requires an RNA structural motif, SECIS (Selenocysteine insertion sequence) element that, along with other factors, demarcates UGA-Sec from the UGA termination codon, for expression of Selenoproteins (in case of eukaryotes). It has been predicted that during HIV infection, several functional viral selenoproteins are expressed and synthesis of these viral selenoproteins deplete the selenium level of the host. It might be that even the viral genome has the SECIS elements in their Selenoprotein mRNA, and during infection, the host cellular machinery is transformed in such a way that the human Sec tRNA binds to the viral Selenoprotein mRNA, instead of binding to its own Selenoprotein mRNA, thus leading to expression of viral selenoproteins. This hypothesis was tested in this study by identifying the SECIS elements in the HIV-1 genome and further predicting their secondary and tertiary structures. We then tried to dock these tertiary structures with human Sec tRNA. Here we report putatively the presence of 3215 SECIS elements in the HIV-1 genome and that the human Sec tRNAsec binds to the viral SECIS elements present in the viral selenoprotein mRNA. Based on an earlier finding, it was observed that atoms of A8 and U9, which present in human Sec tRNA, are the possible key sites for binding.展开更多
文摘Remarkable progress has occurred in many branches of biology and health sciences during the last few decades. Trace element (TE) research has definitely shared in this explosion of scientific knowledge. Due to the improvements in analytical technology, the discovery of TEs in organism was realized. The developments of TE research have been promoted by the demand of public health (e.g. deficiency or toxicity). The profound knowledge of nutritional importance of TEs has been achieved with application of advanced methods in biological, medical and chemical fields, etc. In this paper, a new definition of essentiality of TEs is introduced. According to this definition, onIy ten TEs (Fe, Zn, F, Cu, I, Se, Mn, Mo, Cr, Co) are considered to be essential to humans. The others need more evidence to prove their essentiality in humans. The recent progress on the biochemical and immunological functions of TEs and on the roles of TEs in brain development are briefly described. The TEs, mainly Se, I, Zn, Fe, are more closely related to public health. Also, emphases are laid on balancing all nutrients when new knowledge of essential TEs is applied in public health
文摘Selenium has been recognized as an essential nutrient in animals since the 1950s. Demonstration of the role of dietary selenium in protection from oxidative stress foIlowed in the early 1970s, and was largely attributed to its presence as an integral part of cellular glutathione peroxidase. However, the functions of this enzyme did not explain many of the other effects of selenium deficiency. The identification of other mammalian selenoproteins during the last few years has provided new insights into the functions of this trace nutrient. The discovery that type 1 deiodinase (D1) is a selenoenzyme, in addition to unveiling an essential role for selenium in thyroid hormone action, has had more far-reaching implications. Studies of this protein opened the door for investigation of the requirements for eukaryotic selenoprotein synthesis,and the features that distinguish this pathway from the corresponding prokaryotic pathway.Selenium is present in a number of prokaryotic and eukaryotic proteins in the form of the unusual amino acid, selenocysteine. Incorporation of selenocysteine into these proteins requires a novel translation step in which UGA specifies selenocysteine insertion. Since UGA codons are typically recognized as translation stop signals, an intriguing question is raised: How does a cell recognize and distinguish a UGA selenocysteine codon from a UGA stop codon? In this review, we will focus on what is known about selenocysteine incorporation in eukaryotes, briefly summarizing initial studies and discussing a few recent advances in our understanding of this unique 'recoding' process
文摘Selenocysteine, a selenium-containing analog of cysteine, is found in the prokaryotic and eukaryotic kingdoms in active sites of enzymes involved in oxidation-reduction reactions. This aminoacid is cotranslationally incorporated at UGA codons which usually act as translation stop codons. In eukaryotes, decoding of selenocysteine necessitates the participation of the selenocysteine insertion sequence (SECIS), an element lying in the 3' -untranslated region of selenoprotein mRNAs. A detailed experimental study of the secondary structures of the SECIS elements of rat and human type 1 iodothyronine deiodinases and rat glutathione peroxidase was performed. Enzymatic and chemical structure probing led us to propose a secondary structure model, supported by sequence comparison of 23 SECIS mRNAs. The secondary structure model revealed the existence of a novel type of RNA motif composed of four consecutive non-Watson-Crick base-pairs. Using gel shift experiments, we identified in several mammalian cell type extracts the protein SBP,for SECIS-binding protein, that specifically recognizes the iodothyronine deiodinases and glutathione peroxidase SECIS elements. The structural model that we derived for the SECIS RNAs discloses RNA features possibly implicated in the binding of SBP and/or SECIS function
文摘Incorporation of Selenocysteine into protein requires an RNA structural motif, SECIS (Selenocysteine insertion sequence) element that, along with other factors, demarcates UGA-Sec from the UGA termination codon, for expression of Selenoproteins (in case of eukaryotes). It has been predicted that during HIV infection, several functional viral selenoproteins are expressed and synthesis of these viral selenoproteins deplete the selenium level of the host. It might be that even the viral genome has the SECIS elements in their Selenoprotein mRNA, and during infection, the host cellular machinery is transformed in such a way that the human Sec tRNA binds to the viral Selenoprotein mRNA, instead of binding to its own Selenoprotein mRNA, thus leading to expression of viral selenoproteins. This hypothesis was tested in this study by identifying the SECIS elements in the HIV-1 genome and further predicting their secondary and tertiary structures. We then tried to dock these tertiary structures with human Sec tRNA. Here we report putatively the presence of 3215 SECIS elements in the HIV-1 genome and that the human Sec tRNAsec binds to the viral SECIS elements present in the viral selenoprotein mRNA. Based on an earlier finding, it was observed that atoms of A8 and U9, which present in human Sec tRNA, are the possible key sites for binding.
