If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Locations of Mapped Genes:
|Superclasses:||Biosynthesis → Amino Acids Biosynthesis → Proteinogenic Amino Acids Biosynthesis → L-selenocysteine Biosynthesis|
Selenocysteine has been called the 21st amino acid. It is an essential constituent of three proteins in E. coli: the formate dehydrogenases FDH-O, FDH-N, and FDH-H; each of them contains one selenocysteine residue. The biosynthesis of selenocysteine is unique among amino acid biosyntheses because its defining step occurs while attached to a tRNA molecule. The tRNA molecule, tRNAsec, serves only to insert selenocysteine into these proteins. tRNAsec has an anticodon that recognizes the stop codon UGA; it also has properties that allow it to be charged with serine by the serS-encoded seryl-tRNA synthetase. But it cannot insert serine at an UGA codon. Only after it has been converted to selenocysteyl-tRNAsec by the action of selenocysteine synthetase can it recognize certain UGAs as sense codons and insert selenocysteine there. Recognition of UGA as a sense codon and insertion of selenocysteine depends on adjacent sequences in mRNA termed SECIS (selenocysteine insertion sequence) and a special elongation factor termed SELB, the product of selB, which acts in place of EF-Tu in this special case.
Selenophosphate donates selenium to seryl-tRNAsec thereby converting it to selenocysteyl-tRNAsec. The physiological source of its selenium, shown here as selenide, is not known for certain. Selenite and selenate are transported by the sulfate transporter [LindblowKull85]. Their reduction in vivo to selenide may follow the sulfate reduction path [Muller97, Turner98a]. It has also been suggested that selenium is mobilised from free selenocysteine in vivo by the action of L-cysteine desulfurase [Lacourciere00, Lacourciere02, Ogasawara05a].
Review: Boeck, A and M. Thanbichler, Selenocysteine. EcoSal, Module 188.8.131.52 [Boeck04]
Unification Links: KEGG:map00970
Lacourciere00: Lacourciere GM, Mihara H, Kurihara T, Esaki N, Stadtman TC (2000). "Escherichia coli NifS-like proteins provide selenium in the pathway for the biosynthesis of selenophosphate." J Biol Chem 2000;275(31);23769-73. PMID: 10829016
Lacourciere02: Lacourciere GM (2002). "Selenium is mobilized in vivo from free selenocysteine and is incorporated specifically into formate dehydrogenase H and tRNA nucleosides." J Bacteriol 184(7);1940-6. PMID: 11889101
Ogasawara05a: Ogasawara Y, Lacourciere GM, Ishii K, Stadtman TC (2005). "Characterization of potential selenium-binding proteins in the selenophosphate synthetase system." Proc Natl Acad Sci U S A 102(4);1012-6. PMID: 15653770
Asahara94: Asahara H, Himeno H, Tamura K, Nameki N, Hasegawa T, Shimizu M (1994). "Escherichia coli seryl-tRNA synthetase recognizes tRNA(Ser) by its characteristic tertiary structure." J Mol Biol 236(3);738-48. PMID: 8114091
Baron90: Baron C, Heider J, Bock A (1990). "Mutagenesis of selC, the gene for the selenocysteine-inserting tRNA-species in E. coli: effects on in vivo function." Nucleic Acids Res 18(23);6761-6. PMID: 1702199
Baron91: Baron C, Bock A (1991). "The length of the aminoacyl-acceptor stem of the selenocysteine-specific tRNA(Sec) of Escherichia coli is the determinant for binding to elongation factors SELB or Tu." J Biol Chem 266(30);20375-9. PMID: 1939093
Baron93: Baron C, Westhof E, Bock A, Giege R (1993). "Solution structure of selenocysteine-inserting tRNA(Sec) from Escherichia coli. Comparison with canonical tRNA(Ser)." J Mol Biol 231(2);274-92. PMID: 8510147
Berg91: Berg BL, Baron C, Stewart V (1991). "Nitrate-inducible formate dehydrogenase in Escherichia coli K-12. II. Evidence that a mRNA stem-loop structure is essential for decoding opal (UGA) as selenocysteine." J Biol Chem 266(33);22386-91. PMID: 1834670
Borel94: Borel F, Vincent C, Leberman R, Hartlein M (1994). "Seryl-tRNA synthetase from Escherichia coli: implication of its N-terminal domain in aminoacylation activity and specificity." Nucleic Acids Res 22(15);2963-9. PMID: 8065908
Cusack90: Cusack S, Berthet-Colominas C, Hartlein M, Nassar N, Leberman R (1990). "A second class of synthetase structure revealed by X-ray analysis of Escherichia coli seryl-tRNA synthetase at 2.5 A." Nature 347(6290);249-55. PMID: 2205803
DiazMejia09: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114
Ehrenreich92: Ehrenreich A, Forchhammer K, Tormay P, Veprek B, Bock A (1992). "Selenoprotein synthesis in E. coli. Purification and characterisation of the enzyme catalysing selenium activation." Eur J Biochem 206(3);767-73. PMID: 1606960
Engelhardt92: Engelhardt H, Forchhammer K, Muller S, Goldie KN, Bock A (1992). "Structure of selenocysteine synthase from Escherichia coli and location of tRNA in the seryl-tRNA(sec)-enzyme complex." Mol Microbiol 6(23);3461-7. PMID: 1474891
Eriani90: Eriani G, Delarue M, Poch O, Gangloff J, Moras D (1990). "Partition of tRNA synthetases into two classes based on mutually exclusive sets of sequence motifs." Nature 347(6289);203-6. PMID: 2203971
Forchhammer89: Forchhammer K, Leinfelder W, Bock A (1989). "Identification of a novel translation factor necessary for the incorporation of selenocysteine into protein." Nature 342(6248);453-6. PMID: 2531290
Forchhammer91: Forchhammer K, Leinfelder W, Boesmiller K, Veprek B, Bock A (1991). "Selenocysteine synthase from Escherichia coli. Nucleotide sequence of the gene (selA) and purification of the protein." J Biol Chem 266(10);6318-23. PMID: 2007584
Forchhammer91a: Forchhammer K, Boesmiller K, Bock A (1991). "The function of selenocysteine synthase and SELB in the synthesis and incorporation of selenocysteine." Biochimie 1991;73(12);1481-6. PMID: 1839607
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