|Gene:||selB||Accession Numbers: EG10942 (MetaCyc), b3590, ECK3579|
Species: Escherichia coli K-12 substr. MG1655
Component of: SelB-L-selenocysteinyl-tRNAsec
SelB is a specialized translation factor that takes the place of elongation factor EF-Tu for the insertion of selenocysteine into a peptide chain at the site of a UGA codon. Most UGA codons signal chain termination; a UGA codon that encodes selenocysteine insertion is distinguished from those that signal chain termination by a structured sequence, called SECIS (SElenoCysteine Insertion Sequence), immediately downstream of the UGA codon [Heider92, Chen93f]. SelB recognizes and binds to identical bases within the loop region in the SECIS hairpin structure of both fdhF and fdnG mRNAs, and thereby brings the charged selenocysteyl-tRNASec (Sec-tRNASec) into the neighborhood of the UGA codon [Baron93, Ringquist94, Huttenhofer96].
SelB is found at a level of approximately 1100 copies per cell [Forchhammer90].
The N-terminal domain of SelB shares extensive sequence similarity with EF-Tu and IF2 [Forchhammer89]; this domain binds specifically to Sec-tRNASec [Kromayer96]. Its structure was modeled based on that of Thermus thermophilus EF-Tu [Hilgenfeld96]. Like EF-Tu, SelB binds GTP and exhibits a low GTPase activity which is stimulated by the presence of 70S ribosomes and the SECIS element [Huttenhofer98]. An additional C-terminal domain of SelB consisting of four tandem winged-helix motifs is responsible for binding to the SECIS mRNA structure [Kromayer96]. Suppressor mutations within selB that suppress the effect of defined mutations within the SECIS element have been isolated [Kromayer99, Li00b].
The kinetics of the interactions of SelB with guanosine nucleotides, the SECIS element, and Sec-tRNASec have been studied, shedding light on the mechanism of SelB action compared to the standard elongation factor EF-Tu [Thanbichler00, Paleskava10].
The length of the aminoacyl-acceptor stem of tRNASec is a specificity determinant for SelB binding [Baron91], and the selenol group of the aminoacylated tRNASec is required for stable interaction between SelB and Sec-tRNASec [Forchhammer91]. A crystal structure of a fragment of SelB in complex with the hairpin SECIS element has been solved at 2.3 Å resolution [Soler07].
A selB mutant accumulates Sec-tRNASecUCA and does not incorporate selenocysteine into selenoproteins [Leinfelder89].
SelB is able to autoregulate the expression of the selAB operon at the posttranscriptional level. SelB binds to a SECIS-like element upstream of the selA ribosome binding site, affecting the stability and translation of the selAB mRNA [Thanbichler02].
SelB: "selenium metabolism" [Leinfelder88]
|Map Position: [3,756,040 <- 3,757,884]|
Molecular Weight of Polypeptide: 68.867 kD (from nucleotide sequence)
Unification Links: ASAP:ABE-0011729 , CGSC:17890 , DIP:DIP-10848N , EchoBASE:EB0935 , EcoGene:EG10942 , EcoliWiki:b3590 , Mint:MINT-1221874 , ModBase:P14081 , OU-Microarray:b3590 , PortEco:selB , Pride:P14081 , Protein Model Portal:P14081 , RefSeq:NP_418047 , RegulonDB:EG10942 , SMR:P14081 , String:511145.b3590 , UniProt:P14081
Relationship Links: InterPro:IN-FAMILY:IPR000795 , InterPro:IN-FAMILY:IPR004161 , InterPro:IN-FAMILY:IPR004535 , InterPro:IN-FAMILY:IPR009000 , InterPro:IN-FAMILY:IPR009001 , InterPro:IN-FAMILY:IPR011991 , InterPro:IN-FAMILY:IPR015190 , InterPro:IN-FAMILY:IPR015191 , InterPro:IN-FAMILY:IPR027417 , PDB:Structure:2PJP , Pfam:IN-FAMILY:PF00009 , Pfam:IN-FAMILY:PF03144 , Pfam:IN-FAMILY:PF09106 , Pfam:IN-FAMILY:PF09107 , Prints:IN-FAMILY:PR00315 , Prosite:IN-FAMILY:PS00301
|Biological Process:||GO:0001514 - selenocysteine incorporation
GO:0016259 - selenocysteine metabolic process [Leinfelder88]
GO:0006412 - translation [UniProtGOA11a]
|Molecular Function:||GO:0000049 - tRNA binding
GO:0003924 - GTPase activity [GOA01a, Huttenhofer98]
GO:0005525 - GTP binding [UniProtGOA11a, GOA01a, Forchhammer89]
GO:0019003 - GDP binding [Forchhammer89]
GO:0035368 - selenocysteine insertion sequence binding [Baron93]
GO:0000166 - nucleotide binding [UniProtGOA11a]
GO:0003746 - translation elongation factor activity [GOA01a]
|Cellular Component:||GO:0005737 - cytoplasm
[UniProtGOA11, UniProtGOA11a, GOA01a]
GO:0005829 - cytosol
|MultiFun Terms:||information transfer → protein related → translation|
Enzymatic reaction of: GTPase (selenocysteyl-tRNA-specific translation elongation factor)
EC Number: 126.96.36.199/188.8.131.52/184.108.40.206/220.127.116.11/18.104.22.168/22.214.171.124
The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.
The reaction is physiologically favored in the direction shown.
The GTPase activity of SelB is stimulated by the presence of the 70S ribosome and the SECIS element [Huttenhofer98].
Subunit of: SelB-L-selenocysteinyl-tRNAsec
Species: Escherichia coli K-12 substr. MG1655
Subunit composition of
SelB-L-selenocysteinyl-tRNAsec = [SelB][L-selenocysteinyl-tRNAsec]
selenocysteyl-tRNA-specific translation elongation factor = SelB (extended summary available)
|Conserved-Region||1 -> 173|
|Nucleotide-Phosphate-Binding-Region||7 -> 14|
|Protein-Segment||35 -> 39|
|Protein-Segment||57 -> 60|
|Nucleotide-Phosphate-Binding-Region||57 -> 61|
|Nucleotide-Phosphate-Binding-Region||112 -> 115|
|Protein-Segment||147 -> 149|
10/20/97 Gene b3590 from Blattner lab Genbank (v. M52) entry merged into EcoCyc gene EG10942.
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
Bock97: Bock A, Hilgenfeld R, Tormay P, Wilting R, Kromayer M (1997). "Domain structure of the selenocysteine-specific translation factor SelB in prokaryotes." Biomed Environ Sci 10(2-3);125-8. PMID: 9315303
Chen93f: Chen GF, Fang L, Inouye M (1993). "Effect of the relative position of the UGA codon to the unique secondary structure in the fdhF mRNA on its decoding by selenocysteinyl tRNA in Escherichia coli." J Biol Chem 268(31);23128-31. PMID: 8226830
Fagegaltier01: Fagegaltier D, Carbon P, Krol A (2001). "Distinctive features in the SelB family of elongation factors for selenoprotein synthesis. A glimpse of an evolutionary complexified translation apparatus." Biofactors 14(1-4);5-10. PMID: 11568434
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
Forchhammer90: Forchhammer K, Rucknagel KP, Bock A (1990). "Purification and biochemical characterization of SELB, a translation factor involved in selenoprotein synthesis." J Biol Chem 265(16);9346-50. PMID: 2140572
Forchhammer91: Forchhammer K, Boesmiller K, Bock A (1991). "The function of selenocysteine synthase and SELB in the synthesis and incorporation of selenocysteine." Biochimie 73(12);1481-6. PMID: 1839607
Heider92: Heider J, Baron C, Bock A (1992). "Coding from a distance: dissection of the mRNA determinants required for the incorporation of selenocysteine into protein." EMBO J 11(10);3759-66. PMID: 1396569
Huttenhofer96: Huttenhofer A, Westhof E, Bock A (1996). "Solution structure of mRNA hairpins promoting selenocysteine incorporation in Escherichia coli and their base-specific interaction with special elongation factor SELB." RNA 2(4);354-66. PMID: 8634916
Kromayer99: Kromayer M, Neuhierl B, Friebel A, Bock A (1999). "Genetic probing of the interaction between the translation factor SelB and its mRNA binding element in Escherichia coli." Mol Gen Genet 262(4-5);800-6. PMID: 10628863
Leinfelder88: Leinfelder W, Forchhammer K, Zinoni F, Sawers G, Mandrand-Berthelot MA, Bock A (1988). "Escherichia coli genes whose products are involved in selenium metabolism." J Bacteriol 170(2);540-6. PMID: 2962989
Li00b: Li C, Reches M, Engelberg-Kulka H (2000). "The bulged nucleotide in the Escherichia coli minimal selenocysteine insertion sequence participates in interaction with SelB: a genetic approach." J Bacteriol 182(22);6302-7. PMID: 11053373
Paleskava10: Paleskava A, Konevega AL, Rodnina MV (2010). "Thermodynamic and kinetic framework of selenocysteyl-tRNASec recognition by elongation factor SelB." J Biol Chem 285(5);3014-20. PMID: 19940162
Ringquist94: Ringquist S, Schneider D, Gibson T, Baron C, Bock A, Gold L (1994). "Recognition of the mRNA selenocysteine insertion sequence by the specialized translational elongation factor SELB." Genes Dev 8(3);376-85. PMID: 8314089
Thanbichler00: Thanbichler M, Bock A, Goody RS (2000). "Kinetics of the interaction of translation factor SelB from Escherichia coli with guanosine nucleotides and selenocysteine insertion sequence RNA." J Biol Chem 275(27);20458-66. PMID: 10781605
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