title: Identification and characterization of a selenoprotein family containing a diselenide bond in a redox motif.
abstract: Selenocysteine (Sec, U) insertion into proteins is directed by translational recoding of specific UGA codons located upstream of a stem-loop structure known as Sec insertion sequence (SECIS) element. Selenoproteins with known functions are oxidoreductases containing a single redox-active Sec in their active sites. In this work, we identified a family of selenoproteins, designated SelL, containing two Sec separated by two other residues to form a UxxU motif. SelL proteins show an unusual occurrence, being present in diverse aquatic organisms, including fish, invertebrates, and marine bacteria. Both eukaryotic and bacterial SelL genes use single SECIS elements for insertion of two Sec. In eukaryotes, the SECIS is located in the 3' UTR, whereas the bacterial SelL SECIS is within a coding region and positioned at a distance that supports the insertion of either of the two Sec or both of these residues. SelL proteins possess a thioredoxin-like fold wherein the UxxU motif corresponds to the catalytic CxxC motif in thioredoxins, suggesting a redox function of SelL proteins. Distantly related SelL-like proteins were also identified in a variety of organisms that had either one or both Sec replaced with Cys. Danio rerio SelL, transiently expressed in mammalian cells, incorporated two Sec and localized to the cytosol. In these cells, it occurred in an oxidized form and was not reducible by DTT. In a bacterial expression system, we directly demonstrated the formation of a diselenide bond between the two Sec, establishing it as the first diselenide bond found in a natural protein.
authors: Department of Biochemistry, University of Nebraska, Lincoln, NE 68588-0664, USA.
authors: Valentina A
authors: VA
authors: Shchedrina
authors: Sergey V
authors: SV
authors: Novoselov
authors: Mikalai Yu
authors: MY
authors: Malinouski
authors: Vadim N
authors: VN
authors: Gladyshev
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D004251:DNA Transposable Elements / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020224:Expressed Sequence Tags; D016680:Genome, Bacterial; D006801:Humans; D007668:Kidney; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017279:Selenocysteine; D051140:Selenoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013438:Sulfhydryl Compounds; D014162:Transfection; D015027:Zebrafish / Q000235:genetics
chemical_list: D004251:DNA Transposable Elements; D029968:Escherichia coli Proteins; D011994:Recombinant Proteins; D051140:Selenoproteins; D013438:Sulfhydryl Compounds; D017279:Selenocysteine
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