Incorporation of Selenocysteine into Proteins Using Peptide Ligation

Abstract

Expressed protein ligation has become a frequently used technique to insert non-standard amino acids into proteins. The technique has been adapted to insert selenocysteine residues in place of cysteine residue in proteins, taking advantage of the similarity in the chemistries of sulfur and selenium. This replacement can confer unique structural and catalytic properties to enzymes and proteins. The development of this technique also allows for naturally occurring selenoproteins to be produced semisynthetically. KeywordsSelenocysteine; expressed protein ligation; thioredoxin reductase; semisynthetic Selenium, the mysterious moon-metalThe Swedish chemist, J.J. Berzilius discovered the 34 th element of the periodic table in 1817 and named it after the Greek goddess of the moon, Selene [1]. It is wholly appropriate that he named this element after the moon-goddess, because selenium, like the moon, has remained mysterious to science until the modern eraThe biological role of selenium began to be realized when Schwarz discovered a dietary factor that was necessary to prevent liver necrosis in rats [2]. He called this mysterious nutritional requirement, "Factor 3". He then determined that this dietary factor was the trace element selenium. In the 1970's, Chinese scientists reported that selenium could prevent a childhood cardiomyopathy known as Keshan disease [3], much like vitamin C can prevent the onset of scurvy. Beck and Levander later showed that both influenza and coxsackie viruses accumulate genetic mutations when these viruses have infected animal hosts that are deficient in selenium or vitamin E [4][5]. Keshan disease is caused when coxsackie virus mutates to a more virulent strain in a host deficient in selenium. In the 1980's, it was discovered that selenium is the only trace element that is incorporated directly into proteins as part of the polypeptide chain. [6]. The incorporation of selenium into proteins, known as selenoproteins, is beginning to explain the important role that selenium plays in human health. A number of important examples can be cited. Selenium is vital to the function of the thyroid gland. The key enzyme in the thyroid gland, which converts thyroxin (T4) to triidothyronine (T3), contains selenium [7]. Selenium is absolutely essential to human male fertility because an enzyme in the testes containing selenium protects developing sperm from oxidative injury [8]. There has long been anecdotal evidence that selenium offers † This work was supported by grant GM070742-01 NIH Public Access Selenium and the split personality of the genetic codeMany of the health benefits of selenium can be explained by its incorporation into proteins as the "21 st " amino acid, selenocysteine [12][13]. This amino acid, though rare, is ubiquitous in all of the kingdoms of life being found in eukarya, prokarya, and archea [14][15]. Examples of selenocysteine-containing proteins are found in plants, fungi, mammals, bacteria, and fish [16]. Like the other standard proteinogenic amino acids, selenocysteine i...

Selenocysteine in Thiol/Disulfide-Like Exchange Reactions

“…Koppenol and coworkers found that at pH 7, a selenolate catalyzed the reduction of a disulfide *390-fold faster than a thiol. This data is not dissimilar from the data reported in (33) at neutral pH [also see (32)]. The authors noted that the difference in nucleophilicity is significantly decreased, to 10-100-fold, to account for differences in the ionization state of the two chalcogens.…”

Studies on deprotection of cysteine and selenocysteine side‐chain protecting groups

“…Our research efforts over the past several years have focused on synthesizing peptides containing selenocysteine (Sec, U) [1] (Abbreviations used in this paper follow the guidelines recommended by Jones JH) for use in peptide ligation reactions [2,3]. One problem with using Sec in solid-phase peptide synthesis (SPPS) is the requirement for using benzyl-type protecting groups for the selenol side-chain owing to the incompatibility of a trityl group (Trt) with this sidechain [4][5][6][7].…”

Synthesis of Selenocysteine and Selenomethionine Derivatives from Sulfur‐Containing Amino Acids

“…According to Scheme 9, the iodination -selenylation protocol was directly applied to lcystine protected with Fmoc groups, 13a, which has a free COOH group. Trapping of the iodide intermediate (18) with the selenolate that was produced by reduction of bis(4-methoxybenzyl) diselenide with NaBH 4 indeed gave the desired product 10 in 12% isolated yield. Although the reaction yield was not remarkably increased compared with the path shown in Scheme 7, the result suggested the compatibility of the S !…”