Abstract
Nowadays advanced mass spectrometry techniques make the identification of protein posttranslational modifications (PTMs) much easier than ever before. A series of proteomic studies have demonstrated that large numbers of proteins in cells are modified by phosphorylation, acetylation and many other types of PTMs. However, only limited studies have been performed to validate or characterize those identified modification targets, mostly because PTMs are very dynamic, undergoing large changes in different growth stages or conditions. To overcome this issue, the genetic code expansion strategy has been introduced into PTM studies to genetically incorporate modified amino acids directly into desired positions of target proteins. Without using modifying enzymes, the genetic code expansion strategy could generate homogeneously modified proteins, thus providing powerful tools for PTM studies. In this review, we summarized recent development of genetic code expansion in PTM studies for research groups in this field.
Highlights
Besides 3 stop codons, the genetic code of life contains 61 triplet codons which can encode 20 canonical amino acids
posttranslational modifications (PTMs) happen at multiple sites simultaneously in a single protein and various PTMs could compete with the same amino acid residue, making the characterization of one particular PTM at one specific site difficult
For mono-methylation, Nguyen et al introduced the tert-butyloxycarbonyl (Boc)-methyllysine, which could be removed by acid [72]; Groff et al and Wang et al independently incorporated photocaged Nε-(o-nitrobenzylcarbamoyl)-methyllysine, followed by UV exposure to remove the protecting group [73,74]; Ai et al designed another protected methyllysine, Nε-allylcarbamoylmethyllysine, which could be deprotected by chloro-pentamethylcyclopentadienylcyclooctadieneruthenium (II) [75]
Summary
Besides 3 stop codons, the genetic code of life contains 61 triplet codons which can encode 20 canonical amino acids. In 1956, selenomethionine was first demonstrated to be incorporated into proteins at methionine residues in bacterial cells [6] and lots of amino acid analogs, which could be substrates for the natural translational machinery, were identified to replace their natural counterparts in proteins [7]. Molecules 2018, 23, 1662 identified to replace their natural counterparts in proteins [7] Besides this residue-specific strategy, several approaches have been developed to incorporate noncanonical amino acids (ncAAs) into a have been developed to incorporate noncanonical acids (ncAAs) into aisprotein site-. We focus on its application in PTM studies
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