Tagging recombinant proteins with a Sel-tag for purification, labeling with electrophilic compounds or radiolabeling with 11C

Nat Protoc. 2006;1(2):604-13. doi: 10.1038/nprot.2006.87. Epub 2006 Jul 6.


Selenocysteine (Sec; U in one-letter code) is the twenty-first naturally occurring amino acid, with a selenium atom that gives this cysteine (Cys) homolog unique biochemical properties, including a high nucleophilicity and significant reactivity with electrophilic agents. This can be used in biotechnological Sec-dependent applications. Here, we describe how Sec can be introduced into a carboxy-terminal tetrapeptide motif (-Gly-Cys-Sec-Gly-COOH, known as a Sel-tag) for recombinant proteins by tailoring the encoding gene to become compatible with the Escherichia coli selenoprotein synthesis machinery. We also describe how the Sel-tag can be used as a basis for efficient one-step protein purification, rapid Sec-targeting protein labeling with electrophilic compounds, or radiolabeling with the positron emitter 11C.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carbon Radioisotopes
  • Escherichia coli
  • Gene Expression Regulation, Bacterial
  • Isotope Labeling / methods*
  • Protein Conformation
  • Recombinant Proteins / analysis*
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / isolation & purification*
  • Selenocysteine / chemistry*
  • Selenoproteins / metabolism


  • Carbon Radioisotopes
  • Recombinant Proteins
  • Selenoproteins
  • Selenocysteine