Photo-reactive amino acid analog

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Photo-reactive amino acid analogs for in-vivo crosslinking of protein complexes were introduced in 2005 by researchers from the Max Planck Institute [1] In this method, cells are grown with photoreactive diazirine analogs to leucine and methionine, which are incorporated into proteins. Upon exposure to ultraviolet light, the diazirines are activated and bind to interacting proteins that are within a few angstroms of the photo-reactive amino acid analog.

L-Photo-Leucine and L-Photo-Methionine are analogs of the naturally occurring L-Leucine and L-Methionine amino acids that are endogenously incorporated into the primary sequence of proteins during synthesis using the normal translation machinery. They are then ultraviolet light (UV)-activated to covalently crosslink proteins within protein-protein interaction domains in their native in-vivo environment. The method enables the determination and characterization of both stable and transient protein interactions in cells without the addition of chemical crosslinkers and associated solvents that can adversely affect the cell biology being studied in the experiment.

When used in combination with limiting media that is devoid of leucine and methionine, the photo-activatable derivatives are treated like naturally occurring amino acids by the cellular protein synthesis machinery. As a result, they can be substituted for leucine or methionine in the primary structure of proteins. Photo-leucine and photo-methionine derivatives contain diazirine rings that are activated when exposed to UV light to become reactive intermediates that form covalent bonds with nearby protein side chains and backbones. Naturally interacting proteins within the cell can be instantly trapped by photoactivation of the diazirine-containing proteins in the cultured cells. Crosslinked protein complexes can be detected by decreased mobility on SDS-PAGE followed by Western blotting, size exclusion chromatography, sucrose density gradient sedimentation or mass spectrometry.


  1. Suchanek, M., Radzikowska, A., and Thiele, C. (2005). "Photo-leucine and photo-methionine allow identification of protein-protein interactions in living cells". Nature Methods. 2: 261–268. PMID 15782218.
  • Vila-Perello, M., et al. (2007). Covalent capture of phospho-dependent protein oligomerization by site-specific incorporation of a diazirine photo-cross-linker. J. Am. Chem. Soc., 129(26):8068-8069.
  • Bomgarden, R. (2008). Studying Protein Interactions in Living Cells. Gen. Eng. News. Vol. 28, No. 7. [2]