Photoaffinity labelling

Dorman G (2000) Photoaffinity Labeling in Biological Signal Transduction. 211 169-225 Drabowicz J, Mikolajczyk M (2000) Selenium at Higher Oxidation States. 208 143-176 Eder B, see Wrodnigg TM (2001) The Amadori and Heyns Rearrangements Landmarks in the History of Carbohydrate Chemistry or Unrecognized Synthetic Opportunities 215 115-175... 

A photoaffinity label is a molecule that forms a highly reactive excited state when illuminated with light of an appropriate wavelength. While in this excited state the photoaffinity label can covalently modify groups on the enzyme molecule that are in close proximity to the label. Hence one can mix the compound and enzyme... 

Figure 8.19 Examples of photoaffinity labels. (A) An aryl azide and (B) a benzophenone.

Photoaffinity labeling can be particularly useful when dealing with noncompetitive inhibitors, where the site of binding cannot be inferred from competition with specific substrate or cofactor molecules. 

Figure 8.20 (A) Generic chemical structure of the y-secretase inhibitors described by Seiffert et al. (2000). (B) y-Secretase inhibitor incorporating a benzophenone photoaffinity label for crosslinking studies.

In addition to its interaction with central BZD receptors, pharmacological concentrations of melatonin can also bind to the peripheral-type BZ receptors (PBRs), which are involved in neurosteroidogenesis (Garcia-Ovejero et al. 2005). PBRs are primarily localized on the outer mitochondrial membrane these sites are therefore also referred to as mitochondrial BZD receptors. Using the isoquinoline carboxamide, PK14105, for photoaffinity labelling, an 18 kDa isoquinoline... 

Wieland, T., et al. Identity of hepatic membrane transport systems for bile salts, phalloidin, and antamanide by photoaffinity labeling. Proc. Natl. Acad. Sci. U. S. A. 1984, 81, 5232-5236. 

Several papers in the last two years attempted to separate the photoreceptor-flavin (and/or the associated b-type cytochrome) from the overwhelming amount of bulk-flavin which is involved in metabolism rather than photoreception. However, a clear-cut assay for the bluelight receptor has not yet been found. Specific photoaffinity labeling and the considerable selectivity in the photoreduction of a b-type cytochrome, as mediated by suitable dyes, are the most promising attempts. 

PNP-DTP has been used to photoaffinity label the thyroid hormone nuclear receptors in intact cells by preparing a derivative of 3,5,3 -triiodo-L-thyronine with the crosslinker (Pascual et al., 1982 Casanova et al., 1984). Effective photoreactive conjugation was found to occur after irradiation with UV light at 254 or 310 nm. 

Campbell, R, and Gioannini, T.L. (1979) The use of benzophenone as a photoaffinity label. Labeling in p-benzoylphenylacetyl chymotrypsin at unit efficiency. Photochem. Photobiol. 29, 883. 

Casanova, J., Horowitz, Z.D., Copp, R.R, Nclntyre, W.R., Pascual, A., and Samuels, H.H. (1984) Photoaffinity labeling of thyroid hormone nuclear receptors./. Biol. Ghent. 259, 12084-12091. 

Chowdhry, V., Vaughn, R., and Westheimer, F.H. (1976) 2-Diazo-3,3,3-trifluoropropionyl chlorides Reagent for photoaffinity labeling. Proc. Natl. Acad. Sci. USA 73, 1406-1408. 

Galardy, R.E., Craig, L.C., Jamieson, J.D., and Printz, M.P. (1974) Photoaffinity labeling of peptide hormone binding sites./. Biol. Chem. 249, 3510-3518. 

Horney, M.J. et al. (2001) Synthesis and characterization of insulin-like growth factor (IGF)-l photoprobes selective for the IgG-binding proteins (IGFBPs) photoaffinity labeling of the IGF-binding domain on IGFBP-2./. Biol. Chem. 276(4), 2880-2889. 

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