title: Element-coded affinity tags for peptides and proteins.
abstract: Isotope-coded affinity tags (ICAT) represent an important new tool for the analysis of complex mixtures of proteins in living systems [Aebersold, R., and Mann, M. (2003) Nature, 422, 198-207]. We envisage an alternative protein-labeling technique based on tagging with different element-coded metal chelates, which affords affinity chromatography, quantification, and identification of a tagged peptide from a complex mixture. As proof of concept, a synthetic peptide was modified at a cysteine side chain with either a carboxymethyl group or acetamidobenzyl-1,4,7,10-tetraazacyclododecane-N,N',N' ',N' "-tetraacetic acid (AcBD) chelates of terbium or yttrium. A mixture of the three modified peptides in a mole ratio of 100:1.0:0.83 carboxymethyl:AcBD-Tb:AcBD-Y was trypsinized, purified on a new affinity column that binds rare-earth DOTA chelates, and analyzed by LC-MS/MS. Chelate-tagged tryptic peptides eluted cleanly from the affinity column; the tagged peptides chromatographically coeluted during LC-MS analysis, were present in the expected ratio as indicated by MS ion intensity, and were sequence-identified by tandem mass spectrometry. DOTA-rare earth chelates have exceptional properties for use as affinity tags. They are highly polar and water-soluble. Many of the rare earth elements are naturally monoisotopic, providing a variety of simple choices for preparing mass tags. Further, the rare earths are heavy elements, whose mass defects give the masses of tagged peptides exact values not normally shared by molecules that contain only light elements.
authors.affiliation: Department of Chemistry, University of California, One Shields Avenue, Davis, California 95616, USA.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Whetstone
authors.forename: Nathaniel G
authors.initials: NG
authors.lastname: Butlin
authors.forename: Todd M
authors.initials: TM
authors.lastname: Corneillie
authors.forename: Claude F
authors.initials: CF
authors.lastname: Meares
mesh_terms: D000345:Affinity Labels; D002614:Chelating Agents / Q000737:chemistry; D002846:Chromatography, Affinity; D002851:Chromatography, High Pressure Liquid; D004602:Elements; D008401:Gas Chromatography-Mass Spectrometry; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry*; D006868:Hydrolysis; D007202:Indicators and Reagents; D013058:Mass Spectrometry; D008674:Metals, Rare Earth / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D011506:Proteins / Q000737:chemistry*; D013725:Terbium / Q000737:chemistry; D014357:Trypsin; D015019:Yttrium / Q000737:chemistry
chemical_list: D000345:Affinity Labels; D002614:Chelating Agents; D004602:Elements; D006573:Heterocyclic Compounds, 1-Ring; D007202:Indicators and Reagents; D008674:Metals, Rare Earth; D009942:Organometallic Compounds; D010455:Peptides; D011506:Proteins; D013725:Terbium; D015019:Yttrium; D014357:Trypsin