title: Millisecond radiolytic modification of peptides by synchrotron X-rays identified by mass spectrometry.
abstract: Radiolysis of peptide and protein solutions with high-energy X-ray beams induces stable, covalent modifications of amino acid residues that are useful for synchrotron protein footprinting. A series of 5-14 amino acid residue peptides of varied sequences were selected to study their synchrotron radiolysis chemistry. Radiolyzed peptide products were detected within 10 ms of exposure to a white light synchrotron X-ray beam. Mass spectrometry techniques were used to characterize radiolytic modification to amino acids cysteine (Cys), methionine (Met), phenylalanine (Phe), tyrosine (Tyr), tryptophan (Trp), proline (Pro), histidine (His), and leucine (Leu). A reactivity order of Cys, Met >> Phe, Tyr, > Trp > Pro > His, Leu was determined under aerobic reaction conditions from MS/MS analysis of the radiolyzed peptide products. Radiolysis of peptides in 18O-labeled water under aerobic conditions revealed that oxygenated radical species from air and water both contribute to the modification of amino acid side chains. Cysteine and methionine side chains reacted with hydroxyl radicals generated from radiolysis of water as well as molecular oxygen. Phenylalanine and tyrosine residues were modified predominantly by hydroxyl radicals, and the source of modification of proline was exclusively through molecular oxygen.
authors.affiliation: Albert Einstein Center for Synchrotron BioSciences, Department of Physiology & Biophysics, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461, USA. maleknia@aecom.yu.edu
authors.forename: S D
authors.initials: SD
authors.lastname: Maleknia
authors.forename: M
authors.initials: M
authors.lastname: Brenowitz
authors.forename: M R
authors.initials: MR
authors.lastname: Chance
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis / Q000737:chemistry; D008024:Ligands; D013058:Mass Spectrometry / Q000379:methods; D010455:Peptides / Q000032:analysis / Q000737:chemistry* / Q000528:radiation effects*; D017510:Protein Folding; D017356:Synchrotrons; D014965:X-Rays
chemical_list: D000596:Amino Acids; D008024:Ligands; D010455:Peptides