title: Loss of internal backbone carbonyls: additional evidence for sequence-scrambling in collision-induced dissociation of y-type ions.
abstract: It is shown that y-type ions, after losing C-terminal H2O or NH3, can lose an internal backbone carbonyl (CO) from different peptide positions and yield structurally different product fragment ions upon collision-induced dissociation (CID). Such CO losses from internal peptide backbones of y-fragment ions are not unique to a single peptide and were observed in four of five model peptides studied herein. Experimental details on examples of CO losses from y-type fragment ions for an isotopically labeled AAAAHAA-NH2 heptapeptide and des-acetylated-α-melanocyte-stimulating hormone (dα-MSH) (SYSMEHFRWGKPV-NH2) are reported. Results from isotope labeling, tandem mass spectrometry (MS(n)), and ion mobility-mass spectrometry (IM-MS) confirm that CO losses from different amino acids of m/z-isolated y-type ions yield structurally different ions. It is shown that losses of internal backbone carbonyls (as CID products of m/z-isolated y-type ions) are among intermediate steps towards formation of rearranged or permutated product fragment ions. Possible mechanisms for generation of the observed sequence-scrambled a-"like" ions, as intermediates in sequence-scrambling pathways of y-type ions, are proposed and discussed.
authors: Institute of Biomedical Studies, Baylor University, Waco, TX, 76798, USA.
authors: Brett
authors: B
authors: Harper
authors: Mahsan
authors: M
authors: Miladi
authors: Touradj
authors: T
authors: Solouki
mesh_terms: D000595:Amino Acid Sequence; D007477:Ions / Q000737:chemistry; D013058:Mass Spectrometry / Q000379:methods*; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D007477:Ions; D010455:Peptides