New example of proline-induced fragmentation in electrospray ionization mass spectrometry of peptides.
The positive ion electrospray ionization (ESI+) mass spectra of peptides usually display only protonated molecules provided that soft ionization conditions are applied (low cone voltage to prevent in-source dissociations). Such ions can be multiply charged depending on the molecular weight of the studied compounds. We have experienced an unexpected behavior during the ESI analysis of a modified peptide of relatively high mass (3079 Da). A specific fragmentation occurred even under soft energetic conditions, leading to a mass spectrum containing multiply charged molecular and fragment ions. The selective rupture involved the amide bond between the glutamic acid and proline residues (E-P sequence). The successive replacement of each amino acid by an alanine residue (positional scanning study) was undertaken to assess which part of the sequence induced such selective and abundant fragmentation on multiply charged species. The succession P-P was evidenced as the minimum unit giving rise to the first peptide bond rupture in the sequence X-P-P. Any acidic amino acid at the X position (X = D, E) favored the fragmentation by an intramolecular interaction. Such proline-induced fragmentation occurring readily in the source differed from the literature data on the specific behavior of proline-containing peptides where bond ruptures occur solely in dissociation conditions.
Maux
Delphine
D
CNRS-UMR 5810, Laboratoire des Aminoacides, Peptides et Protéines, Universités Montpellier I & II, Place E. Bataillon, 34095 Montpellier Cédex 05, France.
Enjalbal
Christine
C
Martinez
Jean
J
Aubagnac
Jean-Louis
JL
D000596:Amino Acids / Q000737:chemistry; D002138:Calibration; D008970:Molecular Weight; D010455:Peptides / Q000737:chemistry*; D011392:Proline / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013056:Spectrophotometry, Ultraviolet
D000596:Amino Acids; D010455:Peptides; D011392:Proline