Journal of The American Society for Mass Spectrometry

, Volume 24, Issue 11, pp 1710–1721

Chemical Derivatization of Peptide Carboxyl Groups for Highly Efficient Electron Transfer Dissociation

  • Brian L. Frey
  • Daniel T. Ladror
  • Samuel B. Sondalle
  • Casey J. Krusemark
  • April L. Jue
  • Joshua J. Coon
  • Lloyd M. Smith
Focus: Electron Transfer Dissociation: Research Article

DOI: 10.1007/s13361-013-0701-2

Cite this article as:
Frey, B.L., Ladror, D.T., Sondalle, S.B. et al. J. Am. Soc. Mass Spectrom. (2013) 24: 1710. doi:10.1007/s13361-013-0701-2

Abstract

The carboxyl groups of tryptic peptides were derivatized with a tertiary or quaternary amine labeling reagent to generate more highly charged peptide ions that fragment efficiently by electron transfer dissociation (ETD). All peptide carboxyl groups—aspartic and glutamic acid side-chains as well as C-termini—were derivatized with an average reaction efficiency of 99 %. This nearly complete labeling avoids making complex peptide mixtures even more complex because of partially-labeled products, and it allows the use of static modifications during database searching. Alkyl tertiary amines were found to be the optimal labeling reagent among the four types tested. Charge states are substantially higher for derivatized peptides: a modified tryptic digest of bovine serum albumin (BSA) generates ~90% of its precursor ions with z  >  2, compared with less than 40 % for the unmodified sample. The increased charge density of modified peptide ions yields highly efficient ETD fragmentation, leading to many additional peptide identifications and higher sequence coverage (e.g., 70 % for modified versus only 43 % for unmodified BSA). The utility of this labeling strategy was demonstrated on a tryptic digest of ribosomal proteins isolated from yeast cells. Peptide derivatization of this sample produced an increase in the number of identified proteins, a >50 % increase in the sequence coverage of these proteins, and a doubling of the number of peptide spectral matches. This carboxyl derivatization strategy greatly improves proteome coverage obtained from ETD-MS/MS of tryptic digests, and we anticipate that it will also enhance identification and localization of post-translational modifications.

Key words

Peptide derivatization Peptide carboxylic acids Carboxyl group derivatization Fixed charge modification Tertiary amine Charge state Peptide fragmentation Electron transfer dissociation Amino acid sequence Sequence coverage Ribosomal protein Proteomics Mass spectrometry 

Copyright information

© American Society for Mass Spectrometry 2013

Authors and Affiliations

  • Brian L. Frey
    • 1
  • Daniel T. Ladror
    • 1
  • Samuel B. Sondalle
    • 1
  • Casey J. Krusemark
    • 1
  • April L. Jue
    • 1
  • Joshua J. Coon
    • 1
    • 2
    • 3
  • Lloyd M. Smith
    • 1
    • 3
  1. 1.Department of ChemistryUniversity of Wisconsin-MadisonMadisonUSA
  2. 2.Department of Biomolecular ChemistryUniversity of Wisconsin-MadisonMadisonUSA
  3. 3.Genome Center of WisconsinUniversity of Wisconsin-MadisonMadisonUSA

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