Gas-phase fragmentation characteristics of benzyl-aminated lysyl-containing tryptic peptides.
The fragmentation characteristics of peptides derivatized at the side-chain epsilon-amino group of lysyl residues via reductive amination with benzaldehyde have been examined using collision-induced dissociation (CID) tandem mass spectrometry. The resulting MS/MS spectra exhibit peaks representing product ions formed from two independent fragmentation pathways. One pathway results in backbone fragmentation and commonly observed sequence ion peaks. The other pathway corresponds to the unsymmetrical, heterolytic cleavage of the C(zeta)-N(epsilon) bond that links the benzyl derivative to the side-chain lysyl residue. This results in the elimination of the derivative as a benzylic or tropylium carbocation and a (n - 1)(+)-charged peptide product (where n is the precursor ion charge state). The frequency of occurrence of the elimination pathway increases with increasing charge of the precursor ion. For the benzyl-modified tryptic peptides analyzed in this study, peaks representing products from both of these pathways are observed in the MS/MS spectra of doubly-charged precursor ions, but the carbocation elimination pathway occurs almost exclusively for triply-charged precursor ions. The experimental evidence presented herein, combined with molecular orbital calculations, suggests that the elimination pathway is a charge-directed reaction contingent upon protonation of the secondary epsilon-amino group of the benzyl-derivatized lysyl side chain. If the secondary epsilon-amine is protonated, the elimination of the carbocation is observed. If the precursor is not protonated at the secondary epsilon-amine, backbone fragmentation persists. The application of appropriately substituted benzyl analogs may allow for selective control over the relative abundance of product ions generated from the two pathways.
Simon
Eric S
ES
Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA. essimon@umich.edu
Papoulias
Panagiotis G
PG
Andrews
Philip C
PC
D000588:Amines / Q000737:chemistry; D001593:Benzyl Compounds / Q000737:chemistry*; D005740:Gases / Q000737:chemistry*; D008239:Lysine / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D044367:Phase Transition; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D053719:Tandem Mass Spectrometry / Q000379:methods; D014357:Trypsin / Q000737:chemistry*
D000588:Amines; D001593:Benzyl Compounds; D005740:Gases; D010455:Peptides; D014357:Trypsin; D008239:Lysine
Mass Spectrom Rev. 2005 Jul-Aug;24(4):508-48
15389847
Mass Spectrom Rev. 1998 Jul-Aug;17(4):255-74
10224676
Anal Chem. 1993 Jul 1;65(13):1703-8
8368523
Nature. 2003 Mar 13;422(6928):198-207
12634793
J Am Soc Mass Spectrom. 2005 Jul;16(7):1131-50
15923125
J Mass Spectrom. 2000 Dec;35(12):1399-406
11180630
Mol Cell Proteomics. 2007 Nov;6(11):1942-51
17673454
Chem Rev. 2001 Feb;101(2):269-95
11712248
J Mass Spectrom. 2003 Apr;38(4):373-7
12717748
J Proteome Res. 2005 Jan-Feb;4(1):101-8
15707364
J Am Soc Mass Spectrom. 2004 Feb;15(2):158-67
14766283
Proc Natl Acad Sci U S A. 2004 Jun 29;101(26):9528-33
15210983
J Am Soc Mass Spectrom. 2006 Dec;17(12):1631-42
16935522
Anal Chem. 2008 Dec 1;80(23):9279-87
19551991
J Proteome Res. 2006 Sep;5(9):2448-56
16944958
Rapid Commun Mass Spectrom. 2001;15(16):1457-72
11507760
J Am Soc Mass Spectrom. 2004 Jan;15(1):103-13
14698560
Mol Cell Proteomics. 2004 Dec;3(12):1154-69
15385600
J Mass Spectrom. 2009 Dec;44(12):1668-75
19824036
Biol Mass Spectrom. 1991 Jul;20(7):419-25
1932157
Anal Chem. 2003 Apr 1;75(7):156A-165A
12705581