Table I. Proteolytic Ab peptides containing lysine residues cross-linked by TG2
Target LysaSequenceMass (Da)bRegion
IgG1
 235SCDKTH1468.7Hinge
 235SCDKTHTCPPCPAPELL2704.2Hinge
IgG3
 241E / 241T / 241IICPEPKSCDTPPPCPR2502.3/2519.4Hinge
 353ALPAPIEKTISK1989.2CH2
IgD
 241ZGGEEKK1368.8Hinge
 241Z /241AAGGEEKKK1496.9Hinge
 241AA/241BBKKEK1253.8Hinge
 241BBKEK1125.7Hinge
 282VVGSDLKDAHLTW2162.3CH2
 367ALREPAAQAPVKL2086.3CH3
  • Target lysines are shown in bold. In the cases where two lysines were juxtaposed, only one was cross-linked, but the two could not be distinguished. In one peptide, a glutamine residue was found to be deamidated by TG2 (underlined). The identified IgG3 hinge peptide was detected in two forms: with a free N terminus (2519.4 Da) and as a lactam (2502.3 Da), which was produced by spontaneous cyclization, resulting in the loss of ammonia.

  • a Lysine residues are numbered according to the Kabat numbering scheme (26).

  • b Masses include biotin–QLPR peptide cross-linked to TG2-targeted lysine residues (+722.5 Da) and iodoacetamide modifications of cysteines (+57 Da).