isopeptide crosslinked residues N-(L-isoaspartyl)-glycine (2S)-2-amino-4-(carboxymethyl)amino-4-oxobutanoic acid 155.0456695556640625 155.1300048828125 2-amino-N4-(carboxymethyl)-butanediamic acid A protein modification that effectively crosslinks either an L-asparagine residue or an L-aspartic acid residue with a glycine residue by an isopeptide bond with formation of N-(L-isoaspartyl)glycine. C 6 H 7 N 2 O 3 Cross-link 2. G MOD:01928 N-(L-isoaspartyl)-glycine N-beta-aspartylglycine N-term N4-(carboxymethyl)-asparagine PSI-MOD XLNK-4Asp-NGly isoaspartyl glycine natural crosslinked glycine residue