N-(L-isoaspartyl)-L-cysteine (S)-2-amino-4-((R)-1-carboxy-2-sulfanylethyl)amino-4-oxobutanoic acid -17.026548385620117188 -17.030000686645507812 2-(3-amino-3-carboxypropanoyl)amino-3-mercaptopropanoic acid 2-amino-N4-(1-carboxy-2-mercaptoethyl)butanediamic acid 201.03338623046875 201.220001220703125 A protein modification that effectively crosslinks L-aspartic acid and L-cysteine residues via an isopeptide bond to form N-(L-isoaspartyl)-L-cysteine. C 0 H -3 N -1 O 0 S 0 C 7 H 9 N 2 O 3 S 1 C, N CROSSLNK Isoaspartyl cysteine isopeptide (Cys-Asn) Cross-link 2. MOD:00221 N-(L-isoaspartyl)-L-cysteine N-beta-aspartylcysteine N-isoaspartyl cysteine N-term PSI-MOD natural uniprot.ptm:PTM-0151 isopeptide crosslinked residues crosslinked residues with loss of ammonia crosslinked L-asparagine residue crosslinked L-cysteine residue