title: Isoaspartate in peptides and proteins: formation, significance, and analysis.
abstract: Formation of isoaspartyl peptide bonds (isoAsp) is one of the most common forms of non-enzymatic degradation of peptides and proteins under mild conditions. IsoAsp arises when certain Asn-Xaa and Asp-Xaa sites undergo a spontaneous intramolecular rearrangement to form a succinimide which subsequently hydrolyzes to generate a mixture of isoAsp-Xaa and Asp-Xaa linkages in a ratio of approximately 2:1. This pathway is responsible for the much greater susceptibility of asparagine, compared with glutamine, to deamidation at neutral and alkaline pH. Rearrangement occurs most readily at Asn-Gly, Asn-Ser, and Asp-Gly sequences where the local polypeptide chain flexibility is high. Formation of isoAsp can decrease the biological activity of a protein pharmaceutical, alter its susceptibility to proteolytic degradation, and elicit autoimmunity. The enzyme protein L-isoaspartyl methyltransferase can be used to measure isoAsp sites in the low pmol range with or without the use of radioisotopes.
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine 92697-3900, USA. dwaswad@uci.edu
authors.forename: D W
authors.initials: DW
authors.lastname: Aswad
authors.forename: M V
authors.initials: MV
authors.lastname: Paranandi
authors.forename: B T
authors.initials: BT
authors.lastname: Schurter
mesh_terms: D001224:Aspartic Acid / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D007536:Isomerism; D010455:Peptides / Q000737:chemistry*; D011506:Proteins / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry; D010959:Tissue Plasminogen Activator / Q000737:chemistry
chemical_list: D010455:Peptides; D011506:Proteins; D011994:Recombinant Proteins; D001224:Aspartic Acid; D010959:Tissue Plasminogen Activator