Chapter 16 Analysis of Deamidation in Proteins

Abstract

Publisher Summary Deamidation of asparagine (Asn) and glutamine (Gln) residues to their acidic counterparts is a common posttranslational modification (PTM) on proteins. Deamidation occurs nonenzymatically in solution and with the exception of –NP– and –QP– sequences; it occurs at all Asn and Gln residues in all proteins eventually. However, the rates vary dramatically with the primary and higher-order structure of proteins. Deamidation results in a charge change and a +0.984 Da mass shift, both of which are readily detectable by many methods, but it results in a mixture of isomers that are relatively difficult to differentiate. A recently introduced mass spectrometric (MS) method uses electron capture dissociation (ECD) fragmentation patterns to distinguish aspartyl and isoaspartyl residues formed from deamidation of Asn residues. The ECD method not only distinguishes the isomers but also suggests several methods to quantify them. One method that has been demonstrated in the cytochrome C case utilizes the characteristic 1:3 branching ratio on deamidation to provide a calibration point that allows relative quantitation.