In the biopharmaceutical development of an antibody, it is known that heterogeneity may sometimes occur in the N-terminal or C-terminus of a protein. For example, there are cases where the terminal amino acid has been eliminated or modified, so it is very important to grasp such a change in structure to maintain the quality of biopharmaceuticals. Typically, when determining the amino acid sequence of a protein, a protein sequencer is used to determine the N-terminal amino acids one by one. If the N-terminal amino group (α-amino group) has been modified, the de-blocking method is typically used to enable the use of the protein sequencer. But, sometimes this de-blocking is not successful due to the existence of several types of modifications and the difficulty of optimizing the reaction conditions. Therefore, sequence analysis by mass spectrometry is sometimes required as an alternative.
Here, we introduce an example of N-terminal amino acid sequence analysis of antibody molecules using the Shimadzu MALDI-7090 high-resolution MALDI-TOF MS.