One of the main applications of protein sequencing (or primary, de novo, amino acid sequencing) is to fulfil an important biosimilar regulatory requirement. Primary amino acid sequencing is an essential analysis during the development of a biosimilar, because you must ensure that the primary protein sequence of the biosimilar is identical to that of the innovator product. This is the only way to prove that the biosimilar is the same molecule as the target (or innovator/ reference) molecule. It is not sufficient to draw conclusions about the amino acid sequence based on peptide mapping or the DNA sequence (due to transcription or translation errors).
Once the protein sequences of the biosimilar and innovator are proven to be identical, other comparability studies should be performed to show that the molecules are similar in their functionality and their secondary, tertiary and higher order structure.