Identification and characterization of an IgG sequence variant with an 11 kDa heavy chain C-terminal extension using a combination of mass spectrometry and high-throughput sequencing analysis.

Protein primary structure is a potential critical quality attribute for biotherapeutics. Identifying and characterizing any sequence variants present is essential for product development. A sequence variant ~11 kDa larger than the expected IgG mass was observed by size-exclusion chromatography and two-dimensional liquid chromatography coupled with online mass spectrometry.