Direct Mass Spectrometry-Based Detection and Antibody Sequencing of Monoclonal Gammopathy of Undetermined Significance from Patient Serum: A Case Study

Monoclonal gammopathyof undetermined significance (MGUS) is aplasma cell disorder characterized by the presence of a predominantmonoclonal antibody (i.e., M-protein) in serum, without clinical symptoms.Here we present a case study in which we detect MGUS by liquid-chromatographycoupled with mass spectrometry (LC-MS) profiling of IgG1 in humanserum. We detected a Fab-glycosylated M-protein and determined thefull heavy and light chain sequences by bottom-up proteomics techniquesusing multiple proteases, further validated by top-down LC-MS. Moreover,the composition and location of the Fab-glycan could be determinedin CDR1 of the heavy chain. The outlined approach adds to an expandingmass spectrometry-based toolkit to characterize monoclonal gammopathiessuch as MGUS and multiple myeloma, with fine molecular detail. Theability to detect monoclonal gammopathies and determine M-proteinsequences straight from blood samples by mass spectrometry providesnew opportunities to understand the molecular mechanisms of such diseases.