Glycoproteomic analysis of abnormal N-glycosylation on the kappa chain of cryocrystalglobulin in a patient of multiple myeloma

SUMMARY Crystalglobulinemia (cryocrystalglobulinemia) is a rare complication of multiple myeloma. Crystallization of immunoglobulin in blood circulation causes systemic vasculopathy especially in skin and kidney. We found a rare case of crystalglobulinemia in which the light chain was N-glycosylated. The abnormal N-glycosylation was primarily detected as the molecular mass shift on SDS-PAGE by PNGase F treatment. The cryocrystalglobulin was shown to be composed of 55-kDa heavy and 32-kDa light chains on SDS-PAGE. However, the apparent molecular masses of them shifted to 51 kDa and 28 kDa, respectively by PNGase-F treatment. The cryocrystalglobulin was identified as an IgG κ type by peptide mass fingerprinting. The N-glycans on the κ light chain were assigned to non-fucosylated biantennary oligosaccharides and their bisected forms by MALDI-TOF MS/MS analysis of glycopeptides. Sialylation of the abnormal N-glycans was suggested by linear-mode MS and confirmed by HPLC analysis. The N-glycosylation consensus Asn (Asn-Xxx-Ser/Thr) was found in the glycopeptide at the N-glycosylation site determined as “EIVMTQSPANLSVLPGER” by MALDI-TOF MS/MS, in which the consensus Asn (N) was converted to Asp (D) in the enzymatically deglycosylated peptide.