Mass spectrometric characterization of amyloidogenic immunoglobulin light chains from patients with primary amyloidosis

Primary amyloidosis, also known as amyloid light chain amyloidosis (AL), is a protein misfolding disease associated with the overproduction of immunoglobulin (Ig) light chains by a monoclonal population of bone marrow plasma cells. The amyloid deposits are composed mainly of the intact or truncated monoclonal Ig light chains that self-assemble into long unbranched fibrils with a beta-pleated sheet structure. The population of state(s) that have been partially unfolded via destabilization of the native protein conformation has become recognized as an essential event in the fibril growth process and amyloidogenic pathology. While previous studies have indicated that amino acid substitutions in the variable domains of light chains could facilitate fibril formation by impairing their folding stability, the influence of other structural features such as post-translational modifications (PTMs) remains to be further explored.;This thesis focuses on the de novo determination of the cDNA derived amino acid sequences and the characterization of PTMs of four patient-derived amyloidogenic light chains (AL-00051 kappa IV, AL-01140 kappa III, AL-98002 kappa I, and AL-01029 lambda VI) by various mass spectrometry (MS)-based approaches involving multiple enzyme digestions, chemical and enzymatic derivatizations, and different tandem MS analyses such as collision-induced dissociation (CID), electron capture dissociation (ECD), and infrared multiphoton dissociation (IRMPD). A wide variety of PTMs were identified in these amyloidogenic light chains, including N-terminal deamination and decarboxylation, N-terminal truncations and internal deletions, N-linked glycosylation, disulfide-linked dimerization, S-sulfonation, C-terminal sulfonamide and thiosulfonate linkages, asparagine deamidation, tryptophan oxidation, cyclization of glutamine, and formation of 3-chlorotyrosine. All or some of these modifications may contribute to the reduced folding stability of the light chains, and enhance the amyloidogenic properties of these proteins.