Molecular mechanism of amyloidogenic mutations in hypervariable regions of antibody light chains

Abstract

Systemic light chain (AL) amyloidosis is a fatal protein misfolding disease in which excessive secretion, misfolding, and subsequent aggregation of free antibody light chains eventually lead to deposition of amyloid plaques in various organs. Patient-specific mutations in the antibody V L domain are closely linked to the disease, but the molecular mechanisms by which certain mutations induce misfolding and amyloid aggregation of antibody domains are still poorly understood. Here, we compare a patient V L domain with its nonamyloidogenic germline counterpart and show that, out of the five mutations present, two of them strongly destabilize the protein and induce amyloid fibril formation. Surprisingly, the decisive, disease-causing mutations are located in the highly variable complementarity determining regions (CDRs) but exhibit a strong impact on the dynamics of conserved core regions of the patient V L domain. This effect seems to be based on a deviation from the canonical CDR structures of CDR2 and CDR3 induced by the substitutions. The amyloid-driving mutations are not necessarily involved in propagating fibril formation by providing specific side chain interactions within the fibril structure. Rather, they destabilize the V L domain in a specific way, increasing the dynamics of framework regions, which can then change their conformation to form the fibril core. These findings reveal unexpected influences of CDR-framework interactions on antibody architecture, stability, and amyloid propensity.

The AL Amyloid Fibril: Looking for a Link between Fibril Formation and Structure

“…Changes in primary structure introduced by somatic hypermutation into the germline sequence or by posttranslational modifications are also discussed as drivers of light chain aggregation [8,17]. The identification of critical amino acid positions and their concentration in specific secondary structure regions showed that the location and nature of the mutation, rather than the number, determines the amyloidogenicity of light chains [18][19][20][21][22]. Some mutations have been attributed to a decrease in thermodynamic stability [18,[23][24][25], increase in conformational dynamics [17,20,21] or effects on interdomain interactions [26,27].…”

MALDI mass spectrometry imaging unravels organ and amyloid‐type specific peptide signatures in pulmonary and gastrointestinal amyloidosis

“…The recombinant light chain FOR005 refers to the light chain of an ALλ amyloidosis case with cardiac involvement. Recombinant light chain FOR005 was expressed and purified as previously described [29]. Briefly, the DNA plasmid (pET28b) encoding for FOR005 light chain was transformed into Escherichia coli BL21 (DE3)‐star cells and the protein was expressed as insoluble inclusion bodies over night at 37°C using 1 mmol/L isopropyl β‐D‐1‐thiogalactopyranosid for induction.…”

Genetic pathogenesis of immunoglobulin light chain amyloidosis: basic characteristics and clinical applications

“…Somatic mutations in the IgL genes, generated in the process of immunoglobulin synthesis, add complexity to the IgL structure. The burden of the somatic mutations and the specific site that a mutation occurs can influence the stability and amyloidogenicity of IgL [91][92][93][94][95]. A model from a recent study based on somatic mutations in IgL displays high sensitivity and specificity to predict the free light chain toxicity [96].…”