Identification of AL proteins from 10 λ-AL amyloidosis patients by mass spectrometry extracted from abdominal fat and heart tissue.

Background: Systemic AL amyloidosis arises from the misfolding of patient-specific immunoglobulin light chains (LCs). Potential drivers of LC amyloid formation are mutational changes and post-translational modifications (PTMs). However, little information is available on the exact primary structure of the AL proteins and their precursor LCs.

Objective: We analyse the exact primary structure of AL proteins extracted from 10 λ AL amyloidosis patients and their corresponding precursor LCs.

Materials and methods: By cDNA sequencing of the precursor LC genes in combination with mass spectrometry of the AL proteins, the exact primary structure and PTMs were determined. This information was used to analyse their biochemical properties.

Results: All AL proteins comprise the V_L and a small part of the C_L with a common C-terminal truncation region. While all AL proteins retain the conserved native disulphide bond of the V_L, we found no evidence for presence of other common PTMs. The analysis of the biochemical properties revealed that the isoelectric point of the V_L is significantly increased due to introduced mutations.

Conclusion: Our data imply that mutational changes influence the surface charge properties of the V_L and that common proteolytic processes are involved in the generation of the cleavage sites of AL proteins.