Dissection of the amyloid formation pathway in AL amyloidosis

Pamina Kazman,Harald Engelhardt,Johannes Buchner,Ramona M Absmeier

doi:10.1038/s41467-021-26845-0

Pamina Kazman, Harald Engelhardt + Show 2 more

Open Access

https://doi.org/10.1038/s41467-021-26845-0

Copy DOI

Abstract

In antibody light chain (AL) amyloidosis, overproduced light chain (LC) fragments accumulate as fibrils in organs and tissues of patients. In vitro, AL fibril formation is a slow process, characterized by a pronounced lag phase. The events occurring during this lag phase are largely unknown. We have dissected the lag phase of a patient-derived LC truncation and identified structural transitions that precede fibril formation. The process starts with partial unfolding of the VL domain and the formation of small amounts of dimers. This is a prerequisite for the formation of an ensemble of oligomers, which are the precursors of fibrils. During oligomerization, the hydrophobic core of the LC domain rearranges which leads to changes in solvent accessibility and rigidity. Structural transitions from an anti-parallel to a parallel β-sheet secondary structure occur in the oligomers prior to amyloid formation. Together, our results reveal a rate-limiting multi-step mechanism of structural transitions prior to fibril formation in AL amyloidosis, which offers, in the long run, opportunities for therapeutic intervention.

Highlights

In antibody light chain (AL) amyloidosis, overproduced light chain (LC) fragments accumulate as fibrils in organs and tissues of patients
For a better understanding of AL amyloidosis, we set out to resolve the molecular mechanism of structural changes occurring during the lag phase for the well-characterized patient LC truncation Pat-1 that represents the major component of the deposited fibrils
To obtain insights into the molecular events occurring during the lag phase, we first monitored changes in the solubility of the variable domain (VL) domain under conditions favoring rapid fibril formation (37 °C, shaking at 750 rpm, 0.5 mM SDS)

Summary

Introduction

In antibody light chain (AL) amyloidosis, overproduced light chain (LC) fragments accumulate as fibrils in organs and tissues of patients. We have dissected the lag phase of a patient-derived LC truncation and identified structural transitions that precede fibril formation. The hallmark of AL amyloidosis is the transformation of soluble monomeric protein into insoluble amyloid fibrils[12,13] Their presence correlates strongly with the disease and the impairment of organs in which they are deposited. Oligomeric intermediates of the amyloidogenic proteins and a nucleated polymerization mechanism have been suggested[16,19,20,21,22]. In AL amyloidosis, the presence of oligomers forming during the lag phase and the accompanied structural transitions prior to amyloid formation have not been investigated so far. We elucidated the processes taking place during the lag phase prior to fibril formation of the well-studied pathogenic VL domain Pat-16. We identified intermediate oligomeric species on the fibril pathway and associated structural rearrangements using a broad range of biophysical analyses

Methods

Results

Conclusion