Cryo-EM reveals structural breaks in a patient-derived amyloid fibril from systemic AL amyloidosis

Abstract

Systemic AL amyloidosis is a debilitating and potentially fatal disease that arises from the misfolding and fibrillation of immunoglobulin light chains (LCs). The disease is patient-specific with essentially each patient possessing a unique LC sequence. In this study, we present the first ex vivo fibril structures of a λ3 LC. The fibrils were extracted from the explanted heart of a patient (FOR005) and consist of 115 residues, mainly from the LC variable domain. The fibril structures imply that a 180° rotation around the disulfide bond and a major unfolding step are necessary for fibrils to form. The two fibril structures show highly similar fibril protein folds, differing in only a 12-residue segment. Remarkably, the two structures do not represent separate fibril morphologies, as they can co-exist at different z-axial positions within the same fibril. Our data imply the presence of structural breaks at the interface of the two structural forms.

AA amyloid fibrils from diseased tissue are structurally different from in vitro formed SAA fibrils

“…Several recent studies report structural differences between fibrils formed inside a test tube and fibrils extracted from diseased tissue [4][5][6][7][8] . Morphological differences depend, on the one hand, on the primary structure of the aggregating polypeptide chain and on the other hand on the conditions under which fibril formation occurs.…”

“…In vitro fibrils reproduce the generic structural features of amyloid fibrils, such as their linear morphology, cross-β structure and affinity for Congo red and thioflavin T dyes 3 , but an increasing number of recent studies found fibrils from patient tissue to be structurally different from in vitro fibrils from the same precursor protein. Examples hereof are the immunoglobulin light chain-derived fibrils in systemic AL amyloidosis 4,5 , the Aβ-derived fibrils in Alzheimer's disease 6 , tauderived fibrils in neurodegenerative diseases 7 , or the α-synucleinderived fibrils in multiple system atrophy 8 . Hence, out of the spectrum of fibril morphologies, that a polypeptide chain is able to adopt, only some morphologies are associated with disease, raising the question what might determine their pathological relevance?…”

Seeded fibrils of the germline variant of human λ-III immunoglobulin light chain FOR005 have a similar core as patient fibrils with reduced stability

“…Due to sensitivity issues, we were not able so far to collect a greater number of longrange distance restraints using e.g. PAR or PAIN type experiments (52,53). Very recently, the ALfibril structure obtained from patient tissue has been solved using cryo-EM (54).…”

Kinetic evidence for multiple aggregation pathways in antibody light chain variable domains

“…The nature of the proteolytic fragmentation that leads to loss of the variable domain is not fully understood, but proteomic experiments indicate that at least some cleavage occurs after deposition as amyloid (Lavatelli et al, 2020;Mazzini et al, 2022). High resolution structures of amyloid fibrils show that their cross-β core is formed from variable domain residues in nonnative conformations, with the disulfide bond intact but the orientation of the peptide chains around the disulfide reversed, relative to that in the native state (Radamaker et al, 2019(Radamaker et al, , 2021a(Radamaker et al, , 2021bSwuec et al, 2019). Unfolding of the native light chains is therefore required for amyloid formation.…”