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 two ex vivo fibril structures of a λ3 LC. The fibrils were extracted from the explanted heart of a patient (FOR005) and consist of 115-residue fibril proteins, 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.

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

“…PAR or PAIN type experiments ( 52 , 53 ). Very recently, the AL-fibril structure obtained from patient tissue has been solved using cryo-EM ( 54 ). There, fibrils have been extracted from heart tissue and analyzed after purification.…”

Protease Resistance of ex vivo Amyloid Fibrils implies the proteolytic Selection of disease-associated Fibril Morphologies

“…1); that is, their fibrils consist of full-length TTR as well as TTR fragments [28]. AL amyloid fibrils were purified from explanted hearts of patients FOR001, FOR005 [14] and FOR006 [29] with λ-AL amyloidosis and severe cardiomyopathy. Cases FOR001 and FOR006 are associated with a λ1 LC, FOR006 with a λ3 LC.…”

Challenges in sample preparation and structure determination of amyloids by cryo-EM

“…While it was assumed that monomer structure can change within one fibril, it was recently described by Radamaker et al. ( 49 ) that these structural switches can occur multiple times within one fibril. These findings add even more complexity to the topic of amyloid fibril polymorphism.…”

“…2 A ) are usually determined manually, for example, from 2D classes ( 154 ) or micrographs. Interestingly, two different monomer folds, which were observed within one fibril polymorph, could be separated in 3D classification for a sample from amyloid light-chain amyloidosis ( 49 ). However, the separation of different morphologies by hand is a laborious and error-prone task.…”