Surface-catalyzed Amyloid Fibril Formation

Min Zhu,Pierre O Souillac,Cristian Ionescu-Zanetti,Sue A Carter,Anthony L Fink

doi:10.1074/jbc.m207225200

Min Zhu, Pierre O Souillac + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m207225200

Copy DOI

Abstract

Light chain (or AL) amyloidosis is characterized by the pathological deposition of insoluble fibrils of immunoglobulin light chain fragments in various tissues, walls of blood vessels, and basement membranes. In the present investigation, the in vitro assembly of a recombinant amyloidogenic light chain variable domain, SMA, on various surfaces was monitored using atomic force microscopy. SMA formed fibrils on native mica at pH 5.0, conditions under which predominantly amorphous aggregates form in solution. Fibril formation was accelerated significantly on surfaces compared with solution; for example, fibrils grew on surfaces at significantly faster rates and at much lower concentrations than in solution. No fibrils were observed on hydrophobic or positively charged surfaces or at pH >7.0. Two novel types of fibril growth were observed on the surface: bidirectional linear assembly of oligomeric units, and linear growth from preformed amorphous cores. In addition to catalyzing the rate of fibrillation, the mechanism of fibril formation on the surfaces was significantly different from in solution, but it may be more physiologically relevant because in vivo the deposits are associated with surfaces.

Highlights

Immunoglobin (Ig) light chains (LCs)1 are involved in various protein deposition diseases, such as AL amyloidosis, LC deposition disease, myeloma cast nephropathy, and acquired Fanconi’s syndrome [1,2,3,4]
To investigate the potential role of surfaces in amyloid fibril formation we incubated small pieces of mica in solutions of SMA, typically under conditions where fibrils were not formed over a time period of a week or longer in bulk solution
The results reported here indicate that surfaces can catalyze the formation of amyloid fibrils and that the mechanism of surface-induced fibrillation may be significantly different from that occurring in bulk solution

Summary

Introduction

Immunoglobin (Ig) light chains (LCs) are involved in various protein deposition diseases, such as AL amyloidosis ( known as primary systemic amyloidosis or LC amyloidosis), LC deposition disease, myeloma cast nephropathy, and acquired Fanconi’s syndrome [1,2,3,4]. Because LCs are frequently found to deposit in arterial walls and basement membranes [2], interfacial phenomena and the interaction between protein and the surface may be involved in the aggregation process. More than 18 different amyloidogenic proteins or peptides have been identified which are associated with protein deposition disease These proteins share similar morphology of fibrils (18 –21), all forming twisted, linear, Congo Red-binding fibrils, typically 5–10 nm in diameter with a crossed ␤-pleated sheet conformation. We have observed that the in vitro fibril formation of SMA is sensitive to the test tube materials and the nature of the beads used for stirring This can be explained by surface interactions and subsequent conformation changes caused by the attachment of the protein to the surface. We have monitored the fibril assembly of the Ig LC SMA in solution by AFM, and a model for fibril formation involving a hierarchical assembly process from protofilaments

Methods

Results

Conclusion