Nucleobindin 1 binds to multiple types of pre-fibrillar amyloid and inhibits fibrillization

Alessandra Bonito-Oliva,Thomas P Sakmar,Shahar Barbash,W Vallen Graham

doi:10.1038/srep42880

Abstract

During amyloid fibril formation, amyloidogenic polypeptides misfold and self assemble into soluble pre-fibrillar aggregates, i.e., protofibrils, which elongate and mature into insoluble fibrillar aggregates. An emerging class of chaperones, chaperone-like amyloid binding proteins (CLABPs), has been shown to interfere with aggregation of particular misfolded amyloid peptides or proteins. We have discovered that the calcium-binding protein nuclebindin-1 (NUCB1) is a novel CLABP. We show that NUCB1 inhibits aggregation of islet-amyloid polypeptide associated with type 2 diabetes mellitus, a-synuclein associated with Parkinson’s disease, transthyretin V30M mutant associated with familial amyloid polyneuropathy, and Aβ42 associated with Alzheimer’s disease by stabilizing their respective protofibril intermediates. Kinetic studies employing the modeling software AmyloFit show that NUCB1 affects both primary nucleation and secondary nucleation. We hypothesize that NUCB1 binds to the common cross-β-sheet structure of protofibril aggregates to “cap” and stabilize soluble macromolecular complexes. Transmission electron microscopy and atomic force microscopy were employed to characterize the size, shape and volume distribution of multiple sources of NUCB1-capped protofibrils. Interestingly, NUCB1 prevents Aβ42 protofibril toxicity in a cellular assay. NUCB1-stabilized amyloid protofibrils could be used as immunogens to prepare conformation-specific antibodies and as novel tools to develop screens for anti-protofibril diagnostics and therapeutics.

Highlights

During amyloid fibril formation, amyloidogenic polypeptides misfold and self assemble into soluble pre-fibrillar aggregates, i.e., protofibrils, which elongate and mature into insoluble fibrillar aggregates
Atomic Force Microscopy (AFM) experiments show that mutant variant of sNUCB1 (mtNUCB1) is present as both monomers and dimers with asymmetric and heterogeneous shape and height up to 1.4 nm (Supplementary Fig. S1)
In absence of mtNUCB1, the scaling exponent calculated across Aβ42 concentrations was −0.711, slightly higher than previous reports with recombinant Aβ4233 or depsipeptide- derived sources[39], and it remained relatively stable over the range of examined concentrations (Supplementary Fig. S2)

Summary

Introduction

During amyloid fibril formation, amyloidogenic polypeptides misfold and self assemble into soluble pre-fibrillar aggregates, i.e., protofibrils, which elongate and mature into insoluble fibrillar aggregates. Recent in vitro and in vivo studies have shown that molecular chaperones, or chaperone-like amyloid binding proteins (CLABPs), can efficiently inhibit amyloid formation and, might protect against amyloid-induced toxicity[24,25,26,27,28,29,30,31,32]. Their influence on the kinetics of amyloid aggregation intrinsically depends on the type of amyloid polypeptide and the specific inhibited step in the aggregation process. Whereas DNAJB6 prevents Aβaggregation by mainly acting on primary nucleation pathways[40], the molecular chaperone domain BRICHOS inhibits in vitro Aβaggregation by interfering potently and selectively with the secondary nucleation reaction[18,31,34,41]

Methods

Results

Conclusion