Epitope Mapping by NMR of a Novel Anti-A\u03b2 Antibody (STAB-MAb)

Adrián Posado-Fernández,Orfeu Flores,Gonçalo Dória,Eurico J Cabrita,Cláudia F Afonso

doi:10.1038/s41598-019-47626-2

Abstract

Alzheimer´s Disease (AD) is one of the most common neurodegenerative disorders worldwide. Excess of β-amyloid (Aβ), a peptide with a high propensity to misfold and self-aggregate, is believed to be the major contributor to the observed neuronal degeneration and cognitive decline in AD. Here, we characterize the epitope of a novel anti-Aβ monoclonal antibody, the STAB-MAb, which has previously demonstrated picomolar affinities for both monomers (KD = 80 pM) and fibrils (KD = 130 pM) of Aβ(1–42) and has shown therapeutic efficacy in preclinical mouse models of AD. Our findings reveal a widespread epitope that embraces several key Aβ residues that have been previously described as important in the Aβ fibrillation process. Of note, STAB-MAb exhibits a stronger affinity for the N-terminus of Aβ and stabilizes an α-helix conformation in the central to N-terminal region of the peptide, in addition to disrupting a characteristic salt-bridge of a hairpin structure present in fibrils. The NMR derived epitope supports the observed results from ThT-monitored fluorescence and electron microscopy experiments, in which STAB-MAb was shown to inhibit the formation of aggregates and promote disruption of pre-formed fibrils. In combination with the published in vitro and in vivo assays, our study highlights STAB-MAb as a rare and versatile antibody with analytical, diagnostic and therapeutic efficacy.

Highlights

One of the classical neuropathological hallmarks associated with Alzheimers Disease (AD) is the presence of extracellular senile plaques resulting from the accumulation of β-amyloid (Aβ) peptides
The aggregation kinetics of Aβ in the presence of STAB-Mab were monitored by the Thioflavin T (ThT) assay
We demonstrated that STAB-MAb can completely inhibit the formation of fibril structures when present at a 1:1 molar concentration with Aβ

Summary

Introduction

One of the classical neuropathological hallmarks associated with AD is the presence of extracellular senile plaques resulting from the accumulation of β-amyloid (Aβ) peptides. These insoluble deposits of Aβ are derived from the proteolytic cleavage of a larger membrane protein, named the amyloid precursor protein (APP), following its sequential processing by β- and γ-secretases in neurons[4,5]. Initial studies on the solution structure of amyloid peptides have shown that in aqueous environments, Aβ(1–28) is essentially a random coil, while Aβ(1–39) adopts both random coil and β-sheet structures in equal www.nature.com/scientificreports/.

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