A glycine zipper motif mediates the formation of toxic β-amyloid oligomers in vitro and in vivo

Virginia Fonte,Gretchen H Stein,Michael A Silverman,Pascale Lacor,Emily Y Fan,Christopher D Link,Patrick Gonzales,Vishantie Dostal,Christine M Roberts,Natalie Dingwell,Jordi Magrane

doi:10.1186/1750-1326-6-61

Abstract

BackgroundThe β-amyloid peptide (Aβ) contains a Gly-XXX-Gly-XXX-Gly motif in its C-terminal region that has been proposed to form a "glycine zipper" that drives the formation of toxic Aβ oligomers. We have tested this hypothesis by examining the toxicity of Aβ variants containing substitutions in this motif using a neuronal cell line, primary neurons, and a transgenic C. elegans model.ResultsWe found that a Gly37Leu substitution dramatically reduced Aβ toxicity in all models tested, as measured by cell dysfunction, cell death, synaptic alteration, or tau phosphorylation. We also demonstrated in multiple models that Aβ Gly37Leu is actually anti-toxic, thereby supporting the hypothesis that interference with glycine zipper formation blocks assembly of toxic Aβ oligomers. To test this model rigorously, we engineered second site substitutions in Aβ predicted by the glycine zipper model to compensate for the Gly37Leu substitution and expressed these in C. elegans. We show that these second site substitutions restore in vivo Aβtoxicity, further supporting the glycine zipper model.ConclusionsOur structure/function studies support the view that the glycine zipper motif present in the C-terminal portion of Aβ plays an important role in the formation of toxic Aβ oligomers. Compounds designed to interfere specifically with formation of the glycine zipper could have therapeutic potential.

Highlights

Introduction of second site mutations intoAb G37L resulted in enhanced toxicity
To support the idea that the glycine zipper motif of Ab drives the formation of membrane pores, Kim et al demonstrated that Gly-to-Leu substitutions in this motif could block Ab pore formation in synthetic membranes and reduce Ab toxicity in cultured Neuro 2a neuroblastoma cells
Ab42 G37L is less toxic than wild type Ab in vivo We have previously described and characterized a transgenic C. elegans model in which induction of human Ab42 expression leads to intracellular accumulation of Ab in body wall muscle cells, resulting in a highly reproducible paralysis phenotype [5,18]

Summary

Introduction

Introduction of second site mutations intoAb G37L resulted in enhanced toxicity. This compensatory interaction is most striking in the N27G G37L variant, which is clearly more toxic than either single substitution (see Additional file 1 Figure S2). The b-amyloid peptide (Ab) contains a Gly-XXX-Gly-XXX-Gly motif in its C-terminal region that has been proposed to form a “glycine zipper” that drives the formation of toxic Ab oligomers We have tested this hypothesis by examining the toxicity of Ab variants containing substitutions in this motif using a neuronal cell line, primary neurons, and a transgenic C. elegans model. The hydrophobic C-terminal region of Ab (corresponding to the transmembrane portion of the amyloid precursor protein, APP) contains a Gly-XXX-Gly-XXX-Gly motif, termed a “glycine zipper” by Kim et al [13] These researchers pointed out that this motif is present in the transmembrane domains of a number of bacterial channel proteins, and structural modeling of these channel proteins suggests that the glycine zipper motif can drive the packing of transmembrane a-helices. These studies did not directly demonstrate that the G37L substitution disrupted the formation of Ab oligomers, or that oligomer disruption was the basis for the reduced toxicity in cell culture

Methods

Results

Conclusion