Beta-amyloid peptide (Ab), the primary protein component of senile plaques in AIzheimer's disease (AD), plays an important role in neurotoxicity. Peptide structure and aggregation state are important in toxicity. However, the exact structure of the toxic form of the peptide and the mechanism by which it interacts with a cell to cause toxicity are unknown. ? ? Based on our preliminary results, we hypothesize that one or more intermediate sized oligomers of Ab (smaller than a fibril) interact with cells via a membrane interaction that leads to toxicity; that this interaction with the membrane will involve specific residues on the surface of the Ab oligomer (and that those residues involved in the interaction will be the same, regardless of the size of Ab oligomer interacting with the membrane); and that cell toxicity can be prevented by preventing the Ab-membrane interaction, either by altering peptide residues involved in the peptide membrane interaction, or by altering membrane components involved in the interaction. ? ? To test our hypothesis, we will use a variety of methods to fractionate Ab and/or prepare Ab with different degrees of oligomerization/aggregation. We will develop a rapid method for assessment of Ab peptide biological activity (based on Ab-induced GTPase activity) that leads to toxicity. We will use hydrogen exchange followed by mass spectrometry (HX-MS) to characterize the exposed surfaces of oligomers associated with biological activity and to determine which regions of the peptide are buried in the membrane during peptide-membrane interactions. Finally, we will address the biological relevance of the interactions examined by determining if inhibition of those interactions via chemical modification of residue substitution results in attenuated GTPase activity or toxicity. If our hypothesis, in its entirety is correct, insights gained from these investigations will provide the basis for the design of agents that interfere directly with Ab-membrane interactions and prevent toxicity. If, however, only a portion of our hypothesis is correct, we will, at the least, have developed new tools with which to investigate Ab-self and Ab-membrane interactions associated with toxicity. ? ?
