title: Role of electrostatic interactions in amyloid beta-protein (A beta) oligomer formation: a discrete molecular dynamics study.
abstract: Pathological folding and oligomer formation of the amyloid beta-protein (A beta) are widely perceived as central to Alzheimer's disease. Experimental approaches to study A beta self-assembly provide limited information because most relevant aggregates are quasi-stable and inhomogeneous. We apply a discrete molecular dynamics approach combined with a four-bead protein model to study oligomer formation of A beta. We address the differences between the two most common A beta alloforms, A beta 40 and A beta 42, which oligomerize differently in vitro. Our previous study showed that, despite simplifications, our discrete molecular dynamics approach accounts for the experimentally observed differences between A beta 40 and A beta 42 and yields structural predictions amenable to in vitro testing. Here we study how the presence of electrostatic interactions (EIs) between pairs of charged amino acids affects A beta 40 and A beta 42 oligomer formation. Our results indicate that EIs promote formation of larger oligomers in both A beta 40 and A beta 42. Both A beta 40 and A beta 42 display a peak at trimers/tetramers, but A beta 42 displays additional peaks at nonamers and tetradecamers. EIs thus shift the oligomer size distributions to larger oligomers. Nonetheless, the A beta 40 size distribution remains unimodal, whereas the A beta 42 distribution is trimodal, as observed experimentally. We show that structural differences between A beta 40 and A beta 42 that already appear in the monomer folding, are not affected by EIs. A beta 42 folded structure is characterized by a turn in the C-terminus that is not present in A beta 40. We show that the same C-terminal region is also responsible for the strongest intermolecular contacts in A beta 42 pentamers and larger oligomers. Our results suggest that this C-terminal region plays a key role in the formation of A beta 42 oligomers and the relative importance of this region increases in the presence of EIs. These results suggest that inhibitors targeting the C-terminal region of A beta 42 oligomers may be able to prevent oligomer formation or structurally modify the assemblies to reduce their toxicity.
authors.affiliation: Center for Polymer Studies, Department of Physics, Boston University, Boston, Massachusetts, USA.
authors.forename: Sijung
authors.initials: S
authors.lastname: Yun
authors.forename: B
authors.initials: B
authors.lastname: Urbanc
authors.forename: L
authors.initials: L
authors.lastname: Cruz
authors.forename: G
authors.initials: G
authors.lastname: Bitan
authors.forename: D B
authors.initials: DB
authors.lastname: Teplow
authors.forename: H E
authors.initials: HE
authors.lastname: Stanley
mesh_terms: D016229:Amyloid beta-Peptides / Q000737:chemistry* / Q000378:metabolism*; D003198:Computer Simulation; D019281:Dimerization; D008956:Models, Chemical; D055672:Static Electricity
chemical_list: D016229:Amyloid beta-Peptides