Nanomedicine and protein misfolding diseases

Abstract

Misfolding and self assembly of proteins in nano-aggregates of different sizes and morphologies (nano-ensembles, primarily nanofilaments and nano-rings) is a complex phenomenon that can be facilitated, impeded, or prevented, by interactions with various intracellular metabolites, intracellular nanomachines controlling protein folding and interactions with other proteins. A fundamental understanding of molecular processes leading to misfolding and self-aggregation of proteins involved in various neurodegenerative diseases will provide critical information to help identify appropriate therapeutic routes to control these processes. An elevated propensity of misfolded protein conformation in solution to aggregate with the formation of various morphologies impedes the use of traditional physical chemical approaches for studies of misfolded conformations of proteins. In our recent alternative approach, the protein molecules were tethered to surfaces to prevent aggregation and AFM force spectroscopy was used to probe the interaction between protein molecules depending on their conformations. It was shown that formation of filamentous aggregates is facilitated at pH values corresponding to the maximum of rupture forces. In this paper, a novel surface chemistry was developed for anchoring of amyloid β (Aβ) peptides at their N-terminal moieties. The use of the site specific immobilization procedure allowed to measure the rupture of Aβ -Aβ contacts at single molecule level. The rupture of these contacts is accompanied by the extension of the peptide chain detected by a characteristic elasto-mechanical component of the forcedistance curves. Potential applications of the nanomechanical studies to understanding the mechanisms of development of protein misfolding diseases are discussed.

Probing Interactions within the Synaptic DNA-SfiI Complex by AFM Force Spectroscopy

“…An adhesive peak at the beginning of the force curve (section 1 of the force curve) is accompanied by a force extension curve (section 2) corresponding to the stretching of polymer linkers 22 , followed by a rupture event (section 3). 21 We interpret the magnitude of this force change as the force required to break the interactions between DNA and SfiI protein within the complex. This assumption was supported by control experiments in which the pulling was performed in a large excess of free duplex in solution.…”

“…17; 18; 19; 20 Such experiments often require covalent attachment of the target molecules, and we have recently developed and tested the surface chemistry which allows simple and reliable anchoring of target molecules with free thiol groups to a surface. 21 By using single molecule force spectroscopy, we measured the stability of the synaptic SfiI-DNA complex. We also used DFS to reveal the energy landscape for the SfiI-DNA complex dissociation, which is not accessible by any other technique.…”

Dynamic properties of pH-dependent structural organization of the amyloidogenic β-protein (1-40)

“…13,[35][36][37][38][39] It was demonstrated 13,38,39 that the aggregation rate of the Aβ fibril formation is much faster at the acidic pH compared to the neutral and basic pHs. Data obtained by solid state NMR spectroscopy 9 and atomic force microscopy experiments [40][41][42] also showed pH-dependent structural alterations of the Aβ monomers. On the other hand, pH values determine protonated and deprotonated states of the amino acid residues having ionogenic groups.…”

Artifacts in Atomic Force Microscopy of Biological Samples

“…Soft cantilevers (k = 0.06 N/m) are typically used for force spectroscopy measurements (Kransnoslobodtsev et al, 2005). When these cantilevers are used to study topography several artifacts can appear.…”

“…AFM is commonly used in biology to study proteins (Ukraintsev et al, 2007;Rezek et al, 2009), peptides (Kransnoslobodtsev et al, 2005), DNA (Hamon et al, 2007), tissues (Graham et al, 2010), viruses (Kuznetsov et al, 2003) and living cells (H. X. You & Yu, 1999).…”