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 beta (Abeta) peptides at their N-terminal moieties. The use of the site specific immobilization procedure allowed to measure the rupture of Abeta-Abeta 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 force-distance curves. Potential applications of the nanomechanical studies to understanding the mechanisms of development of protein misfolding diseases are discussed.

Figure 1

Schemes illustrating the rupture of the protein in folded (low affinity, green arrows) and misfolded conformations (high affinity with multiple contact points-red wave shape).

Figure 2A

A typical force curve obtained for probing the Aβ-Aβ interaction at pH 5.6. The histogram summarizing the rupture force measurements is inserted into the figure.

Figure 2B

A force curve for the Aβ-Aβ interaction at pH 3.7. The arrowhead (red) points to the Aβ-Aβ rupture event. Insert (i) shows the histogram for the Aβ-Aβ rupture force values. Black line above the arrowhead shows the WLC approximation fit.

Figure 2C

The histogram of the extension distance for the Aβ-Aβ dimer rupture measured from the force curves obtained at pH 3.7

Figure 2D

The histogram of the force rupture values for the Aβ-Aβ dimer measured from the force curves obtained at pH.2.

Scheme 1

Synthesis of maleimide-PEG-silatrane 8

Scheme 2

Immobilization of amyloid peptide-cys on a functionalized mica surface