From Amyloid to Copper Arrays: The design of a functional Metalloamyloid Nanostructure (MAN) Open Access

Rengifo, Rolando (2017)

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Amyloidogenic diseases are characterized by abnormal collections of self-assembling peptides that form beautifully organized peptide arrays. Amyloid-β (Aβ), a hallmark protein in Alzheimer's Disease (AD), forms aggregates that have been linked with AD etiology, though their role in disease onset and progression has been poorly correlated. Recent efforts have brought Aβ to the forefront of AD research once again, however, as the intermediate stages of assembly have been identified as neurotoxic pathologies. In this work, we outline the first example of a fully characterized oligomeric particle - a marker in the working hypothesis of AD progression - formed from an extension of the Aβ nucleating core, Aβ(13-21)K16A (K16A). Motivated by the functional capacity ascribed to such small self-assembling units, and having characterized the well-organized supramolecular fibers that evolve from these oligomeric intermediates, we sought to modify their assembly pathway and tailor their function by incorporating redox active metal ions. In the presence of Cu2+, K16A fibers transform to form nanoribbons with a rich blue color. The K16A-Cu2+ metalloamyloid nanostructure (MAN) displays characteristics parallel to cupredoxins. We demonstrate, however, that Cu2+ is incorporated at a density ratio between 0.6 and 0.8 (Cu2+/peptide), insulated within a peptide bilayer in two distinct coordination environments regularly arrayed throughout the MAN. Indeed, these structures are composed of cupredoxin arrays with a redox potential of +670 mV vs. RHE. Furthermore, this MAN displays quasi-reversible redox behavior, and it can undergo substrate level reduction with no effect on its overall morphology over a period of at least 16 hrs. The level of stability, order, and homogeneity achieved in the design of this material coupled with the degree of Cu2+ incorporation insulated in a peptide bilayer and directing the rearrangement of the peptide arrays, makes the K16A-Cu2+ MAN a functional material unlike any other. Such a material paves the way for the rational design of new materials that will increase the complexity of MANs to demonstrate electron transport over controlled distances, electron storage in high density and redox chemistry within the self-assembling core.

Table of Contents

Table of Contents

Chapter 1 : Amyloid Applications in Nanobiotechnology. 1

  • Introduction. 1
  • Toward Conducting and Energy-Storing Amyloids. 4
  • Designing an Amyloid Antenna. 4
  • Breaking Amyloid Assembly Symmetry. 9
  • Metalloamyloid Nanostructures. 12
  • Rational Design of Small-Molecule Incorporating Amyloid Nanostructures. 19
  • Conclusion. 20

Chapter 2 : Dynamics of Amyloid Granules in the Oligomer Cascade Hypothesis. 23

  • Introduction. 23
  • Results and Discussion. 25
  • Oligomeric Particles and Supramolecular Fibers of H-H13HQALVFFA21-NH2 (K16A) 25
  • Defining the Structure of K16A Oligomeric Particles. 28
  • Conclusion. 37
  • Materials and Methods. 39

Chapter 3 : Designing Metalloamyloid Nanostructures (MANs) 52

  • Introduction. 52
  • Results and Discussion. 55
  • Peptide Design. 55
  • Templating K16A and Ac-K16A assembly with metals. 66
  • Cu2+ and Zn2+ influence on Ac-K16A and K16A assembly and morphology. 73
  • Solid-state NMR analysis of Ac-K16A and K16A assemblies in the presence of Zn2+. 87
  • Structure and stability of Ac-K16A-Cu2+ and K16A-Cu2+ MANs. 99
  • Reversibility of Cu2+/Cu+ cycle in Ac-K16A-Cu2+ and K16A-Cu2+ MANs. 112
  • Conclusion. 120
  • Materials and Methods. 123

Chapter 4 : Metalloamyloid Nanostructure (MAN) as a Blue Copper Protein Mimic. 132

  • Introduction. 132
  • Results and Discussion. 134
  • A ratiometric study of Cu2+ incorporation by optical spectroscopy and ITC.. 134
  • EPR analysis of K16A-Cu2+ nanostructures. 148
  • Cu2+ is isolated in the K16A peptide bilayer, not at the nanoribbon surface. 150
  • Assessing K16A-Cu2+ reactivity. 171
  • Conclusion. 183
  • Materials and Methods. 194

Chapter 5 What next?. 201

  • Non-canonical amino-acids serve as e- acceptors in the presence of Cu2+. 202
  • Peptide driven polyoxometalate (POM) self-assembly. 204
  • Expanding the complexity of self-assembling nanostructures by rational design. 206
  • Conclusion. 212

References. 213

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