14N electron spin echo envelope modulation Spectroscopy of Cu(II)-imidazole coordination structure in the amyloid- beta protein of Alzheimer's disease and in model Amyloid-beta peptides and complexes Open Access

Hernandez-Guzman, Jessica (2010)

Permanent URL: https://etd.library.emory.edu/concern/etds/2j62s506q?locale=en
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Abstract

Aggregation and fibrillization of the amyloid-beta (Abeta) protein and deposition in the form of plaques are the hallmarks of Alzheimer's disease. The coordination of Cu(II) by Abeta has been proposed to play a role in these processes. To gain insight into factors that govern fibrillization, electron paramagnetic resonance and electron spin echo envelope modulation (ESEEM) spectroscopies have been used to reveal features of the molecular structure of the Cu(II)- imidazole coordination in cryotrapped soluble and fibrillar forms of Abeta peptides [Abeta(1-40), Abeta(1-16), Abeta(13-21)] and model complexes [Cu(II)-diethylenetriamine-2-methylimidazole, Cu(II)-bis-histamine-bis-nitrate, Cu(II)-bis-(acetate)-bis-(2-methylimidazole)]. The relative orientation of the imidazoles is determined through the 2 v dq line shape. A method is developed for determination of the mutual orientation of the imidazole ligands, which is based on hybrid optimization simulations (OPTESIM) of the 14N ESEEM from the remote imidazole nitrogen in Cu(II) model complexes with particular focus on the double quantum harmonic component. The technique reveals a bis-cis-imidazole coordination geometry in Abeta(13-21)H14A fibrils. Orientation selection ESEEM was performed on the Cu(II) model complexes, to relate the imidazole and Cu(II) molecular axes. Qualitative agreement with X-ray crystallographic results was obtained and the method was applied to Abeta(13-21) peptides. The number of coordinated histidine imidazoles in Cu(II)-Abeta(1-40) is addressed by ESEEM of 15N-His13 or 15N-His14 peptides. Fibrillar 15N-labeled Abeta(1-40) gave comparable ESEEM, which is characteristic of His2 coordination. Soluble Abeta(1-16) and Abeta(1-40) showed ESEEM that is intermediate between His2 and His3 coordination. Additional data is required for a consistent interpretation of these results. Overall, the results demonstrate the power of ESEEM for the determination of the three-dimensional molecular structure of Cu(II)-imidazole coordination, which can be applied to gain insight into the fibrillization process in Cu(II)-Abeta peptide complexes.

Table of Contents

Table of Contents

Chapter 1: Introduction to Ab and metal ions interactions with Ab . 16

1.1 Structure and assembly of amyloid-b . 18

1.2 Metals ions and b-amyloid . 21

1.3 Structural models for metal ion binding to Ab fibrils . 23

1.3.1 Three dimensional proposed models for Ab fibrils . 23

1.3.2 Metal Ions in the association of Ab fibrils . 25

Chapter 2: Fundamentals . 31

2.1 Continuous Wave Electron Paramagnetic Resonance (CW-EPR) 32

2.2 Electron Spin Echo Envelope Modulation (ESEEM) 44

2.2.1 Spin Echo Phenomenon: Classical description . 45

2.2.2 Nuclear Modulation Effect 51

2.2.3 Exact Cancellation: Nuclear quadrupole interactions . 54

2.2.4 Orientation Selection . 58

2.2.4.1 Anisotropic dipolar hyperfine . 58

2.2.5 Double quantum harmonic analysis . 63

Chapter 3: Selection and synthesis of Cu(II) model complexes . 66

3.1 Cu(II) model complexes . 67

Single imidazole: Cu(II)(Dien)(2-MeIm) 67

Bis-trans imidazole: Cu(II)(Him)2(NO3)2. 68

Bis-cis imidazole: Cu(II)(2-MeIm)2(OAc)2 68

3.2 Ab peptides . 69

Synthesis of Ab(13-21) peptides: 71

Synthesis of Ab(1-40) peptide . 71

Synthesis of Ab(1-16) peptide . 72

Chapter 4: Applications of 2n dq, double quantum harmonic, analysis to Cu(II) model and Cu(II)-Ab complexes . 73

4.1 Motivation . 74

4.2 EPR Spectroscopy of Cu(II)-imidazole model complexes and A b peptides. 75

4.3. ESEEM Spectroscopy . 77

4.3.1 ESEEM results for Cu(II) model complexes. 77

4.3.2 ESEEM results for Cu(II)-A b complexes . 83

4.3.3 ESEEM simulation . 87

4.3.4 Simulation of the 14N ESEEM from the different Cu(II) complexes. 90

4.3.5 Mutual Orientation of Imidazole Ligands in Cu(II) model complexes . 91

4.3.5.1 Mutual Orientation of Imidazole Ligands in the Cu(II)(him)2(NO3)2 Complex . 91

4.3.5.2 Mutual Orientation of Imidazole Ligands in the Cu(II)(2-MeIm)2(OAc)2 Complex . 93

4.4 Assessment of the ESEEM Method of bis-Imidazole Coordination Geometry Determination in Cu(II) Complexes. 95

4.5 Mutual Orientation of Imidazole Ligands in the Cu(II)-Ac-A b (13-21)H14A Peptide. 97

4.6 Structuring of Ac-A b (13-21)H14A Fibrils by Cu(II) 98

Chapter 5: Orientation selection ESEEM of Cu(II) model complexes 101

5.1 Orientation selection of n dq feature in Cu(II) model complexes . 104

5.1.1 Single Imidazole: Cu(II)(Dien)(2-MeIm) 106

5.1.2 Bis-trans imidazole: Cu(II)(Him)2(NO3)2 108

5.1.3 Bis-cis imidazole: Cu(II)(2-MeIm)2(OAc)2 110

5.1.4 Qualitative Interpretation of the orientation dependence of the n dq feature . 112

5.2 Orientation selection of n dq feature in Cu(II)-Ab complexes . 119

5.2.1 Single Imidazole: Ab(13-21)K16A .. 119

5.2.2 Bis-imidazole: Ac-Ab(13-21)H14A .. 121

5.3 Orientation selection of double quantum harmonic, 2 n dq, feature in bis-imidazole Cu(II) models . 123

Chapter 6: Powder ESEEM of 15N- and 13C- labeled Cu(II)-Ab complexes 130

6.1 Background . 131

6.2 Using the ESEEM waveform as a tool for ligand identification . 132

6.2.1 Labeled Ab(1-40)-13C-15N samples . 135

6.2.2 Unlabeled Ab(1-40) and Ab(1-16) 143

6.3 Literature review for the conundrum of the number of histidines involved on the Cu(II)-Ab(1-16/40) binding site 147

Chapter 7: Conclusions and future directions . 149

Bibliography: 155

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