Probing Molecular Interactions in Metal-Abeta Complexes and Supramolecular Coiled Coil Assemblies Using Electron Spin Resonance
Year: 2015
Type: article
Abstract: In this work we focus on details of Cu(II) coordination in amyloid-β (Aβ) peptide. Aggregation of Aβ, and modulation of morphology of aggregates by divalent metal ions, such as Cu(II) and Zn(II), are important in the etiology of Alzheimer’s disease. The metal ion coordination in amyloidogenic proteins are heterogeneous and involves one or more histidine residues. The Aβ peptide contains three histidine residues at positions 6, 13, and 14. The number of histidine residues coordinated to Cu(II) depends on environmental factors such as pH, Cu(II) concentration, presence of other metals, ionic strength etc. With the aid of electron spin resonance (ESR) we show that at physiological pH, Zn(II) ions selectively substitute Cu(II) ions coordinated to Aβ, and disrupt the distribution of Cu(II) population among different coordination modes. We also quantify the number of histidine residues coordinated to Cu(II) at higher pH of 8.7. Our results suggests that Cu(II) coordinated to simultaneous His13-His14 may lead to the formation of Aβ aggregates with more amorphous morphology. Furthermore we suggests the importance of His13 in the formation of ordered β-sheets. Overall we rationalize the impact of metal ion coordination in modulating the morphology of Aβ aggregates. In the second part of our research we examine the molecular origins of flexibility associated with supramolecular polymer subunits with double electron electron resonance (DEER) spectroscopy. It has been shown coiled coil subunits appended with different organic linkers, ethylenediamide (EDA) and piperazine (PIP), led to the formation of supramolecular polymer assemblies with different apparent hydrodynamic radii. With the strategic placement of the spin label near the cross linking site and near the N-terminus we were able to monitor range of conformations of each subunit when linked with the two linkers. Molecular dynamics simulations guided by DEER distance distributions were conducted to show that the PIP linker stabilizes a folded coiled coil population where the positioning of the cross linking site of outer helices is constrained. We suggest that this subpopulation facilitate the chain propagation in the same direction leading to the formation of polymers with larger hydrodynamic radius.
Author: K. Ishara Silva
Language: English
Subfield: Cellular and Molecular Neuroscience
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1168239705