Heme-Aβ in SDS micellar environment: Active site environment and reactivity

Alzheimer's disease (AD), the most common cause of dementia, is a progressive neurodegenerative disorder that causes brain cell death. Oxidative stress derived from the accumulation of redox cofactors like heme in amyloid plaques originating from amyloid β (Aβ) peptides has been implicated in the pathogenesis of AD. In the past our group has studied the interactions and reactivities of heme with soluble oligomeric and aggregated forms of Aβ. In this manuscript we report the interaction of heme with Aβ that remains membrane bound using membrane mimetic SDS (sodium dodecyl sulfate) micellar medium. Employing different spectroscopic techniques viz. circular dichroism (CD), absorption (UV-Vis), electron paramagnetic resonance (EPR) and resonance Raman (rR) we find that Aβ binds heme using one of its three His (preferentially His13) in SDS micellar medium. We also find that Arg5 is an essential distal residue responsible for higher peroxidase activity of heme bound Aβ in this membrane mimetic environment than free heme. This peroxidase activity exerted by even membrane bound heme-Aβ can potentially be more detrimental as the active site remains close to membranes and can hence oxidise the lipid bilayer of the neuronal cell, which can induce cell apoptosis. Thus, heme-Aβ in solution as well as in membrane-bound form are detrimental.

Molecular Mechanisms and Genetics of Oxidative Stress in Alzheimer's Disease

Alzheimer’s disease is the most common neurodegenerative disorder that can cause dementia in elderly over 60 years of age. One of the disease hallmarks is oxidative stress which interconnects with other processes such as amyloid-β deposition, tau hyperphosphorylation, and tangle formation. This review discusses current thoughts on molecular mechanisms that may relate oxidative stress to Alzheimer’s disease and identifies genetic factors observed from in vitro, in vivo, and clinical studies that may be associated with Alzheimer’s disease-related oxidative stress.

Nitrite reductase activity of heme and copper bound Aβ peptides

A significant abundance of copper (Cu) and iron in amyloid β (Aβ) plaques, and several heme related metabolic disorders are directly correlated with Alzheimer's disease (AD), and these together with co-localization of Aβ plaques with heme rich deposits in the brains of AD sufferers indicates a possible association of the said metals with the disease. Recently, the Aβ peptides have been found to bind heme and Cu individually as well as simultaneously. Another significant finding relevant to this is the lower levels of nitrite and nitrate found in the brains of patients suffering from AD. In this study, a combination of absorption and electron paramagnetic resonance spectroscopy and kinetic assays have been used to study the interaction of nitrite with the metal bound Aβ complexes. The data indicate that heme(III)-Cu(i)-Aβ, heme(II)-Cu(i)-Aβ, heme(II)-Aβ and Cu(i)-Aβ can reduce nitrite to nitric oxide (NO), an important biological messenger also related to AD, and thus behave as nitrite reductases. However these complexes reduce nitrite at different rates with heme(III)-Cu(i)-Aβ being the fastest following an inner sphere electron transfer mechanism. The rest of the metal-Aβ adducts follow an outer sphere electron transfer mechanism during nitrite reduction. Protonation from the Arg5 residue triggering the N-O bond heterolysis in heme(III) bound nitrite with a simultaneous electron transfer from the Cu(i) center to produce NO is the rate determining step, indicating a proton transfer followed by electron transfer (PTET) mechanism.

Cu and Zn interactions with Aβ peptides: consequence of coordination on aggregation and formation of neurotoxic soluble Aβ oligomers

The coordination chemistry of transition metal ions (Fe, Cu, Zn) with the amyloid-β (Aβ) peptides has attracted a lot of attention in recent years due to its repercussions in Alzheimer's disease (AD).

Metal Binding to Aβ Peptides Inhibits Interaction with Cytochrome c: Insights from Abiological Constructs

Aβ(1-40) peptide is mutated to introduce cysteine residue to allow formation of organized self-assembled monolayers (SAMs) on Au electrodes. Three mutants of this peptide are produced, which vary in the position of the inserted cysteine residue. Fourier transform infrared data on these peptide SAMs show the presence of both α helices and β sheet in these Aβ constructs. These peptide constructs interact with cytochrome c (Cytc), allowing electron transfer between Cytc and the electrode via the Aβ peptides. Binding of metals like Zn2+ or Cu2+ induces changes in the morphologies of these assemblies, making them fold, which inhibits their spontaneous interaction with Cytc.