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Alzheimer's disease (AD) is characterized by the abnormal aggregation of amyloid ß (Aß) peptide in extracellular deposits generated upon proteolysis of Amyloid Precursor Protein (APP). While copper (Cu(II)) binds to Aß in soluble oligomeric and aggregated forms, its interaction with membrane-bound Aß remains elusive. Investigating these interactions is crucial for understanding AD pathogenesis. Here, utilizing SDS micelles as a simplified membrane mimic, we focus on elucidating the interplay between membrane-anchored Aß and copper, given their pivotal roles in AD. We employed spectroscopic techniques including UV, CD, and EPR to characterize the active site of Cu-Aß complexes. Our findings demonstrate that copper interacts with Aß peptides in membrane-mimicking micellar environments similarly to aqueous buffer solutions. Cu-Aß complexes in this medium also induce higher hydrogen peroxide (H2O2) production, potentially contributing to AD-related oxidative stress. Moreover, we observe an increased oxidation rate of neurotransmitter such as dopamine by Cu-Aß complexes. These results enhance our understanding of Cu-Aß interactions in AD pathology and offer insights into potential therapeutic interventions targeting this interaction.
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An azadithiolate bridged CN- bound pentacarbonyl bis-iron complex, mimicking the active site of [Fe-Fe] H2ase is synthesized. The geometric and electronic structure of this complex is elucidated using a combination of EXAFS analysis, infrared and Mössbauer spectroscopy and DFT calculations. The electrochemical investigations show that complex 1 effectively reduces H+ to H2 between pH 0-3 at diffusion-controlled rates (1011 M-1 s-1) i.e. 108 s-1 at pH 3 with an overpotential of 140 mV. Electrochemical analysis and DFT calculations suggests that a CN- ligand increases the pKa of the cluster enabling hydrogen production from its Fe(i)-Fe(0) state at pHs much higher and overpotential much lower than its precursor bis-iron hexacarbonyl model which is active in its Fe(0)-Fe(0) state. The formation of a terminal Fe-H species, evidenced by spectroelectrochemistry in organic solvent, via a rate determining proton coupled electron transfer step and protonation of the adjacent azadithiolate, lowers the kinetic barrier leading to diffusion controlled rates of H2 evolution. The stereo-electronic factors enhance its catalytic rate by 3 order of magnitude relative to a bis-iron hexacarbonyl precursor at the same pH and potential.
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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 ß (Aß) 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 Aß. In this manuscript we report the interaction of heme with Aß 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 Aß 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 Aß in this membrane mimetic environment than free heme. This peroxidase activity exerted by even membrane bound heme-Aß 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-Aß in solution as well as in membrane-bound form are detrimental.
Assuntos
Doença de Alzheimer , Peptídeos beta-Amiloides , Humanos , Peptídeos beta-Amiloides/química , Heme/química , Domínio Catalítico , Micelas , Doença de Alzheimer/metabolismo , Espectroscopia de Ressonância de Spin Eletrônica , Peroxidases/metabolismoRESUMO
The reduction of SO2 to fixed forms of sulfur can address the growing concerns regarding its detrimental effect on health and the environment as well as enable its valorization into valuable chemicals. The naturally occurring heme enzyme sulfite reductase (SiR) is known to reduce SO2 to H2 S and is an integral part of the global sulfur cycle. However, its action has not yet been mimicked in artificial systems outside of the protein matrix even after several decades of structural elucidation of the enzyme. While the coordination of SO2 to transition metals is documented, its reduction using molecular catalysts has remained elusive. Herein reduction of SO2 by iron(II) tetraphenylporphyrin is demonstrated. A combination of spectroscopic data backed up by theoretical calculations indicate that FeII TPP reduces SO2 by 2e- /2H+ to form an intermediate [FeIII -SO]+ species, also proposed for SiR, which releases SO. The SO obtained from the chemical reduction of SO2 could be evidenced in the form of a cheletropic adduct of butadiene resulting in an organic sulfoxide.
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Redox active metallo-proteins and metallo-peptides attached to self-assembled monolayers (SAM) of thiols on Au electrodes or constituting the SAM on Au electrodes can provide unique opportunities to investigate a range of complicated biological phenomena in controlled abiological constructs. In addition to conventional biochemical tools like site-directed mutagenesis, these constructs allow control over electron transfer (ET) processes, micro solvation (SAM design), folding/misfolding and orientation of these biological entities. This article presents a review of the work done by this group in creating abiological bio-inspired SAM on Au electrodes to probe several important biological processes where redox plays or might play a major role. These include stabilisation of different morphologies of Aß peptides and which allow investigation of the reactivity of their Cu/Zn/heme-bound forms, determination of both outer-sphere and inner-sphere reorganisation energies of cytochrome c along with deciphering the role of the fluxional methionine and finally creation of bio-chemical constructs of cytochrome c oxidase which not only reduce O2 selectively to H2O efficiently but also provide key insights in O2 reduction mechanism which has aided the development of efficient artificial catalysts.
Assuntos
Heme , Peptídeos , Eletrodos , Transporte de Elétrons , Heme/metabolismo , OxirreduçãoRESUMO
With the price-competitiveness of solar and wind power, hydrogen technologies may be game changers for a cleaner, defossilized, and sustainable energy future. H2 can indeed be produced in electrolyzers from water, stored for long periods, and converted back into power, on demand, in fuel cells. The feasibility of the latter process critically depends on the discovery of cheap and efficient catalysts able to replace platinum group metals at the anode and cathode of fuel cells. Bioinspiration can be key for designing such alternative catalysts. Here we show that a novel class of iron-based catalysts inspired from the active site of [FeFe]-hydrogenase behave as unprecedented bidirectional electrocatalysts for interconverting H2 and protons efficiently under near-neutral aqueous conditions. Such bioinspired catalysts have been implemented at the anode of a functional membrane-less H2/O2 fuel cell device.
Assuntos
Hidrogenase , Proteínas Ferro-Enxofre , Catálise , Domínio Catalítico , Hidrogênio/química , Hidrogenase/química , Proteínas Ferro-Enxofre/química , Prótons , ÁguaRESUMO
A significant abundance of copper (Cu) and iron in amyloid ß (Aß) plaques, and several heme related metabolic disorders are directly correlated with Alzheimer's disease (AD), and these together with co-localization of Aß plaques with heme rich deposits in the brains of AD sufferers indicates a possible association of the said metals with the disease. Recently, the Aß 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 Aß complexes. The data indicate that heme(III)-Cu(i)-Aß, heme(II)-Cu(i)-Aß, heme(II)-Aß and Cu(i)-Aß 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)-Aß being the fastest following an inner sphere electron transfer mechanism. The rest of the metal-Aß 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.
Assuntos
Peptídeos beta-Amiloides/química , Cobre/química , Heme/química , Nitrito Redutases/química , Espectroscopia de Ressonância de Spin Eletrônica , Transporte de Elétrons , Humanos , Ferro/química , Cinética , Óxido Nítrico/química , Nitritos/química , Oxirredução , Placa Amiloide/químicaRESUMO
Redox active iron is utilized in biology for various electron transfer and catalytic reactions essential for life, yet this same chemistry mediates the formation of partially reduced oxygen species (PROS). Oxidative stress derived from the iron accumulated in the amyloid plaques originating from amyloid ß (Aß) peptides and neurofibrillary tangles derived from hyperphosphorylated tau proteins has been implicated in the pathogenesis of Alzheimer's disease (AD). Altered heme homeostasis leading to dysregulation of expression of heme proteins and heme deposits in the amyloid plaques are characteristic of the AD brain. However, the pathogenic significance of heme in neurodegeneration in AD has been unappreciated due to the lack of detailed understanding of the chemistry of the interaction of heme and Aß peptides. As a result, the biochemistry and biophysics of heme complexes of Aß peptides (heme-Aß) remained largely unexplored. In this Account, we discuss the active site environment of heme bound Aß complexes, which involves three amino acid residues unique in mammalian Aß (Arg5, Tyr10, and His13) and missing in Aß from rodents, which do not get affected by AD. The histidine residue binds heme, while the arginine and the tyrosine act as key second sphere residues of the heme-Aß active site that play a crucial role in its reactivity. Generation of PROS, enhanced peroxidase activity, and oxidation of neurotransmitters such as serotonin (5-HT) are all found to be catalyzed by heme-Aß in in vitro assays, and these reactivities can potentially be linked to the observed neuropathologies in AD brain. Association of Cu with heme-Aß leads to the formation of heme-Cu-Aß. The heme-Cu-Aß complex produces a greater amount of PROS than reduced heme-Aß or Cu-Aß alone. Nitric oxide (NO), a signaling molecule, is found to ameliorate the detrimental effects of heme-Aß and Cu bound heme-Aß complexes by detaching heme from the heme-Aß complex and releasing it into the environment solution. Heme-Aß complexes show fast electron transfer with oxidized cytochrome c and rapid heme transfer with apomyoglobin and aponeuroglobin. NO, cytochrome c, and apoglobins can all lead to reduction in PROS generated by reduced heme-Aß. Synthetic analogues of heme, offering a hydrophobic distal environment, have been used to trap oxygen bound intermediates, which provides insight into the mechanism of PROS generation by reduced heme-Aß. Artificial constructs of Aß on nonbiological platforms are used not only to stabilize metastable and physiologically relevant large and small amyloid aggregates but also to monitor the interaction of various drug candidates with heme and Cu bound Aß aggregates, representing a tractable avenue for testing therapeutic agents targeting metals and cofactors in AD.