1
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Pokutsa A, Tkach S, Zaborovsky A, Bloniarz P, Paczeŝniak T, Muzart J. Sustainable Oxidation of Cyclohexane and Toluene in the Presence of Affordable Catalysts: Impact of the Tandem of Promoter/Oxidant on Process Efficiency. ACS OMEGA 2020; 5:7613-7626. [PMID: 32280905 PMCID: PMC7144162 DOI: 10.1021/acsomega.0c00447] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Accepted: 03/17/2020] [Indexed: 06/11/2023]
Abstract
The oxygenation of cyclohexane and toluene by O2 and H2O2 catalyzed by VO(acac)2 and Co(acac)2 was studied at 40-100 °C and 1-10 atm. Upon such conditions, the process can be remarkably (30× times) enhanced by the minute (6-15 mM) additives of oxalic acid (OxalH) or N-hydroxyphthalimide (NHPI). The revealed effect of OxalH on H2O2-piloted oxidation is closely associated with the nature of the catalyst cation and boosted by VO(acac)2. Whereas the effectiveness of Co(acac)2-based systems was curbed by the addition of OxalH and remained much below the one displayed with the previous system. The observed conspicuous difference in activity was attributed to the substantially higher solubility of in situ formed VO(IV)oxalate compared to that of Co(II)oxalate. The exploration of H2O2 for the NHPI-promoted process leads to the decisively lower (5-7 times) yield in comparison to the O2-driven reaction. Similarly, for the O2-operated protocol, the yield cannot be improved by addition of OxalH either to VO(acac)2 + NHPI or to Co(acac)2 + NHPI mixture. By contrast, the combination of NHPI with VO(acac)2 or Co(acac)2 and particularly with the above two mixtures in O2-piloted oxidation enhances the yield of the aimed products 3-6 times regardless of the substrate used. The revealed significant synergetic effect of the cobalt + vanadyl bicomponent catalyst was due to the participation of each of its moiety in the different stages of the process mechanism. Only benzyl alcohol and benzaldehyde were identified in VO(acac)2- or Co(acac)2-catalyzed toluene oxidation, while cyclohexane oxidation yields cyclohexylhydroperoxide in line with cyclohexanol and cyclohexanone. The putative mechanism of investigated processes is highlighted and discussed.
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Affiliation(s)
- Alexander Pokutsa
- Department
of Physical Chemistry of Fuel Fossils NAS of Ukraine, Institute of Physical Organic Chemistry and Chemistry of Coal NAS
of Ukraine, Naukova Str.,
3A, Lviv 79060, Ukraine
| | - Sergiy Tkach
- Yuriya-Farm
Corp., Narodnogo Opolchennya
Str., 19, Kyiv 03151, Ukraine
| | - Andriy Zaborovsky
- Department
of Physical Chemistry of Fuel Fossils NAS of Ukraine, Institute of Physical Organic Chemistry and Chemistry of Coal NAS
of Ukraine, Naukova Str.,
3A, Lviv 79060, Ukraine
| | - Pawel Bloniarz
- Chemistry
Department, Rzeszow University of Technology, P.O. Box 85, Rzeszow 35-959, Poland
| | - Tomasz Paczeŝniak
- Chemistry
Department, Rzeszow University of Technology, P.O. Box 85, Rzeszow 35-959, Poland
| | - Jacques Muzart
- CNRS—Université
de Reims Champagne-Ardenne, Institut de Chimie Moléculaire
de Reims, UMR 7312, UFR des Sciences Exactes et Naturelles, BP 1039, Reims 51687, Cedex 2, France
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2
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Tang WK, Leong CP, Hao Q, Siu CK. Theoretical examination of competitive β-radical-induced cleavages of N–Cα and Cα–C bonds of peptides. CAN J CHEM 2015. [DOI: 10.1139/cjc-2015-0208] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Selective cleavages of N–Cα and Cα–C bonds of β-radical tautomers of amino acid residues in radical peptides have been examined theoretically by means of the density functional theory at the M06-2X/6-311++G(d,p) level. The majority of the bond cleavages are homolytic via β-scission. Their energy barriers depend largely on the ability of the radical being stabilized in the transition structures and the availability of a mobile proton in the vicinity of the β-radical center. The N–Cα bond is less favorably cleaved than the Cα–C bond (except Ser and Thr) for systems without a mobile proton. It is because, firstly, the homolytic cleavage is less favorable for the more polar N–Cα bond than for the less polar Cα–C bond. Secondly, a less stable σ-radical localized on the amide nitrogen atom of the incipient N-terminal fragment is formed for the former, while a more stable radical delocalized in a π*(CO)-like orbital of the incipient C-terminal fragment is formed for the latter. In the presence of a mobile proton N-terminal to the β-radical center, some degrees of heterolytic cleavage character, as preferred by the polar N–Cα bond, are observed. Consequently, its barrier is reduced. If the mobile proton is located at the C-terminal amide oxygen of the β-radical center, the Cα–C bond cleavage will be significantly suppressed. It is because the radical in the incipient C-terminal fragment becomes more localized as a σ-radical on the carbon atom of its protonated amide group. With basic amino acid residues, the Cα–C bond cleavage can be reactivated. Heterolytic cleavage of the polar N–Cα bond can be largely facilitated if a mobile proton N-terminal to the β-radical center is available and the radical in the incipient C-terminal fragment is sufficiently stabilized, for instance, by the aromatic side chain of Trp and Tyr. Therefore, cleavages of the N–Cα bond induced by the β-radical tautomer of Trp and Tyr are often preferred as compared with cleavages of the Cα–C bond in peptide radical cations containing mobile protons.
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Affiliation(s)
- Wai-Kit Tang
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
| | - Chun-Ping Leong
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
| | - Qiang Hao
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
| | - Chi-Kit Siu
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
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3
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Lee R, Coote ML. New insights into 1,2,4-trioxolane stability and the crucial role of ozone in promoting polymer degradation. Phys Chem Chem Phys 2013; 15:16428-31. [DOI: 10.1039/c3cp52863d] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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4
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Marque SRA, Siri D. β-Fragmentation of tertiary alkoxyl radicals: G3(MP2)-RAD and natural bond orbital investigations. Chemphyschem 2012; 13:703-7. [PMID: 22290686 DOI: 10.1002/cphc.201100708] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2011] [Revised: 12/17/2011] [Indexed: 11/09/2022]
Affiliation(s)
- Sylvain R A Marque
- UMR 5254-LCP (Laboratoire Chimie Provence), Université de Provence case 521, Marseille, France.
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5
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Morgan PE, Pattison DI, Davies MJ. Quantification of hydroxyl radical-derived oxidation products in peptides containing glycine, alanine, valine, and proline. Free Radic Biol Med 2012; 52:328-39. [PMID: 22064365 DOI: 10.1016/j.freeradbiomed.2011.10.448] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/04/2011] [Revised: 10/11/2011] [Accepted: 10/17/2011] [Indexed: 01/22/2023]
Abstract
Proteins are a major target for oxidation due to their abundance and high reactivity. Despite extensive investigation over many years, only limited quantitative data exist on the contributions of different pathways to the oxidation of peptides and proteins. This study was designed to obtain quantitative data on the nature and yields of oxidation products (alcohols, carbonyls, hydroperoxides, fragment species) formed by a prototypic oxidant system (HO(•)/O(2)) on small peptides of limited, but known, amino acid composition. Peptides composed of Gly, Ala, Val, and Pro were examined with particular emphasis on the peptide Val-Gly-Val-Ala-Pro-Gly, a repeat motif in elastin with chemotactic activity and metalloproteinase regulation properties. The data obtained indicate that hydroperoxide formation occurs nonrandomly (Pro > Val > Ala > Gly) with this inversely related to carbonyl yields (both peptide-bound and released). Multiple alcohols are generated at both side-chain and backbone sites. Backbone fragmentation has been characterized at multiple positions, with sites adjacent to Pro residues being of major importance. Summation of the product concentrations provides clear evidence for the occurrence of chain reactions in peptides exposed to HO(•)/O(2), with the overall product yields exceeding that of the initial HO(•) generated.
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Affiliation(s)
- Philip E Morgan
- Free Radical Group, The Heart Research Institute, 7 Eliza Street, Newtown, Sydney, NSW 2042, Australia.
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6
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Vereecken L, Francisco JS. Theoretical studies of atmospheric reaction mechanisms in the troposphere. Chem Soc Rev 2012; 41:6259-93. [DOI: 10.1039/c2cs35070j] [Citation(s) in RCA: 311] [Impact Index Per Article: 25.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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7
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Domingues P, Fonseca C, Reis A, Domingues MRM. Identification of isomeric spin adducts of Leu-Tyr and Tyr-Leu free radicals using liquid chromatography-tandem mass spectrometry. Biomed Chromatogr 2011; 26:51-60. [DOI: 10.1002/bmc.1624] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2010] [Revised: 01/22/2011] [Accepted: 01/24/2011] [Indexed: 01/08/2023]
Affiliation(s)
- Pedro Domingues
- Mass Spectrometry Centre; Department of Chemistry; University of Aveiro; 3810-193; Aveiro; Portugal
| | - Conceição Fonseca
- Mass Spectrometry Centre; Department of Chemistry; University of Aveiro; 3810-193; Aveiro; Portugal
| | - Ana Reis
- Mass Spectrometry Centre; Department of Chemistry; University of Aveiro; 3810-193; Aveiro; Portugal
| | - M. Rosário M. Domingues
- Mass Spectrometry Centre; Department of Chemistry; University of Aveiro; 3810-193; Aveiro; Portugal
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8
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Influence of amino acid relative position on the oxidative modification of histidine and glycine peptides. Anal Bioanal Chem 2011; 399:2779-94. [DOI: 10.1007/s00216-011-4668-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2010] [Revised: 12/05/2010] [Accepted: 01/05/2011] [Indexed: 10/18/2022]
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9
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Barlow CK, Wright A, Easton CJ, O'Hair RAJ. Gas-phase ion-molecule reactions using regioselectively generated radical cations to model oxidative damage and probe radical sites in peptides. Org Biomol Chem 2011; 9:3733-45. [DOI: 10.1039/c0ob01245a] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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10
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Abouelatta AI, Campanali AA, Ekkati AR, Shamoun M, Kalapugama S, Kodanko JJ. Oxidation of the Natural Amino Acids by a Ferryl Complex: Kinetic and Mechanistic Studies with Peptide Model Compounds. Inorg Chem 2009; 48:7729-39. [DOI: 10.1021/ic900527c] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Ahmed I. Abouelatta
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, Michigan 48202
| | - Ashley A. Campanali
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, Michigan 48202
| | - Anil R. Ekkati
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, Michigan 48202
| | - Mark Shamoun
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, Michigan 48202
| | - Suneth Kalapugama
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, Michigan 48202
| | - Jeremy J. Kodanko
- Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, Michigan 48202
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11
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Zhang L, Reilly JP. Radical-driven dissociation of odd-electron peptide radical ions produced in 157 nm photodissociation. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2009; 20:1378-1390. [PMID: 19477139 DOI: 10.1016/j.jasms.2009.03.026] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2009] [Revised: 03/30/2009] [Accepted: 03/31/2009] [Indexed: 05/27/2023]
Abstract
Odd-electron a + 1 radical ions generated in the 157 nm photodissociation of peptide ions were investigated in an ion trap mass spectrometer. To localize the radical, peptide backbone amide hydrogens were replaced with deuterium. When the resulting radical ions underwent hydrogen elimination, no H/D scrambling was obvious, suggesting that without collisional activation, the radical resides on the terminal alpha-carbon. Upon collisional excitation, odd-electron radical ions dissociate through two favored pathways: the production of a-type ions at aromatic amino acids via homolytic cleavage of backbone C(alpha)-C(O) bonds and side-chain losses at nonaromatic amino acids. When aromatic residues are not present, nonaromatic residues can also lead to a-type ions. In addition to a-type ions, serine and threonine yield c(n-1) and a(n-1) + 1 ions where n denotes the position of the serine or threonine. All of these fragments appear to be directed by the radical and they strongly depend on the amino acid side-chain structure. In addition, thermal fragments are also occasionally observed following cleavage of labile Xxx-Pro bonds and their formation appears to be kinetically competitive with radical migration.
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Affiliation(s)
- Liangyi Zhang
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, USA
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12
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Ly T, Julian RR. Tracking radical migration in large hydrogen deficient peptides with covalent labels: facile movement does not equal indiscriminate fragmentation. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2009; 20:1148-1158. [PMID: 19286394 DOI: 10.1016/j.jasms.2009.02.009] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2008] [Revised: 01/29/2009] [Accepted: 02/05/2009] [Indexed: 05/27/2023]
Abstract
Photodissociation of iodo-tyrosine modified peptides yields localized radicals on the tyrosine side chain, which can be further dissociated by collisional activation. We have performed extensive experiments on model peptides, RGYALG, RGYG, and their derivatives, to elucidate the mechanisms underlying backbone fragmentation at tyrosine. Neither acetylation nor deuteration of the tyrosyl phenolic hydrogen significantly affects backbone fragmentation. However, deuterium migration from the tyrosyl beta carbon is concomitant with cleavage at tyrosine. Substitution of tyrosine with 4-hydroxyphenylglycine, which does not have beta hydrogens, results in almost complete elimination of backbone fragmentation at tyrosine. These results suggest that a radical situated on the beta carbon is required for a-type fragmentation in hydrogen-deficient radical peptides. Replacement of the alphaH of the residue adjacent to tyrosine with methyl groups results in significant diminution of backbone fragmentation. The initial radical abstracts an alphaH from the adjacent amino acid, which is poised to "rebound" and abstract the betaH of tyrosine through a six-membered transition-state. Subsequent beta-scission leads to the observed a-type backbone fragment. These results from deuterated peptides clearly reveal that radical migration in peptides can occur and that multiple migrations are not infrequent. Counterintuitively, close examination of all experimental results reveals that the probability for fragmentation at a particular residue is well correlated with thermodynamic radical stability. A-type fragmentation therefore appears to be most likely when favorable thermodynamics are combined with the relevant kinetic control. These results are consistent with ab initio calculations, which demonstrate that barriers to migration are significantly smaller in magnitude than probable dissociation thresholds.
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Affiliation(s)
- Tony Ly
- Department of Chemistry, University of California, Riverside, California 92521, USA
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13
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Sun Q, Nelson H, Ly T, Stoltz BM, Julian RR. Side chain chemistry mediates backbone fragmentation in hydrogen deficient peptide radicals. J Proteome Res 2009; 8:958-66. [PMID: 19113886 DOI: 10.1021/pr800592t] [Citation(s) in RCA: 132] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
A crown ether based, photolabile radical precursor which forms noncovalent complexes with peptides has been prepared. The peptide/precursor complexes can be electrosprayed, isolated in an ion trap, and then subjected to laser photolysis and collision induced dissociation to generate hydrogen deficient peptide radicals. It is demonstrated that these peptide radicals behave very differently from the hydrogen rich peptide radicals generated by electron capture methods. In fact, it is shown that side chain chemistry dictates both the occurrence and relative abundance of backbone fragments that are observed. Fragmentation at aromatic residues occurs preferentially over most other amino acids. The origin of this selectivity relates to the mechanism by which backbone dissociation is initiated. The first step is abstraction of a beta-hydrogen from the side chain, followed by beta-elimination to yield primarily a-type fragment ions. Calculations reveal that those side chains which can easily lose a beta-hydrogen correlate well with experimentally favored sites for backbone fragmentation. In addition, radical mediated side chain losses from the parent peptide are frequently observed. Eleven amino acids exhibit unique mass losses from side chains which positively identify that particular amino acid as part of the parent peptide. Therefore, side chain losses allow one to unambiguously narrow the possible sequences for a parent peptide, which when combined with predictable backbone fragmentation should lead to greatly increased confidence in peptide identification.
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Affiliation(s)
- Qingyu Sun
- Department of Chemistry, University of California, Riverside, California 92521, USA
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14
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Can copper binding to the prion protein generate a misfolded form of the protein? Biometals 2009; 22:159-75. [PMID: 19140013 DOI: 10.1007/s10534-008-9196-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2008] [Accepted: 12/07/2008] [Indexed: 10/21/2022]
Abstract
The native prion protein (PrP) has a two domain structure, with a globular folded alpha-helical C-terminal domain and a flexible extended N-terminal region. The latter can selectively bind Cu(2+) via four His residues in the octarepeat (OR) region, as well as two sites (His96 and His111) outside this region. In the disease state, the folded C-terminal domain of PrP undergoes a conformational change, forming amorphous aggregates high in beta-sheet content. Cu(2+) bound to the ORs can be redox active and has been shown to induce cleavage within the OR region, a process requiring conserved Trp residues. Using computational modeling, we have observed that electron transfer from Trp residues to copper can be favorable. These models also reveal that an indole-based radical cation or Cu(+) can initiate reactions leading to protein backbone cleavage. We have also demonstrated, by molecular dynamics simulations, that Cu(2+) binding to the His96 and His111 residues in the remaining PrP N-terminal fragment can induce localized beta-sheet structure, allowing us to suggest a potential mechanism for the initiation of beta-sheet misfolding in the C-terminal domain by Cu(2+).
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15
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Pushie MJ, Vogel HJ. A potential mechanism for Cu2+ reduction, beta-cleavage, and beta-sheet initiation within the N-terminal domain of the prion protein: insights from density functional theory and molecular dynamics calculations. JOURNAL OF TOXICOLOGY AND ENVIRONMENTAL HEALTH. PART A 2009; 72:1040-1059. [PMID: 19697239 DOI: 10.1080/15287390903084389] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The N-terminal region of the native human prion protein encompasses four highly conserved octarepeats that each contain a single His, Pro, Gln, and Trp residue as well as several Gly residues. At neutral pH these repeats are capable of individually binding copper (Cu(2+)) ions, involving the His side chain and the backbone amide of the Gly residues. In addition, the two His residues at positions 96 and 111 are also capable of binding Cu(2+). At low concentrations of the metal ion or at low pH, one Cu(2+) may be bound by multiple His residues of the four octarepeats. This complex is known to be redox active, while none of the other Cu(2+)-bound complexes are. Using density functional theory and molecular dynamics calculations data demonstrated how this form of the protein could reduce Cu(2+), through a process involving electron transfer from the Trp side chain. The reduced Cu gives rise to reactive oxygen species (ROS), which can lead to beta-cleavage of the prion protein chain at any of the Gly residues around position 90. Protein fragments of lengths similar to those arising from beta-cleavage are predominantly found in both healthy and Creutzfeldt-Jakob disease (CJD)-affected brains. Models of Cu binding to the His96 and His111 residues also indicate that different modes of Cu(2+) binding result in formation of stable beta-hairpin structures in this region of the protein. It is postulated that through interactions with the C-terminal part of the protein these hairpins may initiate misfolding and yield more stable beta-sheet structures that might associate in the same fashion with additional prion proteins.
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Affiliation(s)
- M Jake Pushie
- Structural Biology Research Group, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
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