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Liu H, Yu Z, Liu L, Dong S. Cell Wall Binding Strategies Based on Cu 3SbS 3 Nanoparticles for Selective Bacterial Elimination and Promotion of Infected Wound Healing. ACS APPLIED MATERIALS & INTERFACES 2024; 16:33038-33052. [PMID: 38961578 DOI: 10.1021/acsami.4c04726] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/05/2024]
Abstract
Utilizing nanomaterials as an alternative to antibiotics, with a focus on maintaining high biosafety, has emerged as a promising strategy to combat antibiotic resistance. Nevertheless, the challenge lies in the indiscriminate attack of nanomaterials on both bacterial and mammalian cells, which limits their practicality. Herein, Cu3SbS3 nanoparticles (NPs) capable of generating reactive oxygen species (ROS) are discovered to selectively adsorb and eliminate bacteria without causing obvious harm to mammalian cells, thanks to the interaction between O of N-acetylmuramic acid in bacterial cell walls and Cu of the NPs. Coupled with the short diffusion distance of ROS in the surrounding medium, a selective antibacterial effect is achieved. Additionally, the antibacterial mechanism is then identified: Cu3SbS3 NPs catalyze the generation of O2•-, which has subsequently been conversed by superoxide dismutase to H2O2. The latter is secondary catalyzed by the NPs to form •OH and 1O2, initiating an in situ attack on bacteria. This process depletes bacterial glutathione in conjunction with the disruption of the antioxidant defense system of bacteria. Notably, Cu3SbS3 NPs are demonstrated to efficiently impede biofilm formation; thus, a healing of MRSA-infected wounds was promoted. The bacterial cell wall-binding nanoantibacterial agents can be widely expanded through diversified design.
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Affiliation(s)
- Hao Liu
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, PR China
- School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei, Anhui 230026, PR China
| | - Zhixuan Yu
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, PR China
- School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei, Anhui 230026, PR China
| | - Ling Liu
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, PR China
| | - Shaojun Dong
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin 130022, PR China
- School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei, Anhui 230026, PR China
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Bonczidai-Kelemen D, Tóth K, Fábián I, Lihi N. The role of the terminal cysteine moiety in a metallopeptide mimicking the active site of the NiSOD enzyme. Dalton Trans 2024; 53:1648-1656. [PMID: 38168682 DOI: 10.1039/d3dt03638c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
Superoxide dismutase (SOD) enzymes are pivotal in regulating oxidative stress. In order to model Ni containing SOD enzymes, the results of the thermodynamic, spectroscopic and SOD activity studies on the complexes formed between nickel(II) and a NiSOD related peptide, CysCysAspLeuProCysGlyValTyr-NH2 (wtCC), are reported. Cysteine was introduced to replace the first histidine residue in the amino acid sequence of the active site of the NiSOD enzyme. The novel peptide exhibits 3 times higher metal binding affinity compared to the native NiSOD fragment. This is due to the presence of the first cysteine in the coordination sphere of nickel(II). At physiological pH, the (NH2,S-,S-,S-) coordinated complex is the major species. This coordination mode is altered when one thiolate group is replaced by an amide nitrogen of the peptide backbone above pH 7.5. The nickel complexes of wtCC exhibit similar SOD activity to that of the complex formed with the active site fragment of the native NiSOD. The reaction between the complexes and the superoxide anion was studied by the sequential stopped-flow method. These studies revealed that the nickel(II) complex is always in excess over the nickel(III) complex during the dismutation process. However, the nickel(III) species is also involved in a relatively fast degradation process. This unambiguously proves that a protective mechanism must be operative in the NiSOD enzyme which prevents the oxidation of the sulfur atom of cysteine in the presence of O2-. The results provide new possibilities for the use of NiSOD mimics in bio- and industrial catalytic processes.
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Affiliation(s)
- Dóra Bonczidai-Kelemen
- HUN-REN-UD Mechanisms of Complex Homogeneous and Heterogeneous Chemical Reactions Research Group, Department of Inorganic and Analytical Chemistry, Faculty of Science and Technology, University of Debrecen, H-4032 Debrecen, Hungary.
- Doctoral School of Chemistry, University of Debrecen, Debrecen H-4032, Hungary
| | - Klaudia Tóth
- HUN-REN-UD Mechanisms of Complex Homogeneous and Heterogeneous Chemical Reactions Research Group, Department of Inorganic and Analytical Chemistry, Faculty of Science and Technology, University of Debrecen, H-4032 Debrecen, Hungary.
| | - István Fábián
- HUN-REN-UD Mechanisms of Complex Homogeneous and Heterogeneous Chemical Reactions Research Group, Department of Inorganic and Analytical Chemistry, Faculty of Science and Technology, University of Debrecen, H-4032 Debrecen, Hungary.
| | - Norbert Lihi
- HUN-REN-UD Mechanisms of Complex Homogeneous and Heterogeneous Chemical Reactions Research Group, Department of Inorganic and Analytical Chemistry, Faculty of Science and Technology, University of Debrecen, H-4032 Debrecen, Hungary.
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Ni J, Wood JL, White MY, Lihi N, Markham TE, Wang J, Chivers PT, Codd R. Reduction-cleavable desferrioxamine B pulldown system enriches Ni(ii)-superoxide dismutase from a Streptomyces proteome. RSC Chem Biol 2023; 4:1064-1072. [PMID: 38033724 PMCID: PMC10685849 DOI: 10.1039/d3cb00097d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2023] [Accepted: 10/02/2023] [Indexed: 12/02/2023] Open
Abstract
Two resins with the hydroxamic acid siderophore desferrioxamine B (DFOB) immobilised as a free ligand or its Fe(iii) complex were prepared to screen the Streptomyces pilosus proteome for proteins involved in siderophore-mediated Fe(iii) uptake. The resin design included a disulfide bond to enable the release of bound proteins under mild reducing conditions. Proteomics analysis of the bound fractions did not identify proteins associated with siderophore-mediated Fe(iii) uptake, but identified nickel superoxide dismutase (NiSOD), which was enriched on the apo-DFOB-resin but not the Fe(iii)-DFOB-resin or the control resin. While DFOB is unable to sequester Fe(iii) from sites deeply buried in metalloproteins, the coordinatively unsaturated Ni(ii) ion in NiSOD is present in a surface-exposed loop region at the N-terminus, which might enable partial chelation. The results were consistent with the notion that the apo-DFOB-resin formed a ternary complex with NiSOD, which was not possible for either the coordinatively saturated Fe(iii)-DFOB-resin or the non-coordinating control resin systems. In support, ESI-TOF-MS measurements from a solution of a model Ni(ii)-SOD peptide and DFOB showed signals that correlated with a ternary Ni(ii)-SOD peptide-DFOB complex. Although any biological implications of a DFOB-NiSOD complex are unclear, the work shows that the metal coordination properties of siderophores might influence an array of metal-dependent biological processes beyond those established in iron uptake.
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Affiliation(s)
- Jenny Ni
- School of Medical Sciences, The University of Sydney New South Wales 2006 Australia
| | - James L Wood
- School of Medical Sciences, The University of Sydney New South Wales 2006 Australia
| | - Melanie Y White
- School of Medical Sciences, The University of Sydney New South Wales 2006 Australia
- Charles Perkins Centre, The University of Sydney New South Wales 2006 Australia
| | - Norbert Lihi
- ELKH-DE Mechanisms of Complex Homogeneous and Heterogeneous Chemical Reactions Research Group, Department of Inorganic and Analytical Chemistry, University of Debrecen Debrecen H-4032 Hungary
| | - Todd E Markham
- School of Medical Sciences, The University of Sydney New South Wales 2006 Australia
| | - Joseph Wang
- School of Medical Sciences, The University of Sydney New South Wales 2006 Australia
| | - Peter T Chivers
- Department of Chemistry, Durham University Durham DH1 3LE UK
- Department of Biosciences, Durham University Durham DH1 3LE UK
| | - Rachel Codd
- School of Medical Sciences, The University of Sydney New South Wales 2006 Australia
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Domergue J, Guinard P, Douillard M, Pécaut J, Hostachy S, Proux O, Lebrun C, Le Goff A, Maldivi P, Duboc C, Delangle P. A Series of Ni Complexes Based on a Versatile ATCUN-Like Tripeptide Scaffold to Decipher Key Parameters for Superoxide Dismutase Activity. Inorg Chem 2023. [PMID: 37247425 DOI: 10.1021/acs.inorgchem.3c00766] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The cellular level of reactive oxygen species (ROS) has to be controlled to avoid some pathologies, especially those linked to oxidative stress. One strategy for designing antioxidants consists of modeling natural enzymes involved in ROS degradation. Among them, nickel superoxide dismutase (NiSOD) catalyzes the dismutation of the superoxide radical anion, O2•-, into O2 and H2O2. We report here Ni complexes with tripeptides derived from the amino-terminal CuII- and NiII-binding (ATCUN) motif that mimics some structural features found in the active site of the NiSOD. A series of six mononuclear NiII complexes were investigated in water at physiological pH with different first coordination spheres, from compounds with a N3S to N2S2 set, and also complexes that are in equilibrium between the N-coordination (N3S) and S-coordination (N2S2). They were fully characterized by a combination of spectroscopic techniques, including 1H NMR, UV-vis, circular dichroism, and X-ray absorption spectroscopy, together with theoretical calculations and their redox properties studied by cyclic voltammetry. They all display SOD-like activity, with a kcat ranging between 0.5 and 2.0 × 106 M-1 s-1. The complexes in which the two coordination modes are in equilibrium are the most efficient, suggesting a beneficial effect of a nearby proton relay.
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Affiliation(s)
- Jérémy Domergue
- Univ. Grenoble Alpes, CNRS, DCM, 38000 Grenoble, France
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
| | - Pawel Guinard
- Univ. Grenoble Alpes, CNRS, DCM, 38000 Grenoble, France
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
| | - Magali Douillard
- Univ. Grenoble Alpes, CNRS, DCM, 38000 Grenoble, France
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
| | - Jacques Pécaut
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
| | - Sarah Hostachy
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
| | - Olivier Proux
- CNRS, OSUG, Université Grenoble Alpes, 38000 Grenoble, France
| | - Colette Lebrun
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
| | - Alan Le Goff
- Univ. Grenoble Alpes, CNRS, DCM, 38000 Grenoble, France
| | - Pascale Maldivi
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
| | - Carole Duboc
- Univ. Grenoble Alpes, CNRS, DCM, 38000 Grenoble, France
| | - Pascale Delangle
- IRIG, SyMMES, Univ. Grenoble Alpes, CEA, CNRS, Grenoble INP, 38000 Grenoble, France
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Functional Conversion of Acetyl-Coenzyme a Synthase to a Nickel Superoxide Dismutase via Rational Design of Coordination Microenvironment for the Ni d-Site. Int J Mol Sci 2022; 23:ijms23052652. [PMID: 35269794 PMCID: PMC8910529 DOI: 10.3390/ijms23052652] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Revised: 02/19/2022] [Accepted: 02/21/2022] [Indexed: 02/01/2023] Open
Abstract
The Nid site coordination microenvironment of a truncated acetyl-coenzyme A synthase has been designed systematically for functional conversion to a Ni-SOD-like enzyme. To this end, the first strategy is to introduce an axial histidine ligand, using mutations F598H, S594H and S594H-GP individually. The resulting three mutants obtained Ni-SOD-like activity successfully, although the catalytic activity was about 10-fold lower than in native Ni-SOD. The second strategy is to mimic the H-bond network in the second sphere coordination microenvironment of the native Ni-SOD. Two mutations based on F598H (EFG-F598H and YGP-F598H) were designed. The successful EFG-F598H exhibited ~3-fold Ni-SOD-like activity of F598H. These designed Ni-SOD-like metalloproteins were characterized by UV/Vis, EPR and Cyclic voltammetry while F598H was also characterized by X-ray protein crystallography. The pH titrations were performed to reveal the source of the two protons required for forming H2O2 in the SOD catalytic reaction. Based on all of the results, a proposed catalytic mechanism for the Ni-SOD-like metalloproteins is presented.
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Bonczidai-Kelemen D, Sciortino G, May NV, Garribba E, Fábián I, Lihi N. Introducing the penicillamine moiety into a metallopeptide mimicking the NiSOD enzyme: electronic and kinetic effects. Inorg Chem Front 2022. [DOI: 10.1039/d1qi01025e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The novel NiSOD related metallopeptide incorporates penicillamine moiety in the active center which alters both the electronic and kinetic features.
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Affiliation(s)
- Dóra Bonczidai-Kelemen
- Department of Inorganic and Analytical Chemistry, University of Debrecen, H-4032, Debrecen, Hungary
| | - Giuseppe Sciortino
- Institute of Chemical Research of Catalonia (ICIQ), The Barcelona Institute of Technology, 43007 Tarragona, Spain
| | - Nóra V. May
- Centre for Structural Science, Research Centre for Natural Sciences, H-1117, Budapest, Hungary
| | - Eugenio Garribba
- Dipartimento di Scienze Mediche, Chirurgiche e Sperimentali, Università di Sassari, I-07100 Sassari, Italy
| | - István Fábián
- Department of Inorganic and Analytical Chemistry, University of Debrecen, H-4032, Debrecen, Hungary
- MTA-DE Redox and Homogeneous Catalytic Reaction Mechanisms Research Group, University of Debrecen, H-4032, Debrecen, Hungary
| | - Norbert Lihi
- Department of Inorganic and Analytical Chemistry, University of Debrecen, H-4032, Debrecen, Hungary
- MTA-DE Redox and Homogeneous Catalytic Reaction Mechanisms Research Group, University of Debrecen, H-4032, Debrecen, Hungary
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7
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Kelemen D, May NV, Andrási M, Gáspár A, Fábián I, Lihi N. High Enzyme Activity of a Binuclear Nickel Complex Formed with the Binding Loops of the NiSOD Enzyme*. Chemistry 2020; 26:16767-16773. [PMID: 32744741 PMCID: PMC7756883 DOI: 10.1002/chem.202002706] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Indexed: 11/08/2022]
Abstract
Detailed equilibrium, spectroscopic and superoxide dismutase (SOD) activity studies are reported on a nickel complex formed with a new metallopeptide bearing two nickel binding loops of NiSOD. The metallopeptide exhibits unique nickel binding ability and the binuclear complex is a major species with 2×(NH2 ,Namide ,S- ,S- ) donor set even in an equimolar solution of the metal ion and the ligand. Nickel(III) species were generated by oxidizing the NiII complexes with KO2 and the coordination modes were identified by EPR spectroscopy. The binuclear complex formed with the binding motifs exhibits superior SOD activity, in this respect it is an excellent model of the native NiSOD enzyme. A detailed kinetic model is postulated that incorporates spontaneous decomposition of the superoxide ion, the dismutation cycle and fast redox degradation of the binuclear complex. The latter process leads to the elimination of the SOD activity. A unique feature of this system is that the NiIII form of the catalyst rapidly accumulates in the dismutation cycle and simultaneously the NiII form becomes a minor species.
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Affiliation(s)
- Dóra Kelemen
- Department of Inorganic and Analytical Chemistry, University of Debrecen, 4032, Debrecen, Hungary
| | - Nóra V May
- Research Centre for Natural Sciences, 1117, Budapest, Hungary
| | - Melinda Andrási
- Department of Inorganic and Analytical Chemistry, University of Debrecen, 4032, Debrecen, Hungary
| | - Attila Gáspár
- Department of Inorganic and Analytical Chemistry, University of Debrecen, 4032, Debrecen, Hungary
| | - István Fábián
- Department of Inorganic and Analytical Chemistry, University of Debrecen, 4032, Debrecen, Hungary.,MTA-DE Redox and Homogeneous Catalytic Reaction Mechanisms, Research Group, University of Debrecen, 4032, Debrecen, Hungary
| | - Norbert Lihi
- Department of Inorganic and Analytical Chemistry, University of Debrecen, 4032, Debrecen, Hungary.,MTA-DE Redox and Homogeneous Catalytic Reaction Mechanisms, Research Group, University of Debrecen, 4032, Debrecen, Hungary
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Domergue J, Pécaut J, Proux O, Lebrun C, Gateau C, Le Goff A, Maldivi P, Duboc C, Delangle P. Mononuclear Ni(II) Complexes with a S3O Coordination Sphere Based on a Tripodal Cysteine-Rich Ligand: pH Tuning of the Superoxide Dismutase Activity. Inorg Chem 2019; 58:12775-12785. [PMID: 31545024 DOI: 10.1021/acs.inorgchem.9b01686] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The superoxide dismutase (SOD) activity of mononuclear NiII complexes, whose structures are inspired by the NiSOD, has been investigated. They have been designed with a sulfur-rich pseudopeptide ligand, derived from nitrilotriacetic acid (NTA), where the three acid functions are grafted with cysteines (L3S). Two mononuclear complexes, which exist in pH-dependent proportions, have been fully characterized by a combination of spectroscopic techniques including 1H NMR, UV-vis, circular dichroism, and X-ray absorption spectroscopy, together with theoretical calculations. They display similar square-planar S3O coordination, with the three thiolates of the three cysteine moieties from L3S coordinated to the NiII ion, together with either a water molecule at physiological pH, as [NiL3S(OH2)]-, or a hydroxo ion in more basic conditions, as [NiL3S(OH)]2-. The 1H NMR study has revealed that contrary to the hydroxo ligand, the bound water molecule is labile. The cyclic voltammogram of both complexes displays an irreversible one-electron oxidation process assigned to the NiII/NiIII redox system with Epa = 0.48 and 0.31 V versus SCE for NiL3S(OH2) and NiL3S(OH), respectively. The SOD activity of both complexes has been tested. On the basis of the xanthine oxidase assay, an IC50 of about 1 μM has been measured at pH 7.4, where NiL3S(OH2) is mainly present (93% of the NiII species), while the IC50 is larger than 100 μM at pH 9.6, where NiL3S(OH) is the major species (92% of the NiII species). Interestingly, only NiL3S(OH2) displays SOD activity, suggesting that the presence of a labile ligand is required. The SOD activity has been also evaluated under catalytic conditions at pH 7.75, where the ratio between NiL3S(OH2)/ NiL3S(OH) is about (86:14), and a rate constant, kcat = 1.8 × 105 M-1 s-1, has been measured. NiL3S(OH2) is thus the first low-molecular weight, synthetic, bioinspired Ni complex that displays catalytic SOD activity in water at physiological pH, although it does not contain any N-donor ligand in its first coordination sphere, as in the NiSOD. Overall, the data show that a key structural feature is the presence of a labile ligand in the coordination sphere of the NiII ion.
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Affiliation(s)
- Jérémy Domergue
- Univ. Grenoble Alpes, CNRS, DCM , 38000 Grenoble , France.,Univ. Grenoble Alpes, CEA, CNRS, IRIG, SYMMES , 38000 Grenoble , France
| | - Jacques Pécaut
- Univ. Grenoble Alpes, CEA, CNRS, IRIG, SYMMES , 38000 Grenoble , France
| | - Olivier Proux
- Univ. Grenoble Alpes, CNRS, OSUG , 38000 Grenoble , France
| | - Colette Lebrun
- Univ. Grenoble Alpes, CEA, CNRS, IRIG, SYMMES , 38000 Grenoble , France
| | - Christelle Gateau
- Univ. Grenoble Alpes, CEA, CNRS, IRIG, SYMMES , 38000 Grenoble , France
| | - Alan Le Goff
- Univ. Grenoble Alpes, CNRS, DCM , 38000 Grenoble , France
| | - Pascale Maldivi
- Univ. Grenoble Alpes, CEA, CNRS, IRIG, SYMMES , 38000 Grenoble , France
| | - Carole Duboc
- Univ. Grenoble Alpes, CNRS, DCM , 38000 Grenoble , France
| | - Pascale Delangle
- Univ. Grenoble Alpes, CEA, CNRS, IRIG, SYMMES , 38000 Grenoble , France
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Selvan D, Prasad P, Farquhar ER, Shi Y, Crane S, Zhang Y, Chakraborty S. Redesign of a Copper Storage Protein into an Artificial Hydrogenase. ACS Catal 2019; 9:5847-5859. [PMID: 31341700 DOI: 10.1021/acscatal.9b00360] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
We report the construction of an artificial hydrogenase (ArH) by reengineering a Cu storage protein (Cspl) into a Ni-binding protein (NBP) employing rational metalloprotein design. The hypothesis driven design approach involved deleting existing Cu sites of Csp1 and identification of a target tetrathiolate Ni binding site within the protein scaffold followed by repacking the hydrophobic core. Guided by modeling, the NBP was expressed and purified in high purity. NBP is a well-folded and stable construct displaying native-like unfolding behavior. Spectroscopic and computational studies indicated that the NBP bound nickel in a distorted square planar geometry that validated the design. Ni(II)-NBP is active for photo-induced H2 evolution following a reductive quenching mechanism. Ni(II)-NBP catalyzed H+ reduction to H2 gas electrochemically as well. Analysis of the catalytic voltammograms established a proton-coupled electron transfer (PCET) mechanism. Electrolysis studies confirmed H2 evolution with quantitative Faradaic yields. Our studies demonstrate an important scope of rational metalloprotein design that allows imparting functions into protein scaffolds that have natively not evolved to possess the same function of the target metalloprotein constructs.
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Affiliation(s)
- Dhanashree Selvan
- Department of Chemistry and Biochemistry, University of Mississippi, University, Mississippi 38677, United States
| | - Pallavi Prasad
- Department of Chemistry and Biochemistry, University of Mississippi, University, Mississippi 38677, United States
| | - Erik R. Farquhar
- Case Western Reserve University Center for Synchrotron Biosciences, NSLS-II, Brookhaven National Laboratory, Upton, New York 11973, United States
| | - Yelu Shi
- Department of Chemistry and Chemical Biology, Stevens Institute of Technology, 1 Castle Point on Hudson, Hoboken, New Jersey 07030, United States
| | - Skyler Crane
- Department of Chemistry and Biochemistry, University of Mississippi, University, Mississippi 38677, United States
| | - Yong Zhang
- Department of Chemistry and Chemical Biology, Stevens Institute of Technology, 1 Castle Point on Hudson, Hoboken, New Jersey 07030, United States
| | - Saumen Chakraborty
- Department of Chemistry and Biochemistry, University of Mississippi, University, Mississippi 38677, United States
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Keegan BC, Ocampo D, Shearer J. pH Dependent Reversible Formation of a Binuclear Ni 2 Metal-Center Within a Peptide Scaffold. INORGANICS 2019; 7:90. [PMID: 38046130 PMCID: PMC10691859 DOI: 10.3390/inorganics7070090] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2023] Open
Abstract
A disulfide-bridged peptide containing two Ni2+ binding sites based on the nickel superoxide dismutase protein, {Ni2(SODmds)}, has been prepared. At physiological pH (7.4) it was found that the metal sites are mononuclear with a square planar NOS2 coordination environment with the two sulfur-based ligands derived from cysteinate residues, the nitrogen ligand derived from the amide backbone and a water ligand. Furthermore, S K-edge X-ray absorption spectroscopy indicated that the two cysteinate sulfur atoms ligated to nickel are each protonated. Elevation of the pH to 9.6 results in the deprotonation of the cysteinate sulfur atoms, and yields a binuclear, cysteinate bridged Ni22+ center with each nickel contained in a distorted square planar geometry. At both pH = 7.4 and 9.6 the nickel sites are moderately air sensitive, yielding intractable oxidation products. However, at pH = 9.6 {Ni2(SODmds)} reacts with O2 at an ~3.5-fold faster rate than at pH = 7.4. Electronic structure calculations indicate the reduced reactivity at pH = 7.4 is a result of a reduction in S(3p) character and deactivation of the nucleophilic frontier molecular orbitals upon cysteinate sulfur protonation.
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Affiliation(s)
- Brenna C. Keegan
- Department of Chemistry, Trinity University, 1 Trinity Place, San Antonio, TX 78212, U.S.A
| | - Daniel Ocampo
- Department of Chemistry, Trinity University, 1 Trinity Place, San Antonio, TX 78212, U.S.A
| | - Jason Shearer
- Department of Chemistry, Trinity University, 1 Trinity Place, San Antonio, TX 78212, U.S.A
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Lihi N, Csire G, Szakács B, May NV, Várnagy K, Sóvágó I, Fábián I. Stabilization of the Nickel Binding Loop in NiSOD and Related Model Complexes: Thermodynamic and Structural Features. Inorg Chem 2019; 58:1414-1424. [DOI: 10.1021/acs.inorgchem.8b02952] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Norbert Lihi
- MTA-DE Redox and Homogeneous Catalytic Reaction Mechanisms Research Group, University of Debrecen, H-4032 Debrecen, Hungary
- Department of Inorganic and Analytical Chemistry, University of Debrecen, H-4032 Debrecen, Hungary
| | - Gizella Csire
- Department of Inorganic and Analytical Chemistry, University of Debrecen, H-4032 Debrecen, Hungary
| | - Bence Szakács
- Department of Inorganic and Analytical Chemistry, University of Debrecen, H-4032 Debrecen, Hungary
| | - Nóra V. May
- Research Centre of Natural Sciences, Hungarian Academy of Sciences, H-1117 Budapest, Hungary
| | - Katalin Várnagy
- Department of Inorganic and Analytical Chemistry, University of Debrecen, H-4032 Debrecen, Hungary
| | - Imre Sóvágó
- Department of Inorganic and Analytical Chemistry, University of Debrecen, H-4032 Debrecen, Hungary
| | - István Fábián
- MTA-DE Redox and Homogeneous Catalytic Reaction Mechanisms Research Group, University of Debrecen, H-4032 Debrecen, Hungary
- Department of Inorganic and Analytical Chemistry, University of Debrecen, H-4032 Debrecen, Hungary
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12
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Tietze D, Sartorius J, Koley Seth B, Herr K, Heimer P, Imhof D, Mollenhauer D, Buntkowsky G. New insights into the mechanism of nickel superoxide degradation from studies of model peptides. Sci Rep 2017; 7:17194. [PMID: 29222438 PMCID: PMC5722923 DOI: 10.1038/s41598-017-17446-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Accepted: 11/27/2017] [Indexed: 12/27/2022] Open
Abstract
A series of small, catalytically active metallopeptides, which were derived from the nickel superoxide dismutase (NiSOD) active site were employed to study the mechanism of superoxide degradation especially focusing on the role of the axial imidazole ligand. In the literature, there are contradicting propositions about the catalytic importance of the N-terminal histidine. Therefore, we studied the stability and activity of a set of eight NiSOD model peptides, which represent the major model systems discussed in the literature to date, yet differing in their length and their Ni-coordination. UV-Vis-coupled stopped-flow kinetic measurements and mass spectrometry analysis unveiled their high oxidation sensitivity in the presence of oxygen and superoxide resulting into a much faster Ni(II)-peptide degradation for the amine/amide Ni(II) coordination than for the catalytically inactive bis-amidate Ni(II) coordination. With respect to these results we determined the catalytic activities for all NiSOD mimics studied herein, which turned out to be in almost the same range of about 2 × 106 M-1 s-1. From these experiments, we concluded that the amine/amide Ni(II) coordination is clearly the key factor for catalytic activity. Finally, we were able to clarify the role of the N-terminal histidine and to resolve the contradictory literature propositions, reported in previous studies.
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Affiliation(s)
- Daniel Tietze
- Eduard-Zintl Institute for Physical and Inorganic Chemistry, Darmstadt University of Technology, Alarich-Weiss-Str. 8, 64287, Darmstadt, Germany.
| | - Jana Sartorius
- Eduard-Zintl Institute for Physical and Inorganic Chemistry, Darmstadt University of Technology, Alarich-Weiss-Str. 8, 64287, Darmstadt, Germany
| | - Banabithi Koley Seth
- Eduard-Zintl Institute for Physical and Inorganic Chemistry, Darmstadt University of Technology, Alarich-Weiss-Str. 8, 64287, Darmstadt, Germany
| | - Kevin Herr
- Eduard-Zintl Institute for Physical and Inorganic Chemistry, Darmstadt University of Technology, Alarich-Weiss-Str. 8, 64287, Darmstadt, Germany
| | - Pascal Heimer
- Pharmaceutical Biochemistry and Bioanalytics, Pharmaceutical Institute, University of Bonn, An der Immenburg 4, D-53119, Bonn, Germany
| | - Diana Imhof
- Pharmaceutical Biochemistry and Bioanalytics, Pharmaceutical Institute, University of Bonn, An der Immenburg 4, D-53119, Bonn, Germany
| | - Doreen Mollenhauer
- Institute of Physical Chemistry, Justus Liebig University Giessen, Heinrich-Buff-Ring 17, D-35392, Giessen, Germany
| | - Gerd Buntkowsky
- Eduard-Zintl Institute for Physical and Inorganic Chemistry, Darmstadt University of Technology, Alarich-Weiss-Str. 8, 64287, Darmstadt, Germany.
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13
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Truong PT, Gale EM, Dzul SP, Stemmler TL, Harrop TC. Steric Enforcement about One Thiolate Donor Leads to New Oxidation Chemistry in a NiSOD Model Complex. Inorg Chem 2017; 56:7761-7780. [PMID: 28459242 DOI: 10.1021/acs.inorgchem.7b00485] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Ni-containing superoxide dismutase (NiSOD) represents an unusual member of the SOD family due to the presence of oxygen-sensitive Ni-SCys bonds at its active site. Reported in this account is the synthesis and properties of the NiII complex of the N3S2 ligand [N3S2Me2]3- ([N3S2Me2]3- = deprotonated form of 2-((2-mercapto-2-methylpropyl)(pyridin-2-ylmethyl)amino)-N-(2-mercaptoethyl)acetamide), namely Na[Ni(N3S2Me2)] (2), as a NiSOD model that features sterically robust gem-(CH3)2 groups on the thiolate α-C positioned trans to the carboxamide. The crystal structure of 2, coupled with spectroscopic measurements from 1H NMR, X-ray absorption, IR, UV-vis, and mass spectrometry (MS), reveal a planar NiII (S = 0) ion coordinated by only the N2S2 basal donors of the N3S2 ligand. While the structure and spectroscopic properties of 2 resemble those of NiSODred and other models, the asymmetric S ligands open up new reaction paths upon chemical oxidation. One unusual oxidation product is the planar NiII-N3S complex [Ni(Lox)] (5; Lox = 2-(5,5-dimethyl-2-(pyridin-2-yl)thiazolidin-3-yl)-N-(2-mercaptoethyl)acetamide), where two-electron oxidation takes place at the substituted thiolate and py-CH2 carbon to generate a thiazolidine heterocycle. Electrochemical measurements of 2 reveal irreversible events wholly consistent with thiolate redox, which were identified by comparison to the ZnII complex Na[Zn(N3S2Me2)] (3). Although no reaction is observed between 2 and azide, reaction of 2 with superoxide produces multiple products on the basis of UV-vis and MS data, one of which is 5. Density functional theory (DFT) computations suggest that the HOMO in 2 is π* with primary contributions from Ni-dπ/S-pπ orbitals. These contributions can be modulated and biased toward Ni when electron-withdrawing groups are placed on the thiolate α-C. Analysis of the oxidized five-coordinate species 2ox* by DFT reveal a singly occupied spin-up (α) MO that is largely thiolate based, which supports the proposed NiIII-thiolate/NiII-thiyl radical intermediates that ultimately yield 5 and other products.
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Affiliation(s)
- Phan T Truong
- Department of Chemistry and Center for Metalloenzyme Studies, The University of Georgia , 140 Cedar Street, Athens, Georgia 30602, United States
| | - Eric M Gale
- Department of Chemistry and Center for Metalloenzyme Studies, The University of Georgia , 140 Cedar Street, Athens, Georgia 30602, United States
| | - Stephen P Dzul
- Departments of Pharmaceutical Sciences, Biochemistry and Molecular Biology, Wayne State University , Detroit, Michigan 48201, United States
| | - Timothy L Stemmler
- Departments of Pharmaceutical Sciences, Biochemistry and Molecular Biology, Wayne State University , Detroit, Michigan 48201, United States
| | - Todd C Harrop
- Department of Chemistry and Center for Metalloenzyme Studies, The University of Georgia , 140 Cedar Street, Athens, Georgia 30602, United States
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14
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Campeciño JO, Maroney MJ. Reinventing the Wheel: The NiSOD Story. THE BIOLOGICAL CHEMISTRY OF NICKEL 2017. [DOI: 10.1039/9781788010580-00170] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The most recently discovered SOD requires nickel in its active site – NiSOD. Among the available metals, nickel seems an unlikely redox center. This chapter discusses the protein adaptations required in order to use nickel for SOD catalysis. Cysteine ligands are employed for the first time in an SOD, to suppress the potential of the Ni(ii/iii) couple. However, this adaptation alone is not sufficient to produce an SOD, since thiolate ligands are sensitive to oxidation by H2O2 and O2. Additional adaptations include the use of two unusual backbone N-donor ligands, an amidate and the N-terminal amine. Yet merely producing a stable Ni redox center is not sufficient for SOD catalysis. A source of protons is needed to produce H2O2 and the pH-independent catalysis that is characteristic of SODs. Thus, the cysteine thiolates were also employed to provide a site for protonation. In restricting active site access, NiSOD appears to have utilized the same strategy employed by MnSOD and FeSOD – a “gateway” formed by Tyr residues. Thus, NiSOD represents evolution that converged on the same criteria for catalysis as other SODs, where the adaptations to the metal site are uniquely suited to using nickel as a redox center.
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Affiliation(s)
| | - Michael J. Maroney
- Department of Chemistry, University of Massachusetts Amherst MA 01003 USA
- Program in Molecular and Cellular Biology, University of Massachusetts Amherst MA 01003 USA
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15
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Steiner RA, Dzul SP, Stemmler TL, Harrop TC. Synthesis and Speciation-Dependent Properties of a Multimetallic Model Complex of NiSOD That Exhibits Unique Hydrogen-Bonding. Inorg Chem 2017; 56:2849-2862. [PMID: 28212040 DOI: 10.1021/acs.inorgchem.6b02997] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The complex Na3[{NiII(nmp)}3S3BTAalk)] (1) (nmp2- = deprotonated form of N-(2-mercaptoethyl)picolinamide; H3S3BTAalk = N1,N3,N5-tris(2-mercaptoethyl)benzene-1,3,5-tricarboxamide, where H = dissociable protons), supported by the thiolate-benzenetricarboxamide scaffold (S3BTAalk), has been synthesized as a trimetallic model of nickel-containing superoxide dismutase (NiSOD). X-ray absorption spectroscopy (XAS) and 1H NMR measurements on 1 indicate that the NiII centers are square-planar with N2S2 coordination, and Ni-N and Ni-S distances of 1.95 and 2.16 Å, respectively. Additional evidence from IR indicates the presence of H-bonds in 1 from the approximately -200 cm-1 shift in νNH from free ligand. The presence of H-bonds allows for speciation that is temperature-, concentration-, and solvent-dependent. In unbuffered water and at low temperature, a dimeric complex (1A; λ = 410 nm) that aggregates through intermolecular NH···O═C bonds of BTA units is observed. Dissolution of 1 in pH 7.4 buffer or in unbuffered water at temperatures above 50 °C results in monomeric complex (1M; λ = 367 nm) linked through intramolecular NH···S bonds. DFT computations indicate a low energy barrier between 1A and 1M with nearly identical frontier MOs and Ni-ligand metrics. Notably, 1A and 1M exhibit remarkable stability in protic solvents such as MeOH and H2O, in stark contrast to monometallic [NiII(nmp)(SR)]- complexes. The reactivity of 1 with excess O2, H2O2, and O2•- is species-dependent. IR and UV-vis reveal that 1A in MeOH reacts with excess O2 to yield an S-bound sulfinate, but does not react with O2•-. In contrast, 1M is stable to O2 in pH 7.4 buffer, but reacts with O2•- to yield a putative [NiII(nmp)(O2)]- complex from release of the BTA-thiolate based on EPR.
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Affiliation(s)
- Ramsey A Steiner
- Department of Chemistry and Center for Metalloenzyme Studies, The University of Georgia , 140 Cedar St, Athens, Georgia 30602, United States
| | - Stephen P Dzul
- Departments of Pharmaceutical Sciences, and Biochemistry and Molecular Biology, Wayne State University , Detroit, Michigan 48201, United States
| | - Timothy L Stemmler
- Departments of Pharmaceutical Sciences, and Biochemistry and Molecular Biology, Wayne State University , Detroit, Michigan 48201, United States
| | - Todd C Harrop
- Department of Chemistry and Center for Metalloenzyme Studies, The University of Georgia , 140 Cedar St, Athens, Georgia 30602, United States
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16
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Alfurayj IA, Young VG, Jensen MP. Structural Characterization of Thermochromic and Spin Equilibria in Solid-State Ni(detu)4Cl2 (detu = N,N'-Diethylthiourea). Inorg Chem 2016; 55:1469-79. [PMID: 26836378 DOI: 10.1021/acs.inorgchem.5b02203] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Consecutive thermochromic lattice distortional and spin crossover equilibria in solid-state Ni(detu)4Cl2 (detu = N,N'-diethylthiourea) are investigated by variable-temperature X-ray crystallography (173-333 K), DFT calculations, and differential scanning calorimetry. Thermochromism and anomalous magnetism were reported previously (S. L. Holt, Jr., et al. J. Am. Chem. Soc. 1964, 86, 519-520); the latter was attributed to equilibration of a singlet ground state and a thermally accessible triplet state, but structural data were not obtained. A crystal structure at 173(2) K revealed [Ni(detu)4](2+) centers with distorted planar ligation of nickel(II) to the four sulfur atoms, with an average Ni-S bond length of 2.226(3) Å. The nickel ion was displaced out-of-plane by 0.334 Å toward a proximal apical chloride at a nonbonding distance of 3.134(1) Å. Asymmetry in the trans S-Ni-S angles was coupled to a monoclinic ↔ tetragonal lattice distortion (T(1/2) = 254 ± 11 K), resulting in thermochromism. Spin crossover occurs by tetragonal modulation of nickel(II) with approach of the proximal chloride at higher temperatures (T(1/2) = 383 ± 18 K), which is consistent with a contraction of -0.096(4) Å in the Ni···Cl separation observed at 293 K. A high-spin (S = 1) square-pyramidal [Ni(dmtu)4Cl](+) model (dmtu = N,N'-dimethylthiourea) was optimized by DFT calculations, which estimated limiting equatorial Ni-S bond lengths of 2.45 Å and an apical Ni-Cl bond of 2.43 Å. Electronic spectra of the spin isomers were calculated by TD-DFT methods. Assignment of the FTIR spectrum was assisted by frequency calculations and isotope substitution.
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Affiliation(s)
- Ibrahim A Alfurayj
- Department of Chemistry and Biochemistry, Ohio University , Athens, Ohio 45701, United States
| | - Victor G Young
- X-ray Crystallographic Facility, Department of Chemistry, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Michael P Jensen
- Department of Chemistry and Biochemistry, Ohio University , Athens, Ohio 45701, United States
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17
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Campeciño JO, Dudycz LW, Tumelty D, Berg V, Cabelli DE, Maroney MJ. A Semisynthetic Strategy Leads to Alteration of the Backbone Amidate Ligand in the NiSOD Active Site. J Am Chem Soc 2015; 137:9044-52. [PMID: 26135142 DOI: 10.1021/jacs.5b03629] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Computational investigations have implicated the amidate ligand in nickel superoxide dismutase (NiSOD) in stabilizing Ni-centered redox catalysis and in preventing cysteine thiolate ligand oxidation. To test these predictions, we have used an experimental approach utilizing a semisynthetic scheme that employs native chemical ligation of a pentapeptide (HCDLP) to recombinant S. coelicolor NiSOD lacking these N-terminal residues, NΔ5-NiSOD. Wild-type enzyme produced in this manner exhibits the characteristic spectral properties of recombinant WT-NiSOD and is as catalytically active. The semisynthetic scheme was also employed to construct a variant where the amidate ligand was converted to a secondary amine, H1*-NiSOD, a novel strategy that retains a backbone N-donor atom. The H1*-NiSOD variant was found to have only ∼1% of the catalytic activity of the recombinant wild-type enzyme, and had altered spectroscopic properties. X-ray absorption spectroscopy reveals a four-coordinate planar site with N2S2-donor ligands, consistent with electronic absorption spectroscopic results indicating that the Ni center in H1*-NiSOD is mostly reduced in the as-isolated sample, as opposed to 50:50 Ni(II)/Ni(III) mixture that is typical for the recombinant wild-type enzyme. The EPR spectrum of as-isolated H1*-NiSOD accounts for ∼11% of the Ni in the sample and is similar to WT-NiSOD, but more axial, with gz < gx,y. (14)N-hyperfine is observed on gz, confirming the addition of the apical histidine ligand in the Ni(III) complex. The altered electronic properties and implications for redox catalysis are discussed in light of predictions based on synthetic and computational models.
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Affiliation(s)
- Julius O Campeciño
- †Department of Chemistry University of Massachusetts, Amherst, Massachusetts 01003, United States
| | - Lech W Dudycz
- ‡Lex Company Research Lab, Phoenix Park, 2 Shaker Road, Suite D 106, Shirley, Massachusetts 01464, United States
| | - David Tumelty
- §New England Peptide, 65 Zub Lane, Gardner, Massachusetts 01440, United States
| | - Volker Berg
- †Department of Chemistry University of Massachusetts, Amherst, Massachusetts 01003, United States
| | - Diane E Cabelli
- ∥Department of Chemistry, Brookhaven National Laboratory, Building 555A, P.O. Box 5000 Upton, New York 11973, United States
| | - Michael J Maroney
- †Department of Chemistry University of Massachusetts, Amherst, Massachusetts 01003, United States
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18
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Broering EP, Dillon S, Gale EM, Steiner RA, Telser J, Brunold TC, Harrop TC. Accessing Ni(III)-thiolate versus Ni(II)-thiyl bonding in a family of Ni-N2S2 synthetic models of NiSOD. Inorg Chem 2015; 54:3815-28. [PMID: 25835183 PMCID: PMC4630978 DOI: 10.1021/ic503124f] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Superoxide dismutase (SOD) catalyzes the disproportionation of superoxide (O2(• -)) into H2O2 and O2(g) by toggling through different oxidation states of a first-row transition metal ion at its active site. Ni-containing SODs (NiSODs) are a distinct class of this family of metalloenzymes due to the unusual coordination sphere that is comprised of mixed N/S-ligands from peptide-N and cysteine-S donor atoms. A central goal of our research is to understand the factors that govern reactive oxygen species (ROS) stability of the Ni-S(Cys) bond in NiSOD utilizing a synthetic model approach. In light of the reactivity of metal-coordinated thiolates to ROS, several hypotheses have been proffered and include the coordination of His1-Nδ to the Ni(II) and Ni(III) forms of NiSOD, as well as hydrogen bonding or full protonation of a coordinated S(Cys). In this work, we present NiSOD analogues of the general formula [Ni(N2S)(SR')](-), providing a variable location (SR' = aryl thiolate) in the N2S2 basal plane coordination sphere where we have introduced o-amino and/or electron-withdrawing groups to intercept an oxidized Ni species. The synthesis, structure, and properties of the NiSOD model complexes (Et4N)[Ni(nmp)(SPh-o-NH2)] (2), (Et4N)[Ni(nmp)(SPh-o-NH2-p-CF3)] (3), (Et4N)[Ni(nmp)(SPh-p-NH2)] (4), and (Et4N)[Ni(nmp)(SPh-p-CF3)] (5) (nmp(2-) = dianion of N-(2-mercaptoethyl)picolinamide) are reported. NiSOD model complexes with amino groups positioned ortho to the aryl-S in SR' (2 and 3) afford oxidized species (2(ox) and 3(ox)) that are best described as a resonance hybrid between Ni(III)-SR and Ni(II)-(•)SR based on ultraviolet-visible (UV-vis), magnetic circular dichroism (MCD), and electron paramagnetic resonance (EPR) spectroscopies, as well as density functional theory (DFT) calculations. The results presented here, demonstrating the high percentage of S(3p) character in the highest occupied molecular orbital (HOMO) of the four-coordinate reduced form of NiSOD (NiSODred), suggest that the transition from NiSODred to the five-coordinate oxidized form of NiSOD (NiSODox) may go through a four-coordinate Ni-(•)S(Cys) (NiSODox-Hisoff) that is stabilized by coordination to Ni(II).
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Affiliation(s)
- Ellen P. Broering
- Department of Chemistry and Center for Metalloenzyme Studies, The University of Georgia, 1001 Cedar Street, Athens, Georgia 30602, United States
| | - Stephanie Dillon
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States
| | - Eric M. Gale
- Department of Chemistry and Center for Metalloenzyme Studies, The University of Georgia, 1001 Cedar Street, Athens, Georgia 30602, United States
| | - Ramsey A. Steiner
- Department of Chemistry and Center for Metalloenzyme Studies, The University of Georgia, 1001 Cedar Street, Athens, Georgia 30602, United States
| | - Joshua Telser
- Department of Biological, Chemical and Physical Sciences, Roosevelt University, 430 South Michigan Avenue, Chicago, Illinois 60605, United States
| | - Thomas C. Brunold
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States
| | - Todd C. Harrop
- Department of Chemistry and Center for Metalloenzyme Studies, The University of Georgia, 1001 Cedar Street, Athens, Georgia 30602, United States
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19
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Shearer J, Schmitt JC, Clewett HS. Adiabaticity of the Proton-Coupled Electron-Transfer Step in the Reduction of Superoxide Effected by Nickel-Containing Superoxide Dismutase Metallopeptide-Based Mimics. J Phys Chem B 2015; 119:5453-61. [DOI: 10.1021/acs.jpcb.5b02640] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jason Shearer
- Department of Chemistry, University of Nevada, 1664 North Virginia Street, Reno, Nevada 89557, United States
| | - Jennifer C. Schmitt
- Department of Chemistry, University of Nevada, 1664 North Virginia Street, Reno, Nevada 89557, United States
| | - Heather S. Clewett
- Department of Chemistry, University of Nevada, 1664 North Virginia Street, Reno, Nevada 89557, United States
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20
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Lin C, Yu W, Yao J, Wang B, Liu Z, Zhang Y. Nickel-Catalyzed Direct Thioetherification of β-C(sp3)–H Bonds of Aliphatic Amides. Org Lett 2015; 17:1340-3. [DOI: 10.1021/acs.orglett.5b00471] [Citation(s) in RCA: 100] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Cong Lin
- Department
of Chemistry, Zhejiang University, Hangzhou 310027, China
| | - Wenlong Yu
- Department
of Chemistry, Zhejiang University, Hangzhou 310027, China
| | - Jinzhong Yao
- Department
of Chemistry, Zhejiang University, Hangzhou 310027, China
| | - Bingjie Wang
- Department
of Chemistry, Zhejiang University, Hangzhou 310027, China
| | - Zhanxiang Liu
- Department
of Chemistry, Zhejiang University, Hangzhou 310027, China
| | - Yuhong Zhang
- Department
of Chemistry, Zhejiang University, Hangzhou 310027, China
- State
Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, China
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21
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Ryan KC, Guce AI, Johnson OE, Brunold TC, Cabelli DE, Garman SC, Maroney MJ. Nickel superoxide dismutase: structural and functional roles of His1 and its H-bonding network. Biochemistry 2015; 54:1016-27. [PMID: 25580509 DOI: 10.1021/bi501258u] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Crystal structures of nickel-dependent superoxide dismutases (NiSODs) reveal the presence of a H-bonding network formed between the NH group of the apical imidazole ligand from His1 and the Glu17 carboxylate from a neighboring subunit in the hexameric enzyme. This interaction is supported by another intrasubunit H-bond between Glu17 and Arg47. In this study, four mutant NiSOD proteins were produced to experimentally evaluate the roles of this H-bonding network and compare the results with prior predictions from density functional theory calculations. The X-ray crystal structure of H1A-NiSOD, which lacks the apical ligand entirely, reveals that in the absence of the Glu17-His1 H-bond, the active site is disordered. Characterization of this variant using X-ray absorption spectroscopy (XAS) shows that Ni(II) is bound in the expected N2S2 planar coordination site. Despite these structural perturbations, the H1A-NiSOD variant retains 4% of wild-type (WT) NiSOD activity. Three other mutations were designed to preserve the apical imidazole ligand but perturb the H-bonding network: R47A-NiSOD, which lacks the intramolecular H-bonding interaction; E17R/R47A-NiSOD, which retains the intramolecular H-bond but lacks the intermolecular Glu17-His1 H-bond; and E17A/R47A-NiSOD, which lacks both H-bonding interactions. These variants were characterized by a combination of techniques, including XAS to probe the nickel site structure, kinetic studies employing pulse-radiolytic production of superoxide, and electron paramagnetic resonance to assess the Ni redox activity. The results indicate that in addition to the roles in redox tuning suggested on the basis of previous computational studies, the Glu17-His1 H-bond plays an important structural role in the proper folding of the "Ni-hook" motif that is a critical feature of the active site.
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Affiliation(s)
- Kelly C Ryan
- Department of Chemistry, University of Massachusetts at Amherst , 104 Lederle Graduate Research Tower A, 710 North Pleasant Street, Amherst, Massachusetts 01003, United States
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22
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Shearer J, Peck KL, Schmitt JC, Neupane KP. Cysteinate protonation and water hydrogen bonding at the active-site of a nickel superoxide dismutase metallopeptide-based mimic: implications for the mechanism of superoxide reduction. J Am Chem Soc 2014; 136:16009-22. [PMID: 25322331 DOI: 10.1021/ja5079514] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Nickel-containing superoxide dismutase (NiSOD) is a mononuclear cysteinate-ligated nickel metalloenzyme that catalyzes the disproportionation of superoxide into dioxygen and hydrogen peroxide by cycling between Ni(II) and Ni(III) oxidation states. All of the ligating residues to nickel are found within the first six residues from the N-terminus, which has prompted several research groups to generate NiSOD metallopeptide-based mimics derived from the first several residues of the NiSOD sequence. To assess the viability of using these metallopeptide-based mimics (NiSOD maquettes) to probe the mechanism of SOD catalysis facilitated by NiSOD, we computationally explored the initial step of the O2(-) reduction mechanism catalyzed by the NiSOD maquette {Ni(II)(SOD(m1))} (SOD(m1) = HCDLP CGVYD PA). Herein we use spectroscopic (S K-edge X-ray absorption spectroscopy, electronic absorption spectroscopy, and circular dichroism spectroscopy) and computational techniques to derive the detailed active-site structure of {Ni(II)(SOD(m1))}. These studies suggest that the {Ni(II)(SOD(m1))} active-site possesses a Ni(II)-S(H(+))-Cys(6) moiety and at least one associated water molecule contained in a hydrogen-bonding interaction to the coordinated Cys(2) and Cys(6) sulfur atoms. A computationally derived mechanism for O2(-) reduction using the formulated active-site structure of {Ni(II)(SOD(m1))} suggests that O2(-) reduction takes place through an apparent initial outersphere hydrogen atom transfer (HAT) from the Ni(II)-S(H(+))-Cys(6) moiety to the O2(-) molecule. It is proposed that the water molecule aids in driving the reaction forward by lowering the Ni(II)-S(H(+))-Cys(6) pK(a). Such a mechanism is not possible in NiSOD itself for structural reasons. These results therefore strongly suggest that maquettes derived from the primary sequence of NiSOD are mechanistically distinct from NiSOD itself despite the similarities in the structure and physical properties of the metalloenzyme vs the NiSOD metallopeptide-based models.
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Affiliation(s)
- Jason Shearer
- Department of Chemistry, University of Nevada, Reno , Reno, Nevada 89557, United States
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23
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Dołęga A, Jabłońska A, Pladzyk A, Ponikiewski Ł, Ferenc W, Sarzyński J, Herman A. Synthesis and characterization of mononuclear Zn(II), Co(II) and Ni(II) complexes containing a sterically demanding silanethiolate ligand derived from tris(2,6-diisopropylphenoxy)silanethiol. Dalton Trans 2014; 43:12766-75. [PMID: 25014574 DOI: 10.1039/c4dt01079e] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Four heteroleptic complexes of nickel(ii), cobalt(ii) and zinc(ii), containing a monodentate silanethiolate ligand derived from tris(2,6-diisopropylphenoxy)silanethiol (TDST), were prepared and characterized. Nickel(ii) and cobalt(ii) complexes of the formula M(NH3)2(TDST)2 (M = Ni(ii) complex , M = Co(ii) complex ) were obtained from the respective chlorides. Zinc complexes of the general formula Zn(acac)(TDST)(L), where L = EtOH (complex ) or H2O (complex ), were obtained from zinc acetylacetonate. A single-crystal X-ray structural analysis revealed that all crystalline products are solvent adducts. The geometries of ligands in the complexes are typical: distorted tetrahedral in zinc and cobalt(ii) complexes and square planar in nickel(ii) compounds. Magnetic studies performed for Ni(ii) and Co(ii) compounds confirmed the diamagnetic character of the first complex and high-spin paramagnetic configuration of the latter. Nickel(ii) and cobalt(ii) complexes were additionally characterized by UV-Vis and IR spectroscopy. IR bands for ligands in the complexes were assigned with the help of the DFT vibrational frequency calculations.
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Affiliation(s)
- Anna Dołęga
- Department of Inorganic Chemistry, Chemical Faculty, Gdansk University of Technology, G. Narutowicza St. 11/12, 80-233 Gdansk, Poland.
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Shearer J. Insight into the structure and mechanism of nickel-containing superoxide dismutase derived from peptide-based mimics. Acc Chem Res 2014; 47:2332-41. [PMID: 24825124 DOI: 10.1021/ar500060s] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Nickel superoxide dismutase (NiSOD) is a nickel-containing metalloenzyme that catalyzes the disproportionation of superoxide through a ping-pong mechanism that relies on accessing reduced Ni(II) and oxidized Ni(III) oxidation states. NiSOD is the most recently discovered SOD. Unlike the other known SODs (MnSOD, FeSOD, and (CuZn)SOD), which utilize "typical" biological nitrogen and oxygen donors, NiSOD utilizes a rather unexpected ligand set. In the reduced Ni(II) oxidation state, NiSOD utilizes nitrogen ligands derived from the N-terminal amine and an amidate along with two cysteinates sulfur donors. These are unusual biological ligands, especially for an SOD: amine and amidate donors are underrepresented as biological ligands, whereas cysteinates are highly susceptible to oxidative damage. An axial histidine imidazole binds to nickel upon oxidation to Ni(III). This bond is long (2.3-2.6 Å) owing to a tight hydrogen-bonding network. All of the ligating residues to Ni(II) and Ni(III) are found within the first 6 residues from the NiSOD N-terminus. Thus, small nickel-containing metallopeptides derived from the first 6-12 residues of the NiSOD sequence can reproduce many of the properties of NiSOD itself. Using these nickel-containing metallopeptide-based NiSOD mimics, we have shown that the minimal sequence needed for nickel binding and reproduction of the structural, spectroscopic, and functional properties of NiSOD is H2N-HCXXPC. Insight into how NiSOD avoids oxidative damage has also been gained. Using small NiN2S2 complexes and metallopeptide-based mimics, it was shown that the unusual nitrogen donor atoms protect the cysteinates from oxidative damage (both one-electron oxidation and oxygen atom insertion reactions) by fine-tuning the electronic structure of the nickel center. Changing the nitrogen donor set to a bis-amidate or bis-amine nitrogen donor led to catalytically nonviable species owing to nickel-cysteinate bond oxidative damage. Only the amine/amidate nitrogen donor atoms within the NiSOD ligand set produce a catalytically viable species. These metallopeptide-based mimics have also hinted at the detailed mechanism of SOD catalysis by NiSOD. One such aspect is that the axial imidazole likely remains ligated to the Ni center under rapid catalytic conditions (i.e., high superoxide loads). This reduces the degree of structural rearrangement about the nickel center, leading to higher catalytic rates. Metallopeptide-based mimics have also shown that, although an axial ligand to Ni(III) is required for catalysis, the rates are highest when this is a weak interaction, suggesting a reason for the long axial His-Ni(III) bond found in NiSOD. These mimics have also suggested a surprising mechanistic insight: O2(-) reduction via a "H(•)" tunneling event from a R-S(H(+))-Ni(II) moiety to O2(-) is possible. The importance of this mechanism in NiSOD has not been verified.
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Affiliation(s)
- Jason Shearer
- Department
of Chemistry, University of Nevada, Reno, Reno, Nevada 89557, United States
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25
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Chatterjee SK, Maji RC, Barman SK, Olmstead MM, Patra AK. Hexacoordinate nickel(II)/(III) complexes that mimic the catalytic cycle of nickel superoxide dismutase. Angew Chem Int Ed Engl 2014; 53:10184-9. [PMID: 25056843 DOI: 10.1002/anie.201404133] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2014] [Revised: 06/03/2014] [Indexed: 11/07/2022]
Abstract
A functional model complex of nickel superoxide dismutase (NiSOD) with a non-peptide ligand which mimics the full catalytic cycle of NiSOD is unknown. Similarly, it has not been fully elucidated whether NiSOD activity is a result of an outer- or inner-sphere electron-transfer mechanism. With this in mind, two octahedral nickel(II)/(III) complexes of a bis-tridentate N2 S donor carboxamide ligand, N-2-phenylthiophenyl-2'-pyridinecarboxamide (HL(Ph)), have been synthesized, structurally characterized, and their SOD activities examined. These complexes mimic the full catalytic cycle of NiSOD. Electrochemical experiments support an outer-sphere electron-transfer mechanism for their SOD activity.
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Affiliation(s)
- Sudip K Chatterjee
- Department of Chemistry, National Institute of Technology Durgapur, Mahatma Gandhi Avenue, Durgapur 713 209 (WB) (India)
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26
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Chatterjee SK, Maji RC, Barman SK, Olmstead MM, Patra AK. Hexacoordinate Nickel(II)/(III) Complexes that Mimic the Catalytic Cycle of Nickel Superoxide Dismutase. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201404133] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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27
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Nakane D, Wasada-Tsutsui Y, Funahashi Y, Hatanaka T, Ozawa T, Masuda H. A Novel Square-Planar Ni(II) Complex with an Amino—Carboxamido—Dithiolato-Type Ligand as an Active-Site Model of NiSOD. Inorg Chem 2014; 53:6512-23. [DOI: 10.1021/ic402574d] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Daisuke Nakane
- Department
of Frontier Materials, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan
| | - Yuko Wasada-Tsutsui
- Department
of Frontier Materials, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan
| | - Yasuhiro Funahashi
- Department
of Chemistry, Graduate School of Science, Osaka University, 1-1
Machikaneyama, Toyonaka, Osaka 560-0043, Japan
| | - Tsubasa Hatanaka
- Department
of Chemistry, Graduate School of Science, Osaka University, 1-1
Machikaneyama, Toyonaka, Osaka 560-0043, Japan
| | - Tomohiro Ozawa
- Department
of Frontier Materials, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan
| | - Hideki Masuda
- Department
of Frontier Materials, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan
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28
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Shearer J. Dioxygen and superoxide stability of metallopeptide based mimics of nickel containing superoxide dismutase: The influence of amine/amidate vs. bis-amidate ligation. J Inorg Biochem 2013; 129:145-9. [DOI: 10.1016/j.jinorgbio.2013.09.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2013] [Revised: 08/07/2013] [Accepted: 09/02/2013] [Indexed: 10/26/2022]
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29
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Faiella M, Roy A, Sommer D, Ghirlanda G. De novo design of functional proteins: Toward artificial hydrogenases. Biopolymers 2013; 100:558-71. [DOI: 10.1002/bip.22420] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2013] [Revised: 07/08/2013] [Accepted: 09/18/2013] [Indexed: 12/18/2022]
Affiliation(s)
- Marina Faiella
- Department of Chemistry and Biochemistry; Arizona State University; Tempe AZ
| | - Anindya Roy
- Department of Chemistry and Biochemistry; Arizona State University; Tempe AZ
| | - Dayn Sommer
- Department of Chemistry and Biochemistry; Arizona State University; Tempe AZ
| | - Giovanna Ghirlanda
- Department of Chemistry and Biochemistry; Arizona State University; Tempe AZ
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30
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Dutta A, Flores M, Roy S, Schmitt JC, Hamilton GA, Hartnett HE, Shearer J, Jones AK. Sequential oxidations of thiolates and the cobalt metallocenter in a synthetic metallopeptide: implications for the biosynthesis of nitrile hydratase. Inorg Chem 2013; 52:5236-45. [PMID: 23587023 PMCID: PMC4046696 DOI: 10.1021/ic400171z] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Cobalt nitrile hydratases (Co-NHase) contain a catalytic cobalt(III) ion coordinated in an N2S3 first coordination sphere composed of two amidate nitrogens and three cysteine-derived sulfur donors: a thiolate (-SR), a sulfenate (-S(R)O(-)), and a sulfinate (-S(R)O2(-)). The sequence of biosynthetic reactions that leads to the post-translational oxidations of the metal and the sulfur ligands is unknown, but the process is believed to be initiated directly by oxygen. Herein we utilize cobalt bound in an N2S2 first coordination sphere by a seven amino acid peptide known as SODA (ACDLPCG) to model this oxidation process. Upon exposure to oxygen, Co-SODA is oxidized in two steps. In the first fast step (seconds), magnetic susceptibility measurements demonstrated that the metallocenter remains paramagnetic, that is, Co(2+), and sulfur K-edge X-ray absorption spectroscopy (XAS) is used to show that one of the thiolates is oxidized to sulfinate. In a second process on a longer time scale (hours), magnetic susceptibility measurements and Co K-edge XAS show that the metal is oxidized to Co(3+). Unlike other model complexes, additional slow oxidation of the second thiolate in Co-SODA is not observed, and a catalytically active complex is never formed. The likely reason is the absence of the axial thiolate ligand. In essence, the reactivity of Co-SODA can be described as between previously described models which either quickly convert to final product or are stable in air, and it offers a first glimpse into a possible oxidation pathway for nitrile hydratase biosynthesis.
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Affiliation(s)
- Arnab Dutta
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287
- Center for Bio-Inspired Solar Fuel Production, Arizona State University, Tempe, AZ 85287
| | - Marco Flores
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287
| | - Souvik Roy
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287
- Center for Bio-Inspired Solar Fuel Production, Arizona State University, Tempe, AZ 85287
| | | | | | - Hilairy E. Hartnett
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287
- School of Earth and Space Exploration; Arizona State University, Tempe, AZ 85287
| | - Jason Shearer
- Department of Chemistry, University of Nevada, Reno, Nevada 89557
| | - Anne K. Jones
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287
- Center for Bio-Inspired Solar Fuel Production, Arizona State University, Tempe, AZ 85287
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31
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Shearer J. Use of a metallopeptide-based mimic provides evidence for a proton-coupled electron-transfer mechanism for superoxide reduction by nickel-containing superoxide dismutase. Angew Chem Int Ed Engl 2013; 52:2569-72. [PMID: 23341243 DOI: 10.1002/anie.201209746] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2012] [Indexed: 11/10/2022]
Abstract
Sneaky little SOD! A metallopeptide-based mimic of nickel-containing superoxide dismutase was used to probe the mechanism of superoxide reduction by the metalloenzyme. Kinetic studies suggest a proton-coupled electron-transfer mechanism; large H/D kinetic isotope effects (KIE) are observed. XAS studies suggest the transferred H-atom is in the form of a Ni(II) -S(H)-Cys moiety.
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Affiliation(s)
- Jason Shearer
- Department of Chemistry, University of Nevada, Reno, NV 89557, USA.
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32
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Shearer J. Use of a Metallopeptide-Based Mimic Provides Evidence for a Proton-Coupled Electron-Transfer Mechanism for Superoxide Reduction by Nickel-Containing Superoxide Dismutase. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201209746] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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33
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Liu Y, Wang Q, Wei Y, Lin YW, Li W, Su JH, Wang Z, Tian Y, Huang ZX, Tan X. Functional conversion of nickel-containing metalloproteins via molecular design: from a truncated acetyl-coenzyme A synthase to a nickel superoxide dismutase. Chem Commun (Camb) 2013; 49:1452-4. [DOI: 10.1039/c2cc38224e] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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34
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Macholl S, Tietze D, Buntkowsky G. NMR crystallography of amides, peptides and protein–ligand complexes. CrystEngComm 2013. [DOI: 10.1039/c3ce40908b] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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35
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Broering EP, Truong PT, Gale EM, Harrop TC. Synthetic Analogues of Nickel Superoxide Dismutase: A New Role for Nickel in Biology. Biochemistry 2012; 52:4-18. [DOI: 10.1021/bi3014533] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Ellen P. Broering
- Department
of Chemistry and Center for Metalloenzyme
Studies, The University of Georgia, 1001
Cedar Street, Athens, Georgia 30602, United States
| | - Phan T. Truong
- Department
of Chemistry and Center for Metalloenzyme
Studies, The University of Georgia, 1001
Cedar Street, Athens, Georgia 30602, United States
| | - Eric M. Gale
- Department
of Chemistry and Center for Metalloenzyme
Studies, The University of Georgia, 1001
Cedar Street, Athens, Georgia 30602, United States
| | - Todd C. Harrop
- Department
of Chemistry and Center for Metalloenzyme
Studies, The University of Georgia, 1001
Cedar Street, Athens, Georgia 30602, United States
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36
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Krause ME, Glass AM, Jackson TA, Laurence JS. Embedding the Ni-SOD mimetic Ni-NCC within a polypeptide sequence alters the specificity of the reaction pathway. Inorg Chem 2012; 52:77-83. [PMID: 23214928 DOI: 10.1021/ic301175f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The unique metal abstracting peptide asparagine-cysteine-cysteine (NCC) binds nickel in a square planar 2N:2S geometry and acts as a mimic of the enzyme nickel superoxide dismutase (Ni-SOD). The Ni-NCC tripeptide complex undergoes rapid, site-specific chiral inversion to dld-NCC in the presence of oxygen. Superoxide scavenging activity increases proportionally with the degree of chiral inversion. Characterization of the NCC sequence within longer peptides with absorption, circular dichroism (CD), and magnetic CD (MCD) spectroscopies and mass spectrometry (MS) shows that the geometry of metal coordination is maintained, though the electronic properties of the complex are varied to a small extent because of bis-amide, rather than amine/amide, coordination. In addition, both Ni-tripeptide and Ni-pentapeptide complexes have charges of -2. This study demonstrates that the chiral inversion chemistry does not occur when NCC is embedded in a longer polypeptide sequence. Nonetheless, the superoxide scavenging reactivity of the embedded Ni-NCC module is similar to that of the chirally inverted tripeptide complex, which is consistent with a minor change in the reduction potential for the Ni-pentapeptide complex. Together, this suggests that the charge of the complex could affect the SOD activity as much as a change in the primary coordination sphere. In Ni-NCC and other Ni-SOD mimics, changes in chirality, superoxide scavenging activity, and oxidation of the peptide itself all depend on the presence of dioxygen or its reduced derivatives (e.g., superoxide), and the extent to which each of these distinct reactions occurs is ruled by electronic and steric effects that emenate from the organization of ligands around the metal center.
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Affiliation(s)
- Mary E Krause
- Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, Kansas 66047, United States
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37
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Dutta A, Hamilton GA, Hartnett HE, Jones AK. Construction of heterometallic clusters in a small peptide scaffold as [NiFe]-hydrogenase models: development of a synthetic methodology. Inorg Chem 2012; 51:9580-8. [PMID: 22924594 DOI: 10.1021/ic2026818] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
[NiFe]-hydrogenases are enzymes that catalyze the reversible interconversion of protons and hydrogen at a heterobimetallic site containing Ni and Fe. This organometallic site has served as an inspiration for the synthesis of a number of biomimetic complexes, but, unfortunately, most close structural mimics have shown little to no reactivity with either of the substrates for hydrogenases. This suggests that interactions between the metallo-active site and the protein scaffold are crucial in tuning reactivity. As a first step toward development of peptide-based models, in this paper we demonstrate a synthetic strategy for construction of peptide coordinated, cysteinyl thiolate bridged Ni-M complexes in which M is a hetero-organometallic fragment. We utilize the seven amino acid peptide ACDLPCG as a scaffold for construction of these peptide-coordinated metallocenters. This peptide binds Ni in an N(2)S(2) environment consisting of the amino terminus, an amide nitrogen, and the two cysteinyl thiolates. We show that these thiolates serve as reactive sites for formation of heterometallic complexes in which they serve as bridging ligands. The method is general, and a number of heterometallic fragments including Ru(η(6)-arene)(2+), M(CO)(4)(piperidine) for M = Mo and W, and Fe(2)(CO)(6) were successfully incorporated, and the resulting metallopeptides characterized via a range of spectroscopic techniques. This methodology serves as the first step to construction of hydrogenase peptidomimetics that incorporate defined outer coordination sphere interactions intended to tune reactivity.
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Affiliation(s)
- Arnab Dutta
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287, USA
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38
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Herdt DR, Grapperhaus CA. Kinetic study of nickel-thiolate oxygenation by hydrogen peroxide. Implications for nickel-containing superoxide dismutase. Dalton Trans 2012; 41:364-6. [DOI: 10.1039/c1dt11300c] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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39
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Lee WZ, Chiang CW, Lin TH, Kuo TS. A Discrete Five-Coordinate NiIII Complex Resembling the Active Site of the Oxidized Form of Nickel Superoxide Dismutase. Chemistry 2011; 18:50-3. [DOI: 10.1002/chem.201102690] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2011] [Revised: 10/20/2011] [Indexed: 11/08/2022]
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40
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Gale EM, Cowart DM, Scott RA, Harrop TC. Dipeptide-based models of nickel superoxide dismutase: solvent effects highlight a critical role to Ni-S bonding and active site stabilization. Inorg Chem 2011; 50:10460-71. [PMID: 21932766 PMCID: PMC3561719 DOI: 10.1021/ic2016462] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Nickel superoxide dismutase (Ni-SOD) catalyzes the disproportionation of the superoxide radical to O(2) and H(2)O(2) utilizing the Ni(III/II) redox couple. The Ni center in Ni-SOD resides in an unusual coordination environment that is distinct from other SODs. In the reduced state (Ni-SOD(red)), Ni(II) is ligated to a primary amine-N from His1, anionic carboxamido-N/thiolato-S from Cys2, and a second thiolato-S from Cys6 to complete a NiN(2)S(2) square-planar coordination motif. Utilizing the dipeptide N(2)S(2-) ligand, H(2)N-Gly-l-Cys-OMe (GC-OMeH(2)), an accurate model of the structural and electronic contributions provided by His1 and Cys2 in Ni-SOD(red), we constructed the dinuclear sulfur-bridged metallosynthon, [Ni(2)(GC-OMe)(2)] (1). From 1 we prepared the following monomeric Ni(II)-N(2)S(2) complexes: K[Ni(GC-OMe)(SC(6)H(4)-p-Cl)] (2), K[Ni(GC-OMe)(S(t)Bu)] (3), K[Ni(GC-OMe)(SC(6)H(4)-p-OMe)] (4), and K[Ni(GC-OMe)(SNAc)] (5). The design strategy in utilizing GC-OMe(2-) is analogous to one which we reported before (see Inorg. Chem. 2009, 48, 5620 and Inorg. Chem. 2010, 49, 7080) where Ni-SOD(red) active site mimics can be assembled at will with electronically variant RS(-) ligands. Discussed herein is our initial account pertaining to the aqueous behavior of isolable, small-molecule Ni-SOD model complexes (non-maquette based). Spectroscopic (FTIR, UV-vis, ESI-MS, XAS) and electrochemical (CV) measurements suggest that 2-5 successfully simulate many of the electronic features of Ni-SOD(red). Furthermore, the aqueous studies reveal a dynamic behavior with regard to RS(-) lability and bridging interactions, suggesting a stabilizing role brought about by the protein architecture.
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Affiliation(s)
- Eric M. Gale
- Department of Chemistry, University of Georgia, 1001 Cedar Street, Athens, Georgia 30602
| | - Darin M. Cowart
- Department of Chemistry, University of Georgia, 1001 Cedar Street, Athens, Georgia 30602
| | - Robert A. Scott
- Department of Chemistry, University of Georgia, 1001 Cedar Street, Athens, Georgia 30602
| | - Todd C. Harrop
- Department of Chemistry, University of Georgia, 1001 Cedar Street, Athens, Georgia 30602
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41
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Gale EM, Simmonett AC, Telser J, Schaefer HF, Harrop TC. Toward Functional Ni-SOD Biomimetics: Achieving a Structural/Electronic Correlation with Redox Dynamics. Inorg Chem 2011; 50:9216-8. [DOI: 10.1021/ic201822f] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Eric M. Gale
- Department of Chemistry and Center for Computational Chemistry, The University of Georgia, 1001 Cedar Street, Athens, Georgia 30602, United States
| | - Andrew C. Simmonett
- Department of Chemistry and Center for Computational Chemistry, The University of Georgia, 1001 Cedar Street, Athens, Georgia 30602, United States
| | - Joshua Telser
- Department of Biological, Chemical and Physical Sciences, Roosevelt University, 430 South Michigan Avenue, Chicago, Illinois 60605, United States
| | - Henry F. Schaefer
- Department of Chemistry and Center for Computational Chemistry, The University of Georgia, 1001 Cedar Street, Athens, Georgia 30602, United States
| | - Todd C. Harrop
- Department of Chemistry and Center for Computational Chemistry, The University of Georgia, 1001 Cedar Street, Athens, Georgia 30602, United States
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42
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Zimmerman JR, Smucker BW, Dain RP, Vanstipdonk MJ, Eichhorn DM. Tridentate N(2)S ligand from 2,2'-dithiodibenzaldehyde and N,N-dimethylethylenediamine: Synthesis, structure, and characterization of a Ni(II) complex with relevance to Ni Superoxide Dismutase. Inorganica Chim Acta 2011; 373:54-61. [PMID: 21666847 PMCID: PMC3110705 DOI: 10.1016/j.ica.2011.03.052] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Nickel Superoxide Dismutase (NiSOD) and the A-cluster of Carbon Monoxide Dehydrogenase/Acetyl Coenzyme A Synthase (CODH/ACS) both feature active sites with Ni coordinated by thiolate and amide donors. It is likely that the particular set of donors is important in tuning the redox potential of the Ni center(s). We report herein an expansion of our efforts involving the use of 2,2'-dithiodibenzaldehyde (DTDB) as a synthon for metal-thiolate complexes to reactions with Ni complexes of N,N-dimethylethylenediamine (dmen). In the presence of coordinating counterions, these reactions result in monomeric square-planar complexes of the tridentate N(2)S donor ligand derived from the Schiff-base condensation of dmen and DTDB. In the absence of a coordinating counterion, we have isolated a Ni(II) complex with an asymmetric N(2)S(2) donor set involving one amine and one imine N donor in addition to two thiolate donors. This latter complex is discussed with respect to its relevance to the active site of NiSOD.
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Affiliation(s)
- Joshua R Zimmerman
- Department of Chemistry, Wichita State University, Wichita, KS 67260-0051
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43
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Ma H, Petersen JL, Young VG, Yee GT, Jensen MP. Solid-State Spin Crossover of Ni(II) in a Bioinspired N3S2Ligand Field. J Am Chem Soc 2011; 133:5644-7. [DOI: 10.1021/ja110890v] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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44
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Tietze D, Voigt S, Mollenhauer D, Tischler M, Imhof D, Gutmann T, González L, Ohlenschläger O, Breitzke H, Görlach M, Buntkowsky G. Revealing the Position of the Substrate in Nickel Superoxide Dismutase: A Model Study. Angew Chem Int Ed Engl 2011; 50:2946-50. [DOI: 10.1002/anie.201005027] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2010] [Revised: 11/16/2010] [Indexed: 01/26/2023]
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45
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Tietze D, Voigt S, Mollenhauer D, Tischler M, Imhof D, Gutmann T, González L, Ohlenschläger O, Breitzke H, Görlach M, Buntkowsky G. Bestimmung der Substratposition in der Nickel-Superoxiddismutase: eine Modellstudie. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201005027] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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46
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Nam E, Alokolaro PE, Swartz RD, Gleaves MC, Pikul J, Kovacs JA. Investigation of the mechanism of formation of a thiolate-ligated Fe(III)-OOH. Inorg Chem 2011; 50:1592-602. [PMID: 21284379 DOI: 10.1021/ic101776m] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Kinetic studies aimed at determining the most probable mechanism for the proton-dependent [Fe(II)(S(Me2)N(4)(tren))](+) (1) promoted reduction of superoxide via a thiolate-ligated hydroperoxo intermediate [Fe(III)(S(Me2)N(4)(tren))(OOH)](+) (2) are described. Rate laws are derived for three proposed mechanisms, and it is shown that they should conceivably be distinguishable by kinetics. For weak proton donors with pK(a(HA)) > pK(a(HO(2))) rates are shown to correlate with proton donor pK(a), and display first-order dependence on iron, and half-order dependence on superoxide and proton donor HA. Proton donors acidic enough to convert O(2)(-) to HO(2) (in tetrahydrofuran, THF), that is, those with pK(a(HA)) < pK(a(HO(2))), are shown to display first-order dependence on both superoxide and iron, and rates which are independent of proton donor concentration. Relative pK(a) values were determined in THF by measuring equilibrium ion pair acidity constants using established methods. Rates of hydroperoxo 2 formation displays no apparent deuterium isotope effect, and bases, such as methoxide, are shown to inhibit the formation of 2. Rate constants for p-substituted phenols are shown to correlate linearly with the Hammett substituent constants σ(-). Activation parameters ((ΔH(++) = 2.8 kcal/mol, ΔS(++) = -31 eu) are shown to be consistent with a low-barrier associative mechanism that does not involve extensive bond cleavage. Together, these data are shown to be most consistent with a mechanism involving the addition of HO(2) to 1 with concomitant oxidation of the metal ion, and reduction of superoxide (an "oxidative addition" of sorts), in the rate-determining step. Activation parameters for MeOH- (ΔH(++) = 13.2 kcal/mol and ΔS(++) = -24.3 eu), and acetic acid- (ΔH(++) = 8.3 kcal/mol and ΔS(++) = -34 eu) promoted release of H(2)O(2) to afford solvent-bound [Fe(III)(S(Me2)N(4)(tren))(OMe)](+) (3) and [Fe(III)(S(Me2)N(4)(tren))(O(H)Me)](+) (4), respectively, are shown to be more consistent with a reaction involving rate-limiting protonation of an Fe(III)-OOH, than with one involving rate-limiting O-O bond cleavage. The observed deuterium isotope effect (k(H)/k(D) = 3.1) is also consistent with this mechanism.
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Affiliation(s)
- Elaine Nam
- Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700, USA
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47
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Shearer J, Callan PE, Amie J. Use of metallopeptide based mimics demonstrates that the metalloprotein nitrile hydratase requires two oxidized cysteinates for catalytic activity. Inorg Chem 2010; 49:9064-77. [PMID: 20831172 PMCID: PMC3570060 DOI: 10.1021/ic101765h] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Nitrile hydratases (NHases) are non-heme Fe(III) or non-corrin Co(III) containing metalloenzymes that possess an N(2)S(3) ligand environment with nitrogen donors derived from amidates and sulfur donors derived from cysteinates. A closely related enzyme is thiocyanate hydrolase (SCNase), which possesses a nearly identical active-site coordination environment as CoNHase. These enzymes are redox inactive and perform hydrolytic reactions; SCNase hydrolyzes thiocyanate anions while NHase converts nitriles into amides. Herein an active CoNHase metallopeptide mimic, [Co(III)NHase-m1] (NHase-m1 = AcNH-CCDLP-CGVYD-PA-COOH), that contains Co(III) in a similar N(2)S(3) coordination environment as CoNHase is reported. [Co(III)NHase-m1] was characterized by electrospray ionization-mass spectrometry (ESI-MS), gel-permeation chromatography (GPC), Co K-edge X-ray absorption spectroscopy (Co-S: 2.21 Å; Co-N: 1.93 Å), vibrational, and optical spectroscopies. We find that [Co(III)NHase-m1] will perform the catalytic conversion of acrylonitrile into acrylamide with up to 58 turnovers observed after 18 h at 25 °C (pH 8.0). FTIR data used in concert with calculated vibrational data (mPWPW91/aug-cc-TZVPP) demonstrates that the active form of [Co(III)NHase-m1] has a ligated SO(2) (ν = 1091 cm(-1)) moiety and a ligated protonated SO(H) (ν = 928 cm(-1)) moiety; when only one oxygenated cysteinate ligand (i.e., a mono-SO(2) coordination motif) or the bis-SO(2) coordination motif are found within [Co(III)NHase-m1] no catalytic activity is observed. Calculations of the thermodynamics of ligand exchange (B3LYP/aug-cc-TZVPP) suggest that the reason for this is that the SO(2)/SO(H) equatorial ligand motif promotes both water dissociation from the Co(III)-center and nitrile coordination to the Co(III)-center. In contrast, the under- or overoxidized motifs will either strongly favor a five coordinate Co(III)-center or strongly favor water binding to the Co(III)-center over nitrile binding.
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Affiliation(s)
- Jason Shearer
- Department of Chemistry, University of Nevada, Reno, Nevada 89557, USA.
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48
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Gale EM, Patra AK, Harrop TC. Versatile methodology toward NiN(2)S(2) complexes as nickel superoxide dismutase models: structure and proton affinity. Inorg Chem 2010; 48:5620-2. [PMID: 20507097 DOI: 10.1021/ic9009042] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Structural features of the reduced form of the nickel superoxide dismutase (Ni-SOD) active site have been modeled with asymmetric NiN(2)S(2) complexes (Et(4)N)[Ni(nmp)(SR)] (R = C(6)H(4)-p-Cl (2) and (S(t)Bu) (3)) obtained via S,S-bridge splitting of the dimeric metallosynthon, [Ni(2)(nmp)(2)] (1). Complexes 2 and 3 are irreversibly oxidized at potentials within the window needed for SOD activity, 236 and 75 mV versus Ag/AgCl, respectively. The exogenous thiolato-S in 2 and 3 serves as a proton acceptor, suggesting potential involvement of Cys6 in Ni-SOD for H(+) storage between SOD half reactions.
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Affiliation(s)
- Eric M Gale
- Department of Chemistry, University of Georgia, 1001 Cedar St, Athens, Georgia 30602, USA
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Tietze D, Tischler M, Voigt S, Imhof D, Ohlenschläger O, Görlach M, Buntkowsky G. Development of a functional cis-prolyl bond biomimetic and mechanistic implications for nickel superoxide dismutase. Chemistry 2010; 16:7572-8. [PMID: 20461826 DOI: 10.1002/chem.200903306] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
During recent years several peptide-based Ni superoxide dismutase (NiSOD) models have been developed. These NiSOD models show an important structural difference compared to the native NiSOD enzyme, which could cause a completely different mechanism of superoxide dismutation. In the native enzyme the peptide bond between Leu4 and Pro5 is cis-configured, while the NiSOD models exhibit a trans-configured peptide bond between these two residues. To shed light on how the configuration of this single peptide bond influences the activity of the NiSOD model peptides, a new cis-prolyl bond surrogate was developed. As surrogate we chose a leucine/alanine-based disubstituted 1,2,3-triazole, which was incorporated into the NiSOD model peptide replacing residues Leu4 and Pro5. The yielded 1,5-disubstituted triazole nickel peptide exhibited high SOD activity, which was approximately the same activity as its parent trans-configured analogue. Hence, the conformation of the prolyl peptide bond apparently has of minor importance for the catalytic activity of the metallopeptides as postulated in literature. Furthermore, it is shown that the triazole metallopeptide is forming a stable cyanide adduct as a substrate analogue model complex.
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Affiliation(s)
- Daniel Tietze
- Technische Universität Darmstadt, Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Petersenstr. 22, 64287 Darmstadt, Germany
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50
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Gale EM, Narendrapurapu BS, Simmonett AC, Schaefer HF, Harrop TC. Exploring the Effects of H-Bonding in Synthetic Analogues of Nickel Superoxide Dismutase (Ni-SOD): Experimental and Theoretical Implications for Protection of the Ni−SCys Bond. Inorg Chem 2010; 49:7080-96. [DOI: 10.1021/ic1009187] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Eric M. Gale
- Department of Chemistry and Center for Computational Chemistry, University of Georgia, 1001 Cedar Street, Athens, Georgia 30602
| | - Beulah S. Narendrapurapu
- Department of Chemistry and Center for Computational Chemistry, University of Georgia, 1001 Cedar Street, Athens, Georgia 30602
| | - Andrew C. Simmonett
- Department of Chemistry and Center for Computational Chemistry, University of Georgia, 1001 Cedar Street, Athens, Georgia 30602
| | - Henry F. Schaefer
- Department of Chemistry and Center for Computational Chemistry, University of Georgia, 1001 Cedar Street, Athens, Georgia 30602
| | - Todd C. Harrop
- Department of Chemistry and Center for Computational Chemistry, University of Georgia, 1001 Cedar Street, Athens, Georgia 30602
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