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Bhattacharyya M, Hossain M. Picomolar level sensorial dual colorimetric gold nanoparticle sensor for Zn 2+ and Hg 2+ ions synthesized from bark extract of Lannea Grandis Coromandelica and its wide range applications in real sample analysis. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2024; 308:123682. [PMID: 38042120 DOI: 10.1016/j.saa.2023.123682] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Revised: 11/07/2023] [Accepted: 11/21/2023] [Indexed: 12/04/2023]
Abstract
In this work a facile, rapid, reproducible and non-toxic approach has been demonstrated for synthesis of most stable AuNPs from bark extract of Lannea Grandis Coromandelica. UV-Visible spectroscopy, FTIR, TEM, SAED, EDX, XRD, DLS, Zeta Potential, FE-SEM, AFM and XPS techniques were employed for the characterization of synthesized LGC-AuNPs. The UV-Vis spectra of LGC-AuNPs gave SPR peak at 536 nm while the TEM analysis revealed LGC-AuNPs have 20.75 nm size with spherical in shape. DLS study showed the AuNPs have average diameter 50.18 nm. The synthesized AuNPs exhibited very high selectivity, rapid response in recognition towards Zn2+ and Hg2+ ions by changing its color within 20 sec. This proposed sensor can detect very low picomolar level of Zn2+ and Hg2+ ions (LOD value for Zn2+ and Hg2+ were found 1.36 pM and 24.60 pM respectively). Here we also studied effect of several factors such as variation of conc of gold, temperature, incubation time, pH, salt, solvent (polar protic and polar aprotic) to know in which condition AuNPs have high stability and sensitivity. The data revealed that synthesized AuNPs was stable up to two years at pH 6.5 at room temperature in water media and under this condition, it shows maximum sensitivity and reactivity. Moreover, here interference study was carried out to identify high selectivity of synthesized LGC-AuNPs probe in presence of different metal ions. The real sample analyses also revealed the great applicability of this probe. Therefore, this simple, rapid, low-cost, sensing activity appeared to hold great sensibleness for detection of heavy metal ions in real sample.
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Kavitha V, Chitra K, Gomathi A, Dhivya R, Viswanathamurthi P. Sensing of Pyrophosphate Anion by a Fluorescent Zn(II) Complex Bearing Acenaphthene Imidazole Moiety. JOURNAL OF ANALYTICAL CHEMISTRY 2022. [DOI: 10.1134/s1061934822070115] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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3
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Cysteine driven decomposition and quenching of a fluorescent metalloreceptor: Optical detection and mechanistic insight. Inorganica Chim Acta 2022. [DOI: 10.1016/j.ica.2021.120739] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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4
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Ivanova B, Spiteller M. Crystallographic and theoretical study of the atypical distorted octahedral geometry of the metal chromophore of zinc(II) bis((1R,2R)-1,2-diaminocyclohexane) dinitrate. J Mol Struct 2022. [DOI: 10.1016/j.molstruc.2021.131488] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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5
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Roberts CS, Ni F, Mitra B. The Zinc and Iron Binuclear Transport Center of ZupT, a ZIP Transporter from Escherichia coli. Biochemistry 2021; 60:3738-3752. [PMID: 34793140 DOI: 10.1021/acs.biochem.1c00621] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
ZupT fromEscherichia coliis a member of the Zrt-/Irt-like Protein (ZIP) transporter family, which is responsible for zinc uptake during zinc-sufficient conditions. ZIP transporters have been shown to transport different divalent metal ions including zinc, iron, manganese, and cadmium. In this study, we show that ZupT has an asymmetric binuclear metal center in the transmembrane domain; one metal-binding site, M1, binds zinc, cadmium, and iron, while the other, M2, binds iron only and with higher affinity than M1. Using site-specific mutagenesis and transport activity measurements in whole cells and proteoliposomes, we show that zinc is transported from M1, while iron is transported from M2. The two sites share a common bridging ligand, a conserved glutamate residue. M1 and M2 have ligands from highly conserved motifs in transmembrane domains 4 and 5. Additionally, M2 has a ligand from transmembrane domain 6, a glutamate residue, which is conserved in the gufA subfamily of ZIP transporters, including ZupT and the human ZIP11. Unlike cadmium, iron transport from M2 does not inhibit the zinc transport activity but slightly stimulates it. This stimulation of activity is mediated through the bridging carboxylate ligand. The binuclear zinc-iron binding center in ZupT has likely evolved to enable the transport of essential metals from two different sites without competition; a similar mechanism of metal transport is likely to be found in the gufA subfamily of ZIP transporter proteins.
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Affiliation(s)
- Cameron S Roberts
- Department of Biochemistry, Microbiology and Immunology, School of Medicine, Wayne State University, Detroit, Michigan 48201, United States
| | - Fei Ni
- Department of Biochemistry, Microbiology and Immunology, School of Medicine, Wayne State University, Detroit, Michigan 48201, United States
| | - Bharati Mitra
- Department of Biochemistry, Microbiology and Immunology, School of Medicine, Wayne State University, Detroit, Michigan 48201, United States
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6
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Principles and practice of determining metal-protein affinities. Biochem J 2021; 478:1085-1116. [PMID: 33710331 PMCID: PMC7959690 DOI: 10.1042/bcj20200838] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Revised: 02/05/2021] [Accepted: 02/11/2021] [Indexed: 01/02/2023]
Abstract
Metal ions play many critical roles in biology, as structural and catalytic cofactors, and as cell regulatory and signalling elements. The metal–protein affinity, expressed conveniently by the metal dissociation constant, KD, describes the thermodynamic strength of a metal–protein interaction and is a key parameter that can be used, for example, to understand how proteins may acquire metals in a cell and to identify dynamic elements (e.g. cofactor binding, changing metal availabilities) which regulate protein metalation in vivo. Here, we outline the fundamental principles and practical considerations that are key to the reliable quantification of metal–protein affinities. We review a selection of spectroscopic probes which can be used to determine protein affinities for essential biological transition metals (including Mn(II), Fe(II), Co(II), Ni(II), Cu(I), Cu(II) and Zn(II)) and, using selected examples, demonstrate how rational probe selection combined with prudent experimental design can be applied to determine accurate KD values.
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7
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Kulesha A, Yoon JH, Chester C, D'Souza A, Costeas C, Makhlynets OV. Contributions of primary coordination ligands and importance of outer sphere interactions in UFsc, a de novo designed protein with high affinity for metal ions. J Inorg Biochem 2020; 212:111224. [PMID: 32871348 DOI: 10.1016/j.jinorgbio.2020.111224] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Revised: 08/04/2020] [Accepted: 08/05/2020] [Indexed: 12/15/2022]
Abstract
Metalloproteins constitute nearly half of all proteins and catalyze some of the most complex chemical reactions. Recently, we reported a design of 4G-UFsc (Uno Ferro single chain), a single chain four-helical bundle with extraordinarily high (30 pM) affinity for zinc. We evaluated the contribution of different side chains to binding of Co(II), Ni(II), Zn(II) and Mn(II) using systematic mutagenesis of the amino acids that constitute the primary metal coordination and outer spheres. The binding affinity of proteins for metals was then measured using isothermal titration calorimetry. Our results show that both primary metal coordination environment and side chains in the outer sphere of UFsc are highly sensitive to even slight changes and can be adapted to binding different 3d metals, including hard-to-tightly bind metal ions such as Mn(II). The studies on the origins of tight metal binding will guide future metalloprotein design efforts.
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Affiliation(s)
- Alona Kulesha
- Department of Chemistry, Syracuse University, 111 College Place, Syracuse, NY 13244, United States
| | - Jennifer H Yoon
- Department of Chemistry, Syracuse University, 111 College Place, Syracuse, NY 13244, United States
| | - Cara Chester
- Department of Chemistry, Syracuse University, 111 College Place, Syracuse, NY 13244, United States
| | - Areetha D'Souza
- Department of Chemistry, Syracuse University, 111 College Place, Syracuse, NY 13244, United States
| | - Christos Costeas
- Department of Chemistry, Syracuse University, 111 College Place, Syracuse, NY 13244, United States
| | - Olga V Makhlynets
- Department of Chemistry, Syracuse University, 111 College Place, Syracuse, NY 13244, United States.
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8
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Padjasek M, Kocyła A, Kluska K, Kerber O, Tran JB, Krężel A. Structural zinc binding sites shaped for greater works: Structure-function relations in classical zinc finger, hook and clasp domains. J Inorg Biochem 2020; 204:110955. [DOI: 10.1016/j.jinorgbio.2019.110955] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Revised: 11/08/2019] [Accepted: 12/01/2019] [Indexed: 12/12/2022]
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9
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Koebke KJ, Batelu S, Kandegedara A, Smith SR, Stemmler TL. Refinement of protein Fe(II) binding characteristics utilizing a competition assay exploiting small molecule ferrous chelators. J Inorg Biochem 2020; 203:110882. [PMID: 31683123 DOI: 10.1016/j.jinorgbio.2019.110882] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2019] [Revised: 10/03/2019] [Accepted: 10/04/2019] [Indexed: 12/20/2022]
Abstract
Iron is the most prevalent metal in biology. Its chemical and redox versatility allows it to direct activity of many Fe binding proteins. While iron's biological applications are diverse, challenges inherent in having Fe(II) present at high abundance means cells must ensure delivery to the correct recipient, while also ensuring its chemistry is regulated. Having a detailed understanding of the biophysical characteristics of a protein's iron binding characteristics allows us to understand general cellular metal homeostasis events. Unfortunately, most spectroscopic techniques available to measure metal binding affinity require protein be in a homogeneous state. Homogeneity creates an artificial environment when measuring metal binding since within cells numerous additional metal binding biomolecules compete with the target. Here we investigate commercially available Fe(II) chelators with spectral markers coupled to metal binding and release. Our goal was to determine their utility as competitors while measuring aspects of metal binding by apoproteins during a metal binding competition assay. Adding chelators during apoprotein metal binding mimics heterogeneous metal binding environments present in vivo, and provides a more realistic metal binding affinity measurement. Ferrous chelators explored within this report include: Rhod-5N, Magfura-2, Fura-4F, Fura-2, and TPA (Tris-(2-byridyl-methyl)amine; each forms a 1:1 complex with Fe(II) and combined cover a binding range of 5 orders of magnitude (micromolar to nanomolar Kd). These chelators were used to calibrate binding affinities for yeast and fly frataxin (Yfh1 and Dfh, respectively), involved in mitochondrial FeS cluster bioassembly.
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Affiliation(s)
- Karl J Koebke
- Department of Pharmaceutical Sciences, Wayne State University, Detroit, MI 48201, USA
| | - Sharon Batelu
- Department of Pharmaceutical Sciences, Wayne State University, Detroit, MI 48201, USA
| | - Ashoka Kandegedara
- Department of Pharmaceutical Sciences, Wayne State University, Detroit, MI 48201, USA
| | - Sheila R Smith
- Department of Natural Sciences, University of Michigan-Dearborn, Dearborn, MI 48101, USA
| | - Timothy L Stemmler
- Department of Pharmaceutical Sciences, Wayne State University, Detroit, MI 48201, USA.
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10
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Liu CH, Dugas LD, Bowman JI, Chidanguro T, Storey RF, Simon YC. Forcing single-chain nanoparticle collapse through hydrophobic solvent interactions in comb copolymers. Polym Chem 2020. [DOI: 10.1039/c9py01235d] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We demonstrate that we can tune the chain collapse of comb copolymers into single-chain nanoparticles upon UV irradiation through solvency control.
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Affiliation(s)
- Cheyenne H. Liu
- School of Polymer Science and Engineering
- The University of Southern Mississippi
- Hattiesburg
- USA
| | - Logan D. Dugas
- School of Polymer Science and Engineering
- The University of Southern Mississippi
- Hattiesburg
- USA
| | - Jared I. Bowman
- School of Polymer Science and Engineering
- The University of Southern Mississippi
- Hattiesburg
- USA
| | - Tamuka Chidanguro
- School of Polymer Science and Engineering
- The University of Southern Mississippi
- Hattiesburg
- USA
| | - Robson F. Storey
- School of Polymer Science and Engineering
- The University of Southern Mississippi
- Hattiesburg
- USA
| | - Yoan C. Simon
- School of Polymer Science and Engineering
- The University of Southern Mississippi
- Hattiesburg
- USA
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11
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Sorenson AE, Schaeffer PM. A new bivalent fluorescent fusion protein for differential Cu(II) and Zn(II) ion detection in aqueous solution. Anal Chim Acta 2019; 1101:120-128. [PMID: 32029102 DOI: 10.1016/j.aca.2019.12.017] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 12/06/2019] [Accepted: 12/08/2019] [Indexed: 12/15/2022]
Abstract
Simple and easy to engineer metal-sensing molecules that are capable of differentiating metal ions and producing metal-specific signals are highly desirable. Metal ions affect the thermal stability of proteins by increasing or decreasing their resistance to unfolding. This work illustrates a new strategy for designing bivalent fluorescent fusion proteins capable of differentiating metal ions in solution through their distinct effects on a protein's thermal stability. A new dual purpose metal sensor was developed consisting of biotin protein ligase (BirA) from B. pseudomallei (Bp) fused to green fluorescent protein (GFP). When coupled with differential scanning fluorimetry of GFP-tagged proteins (DSF-GTP) for signal-transduction detection, Bp BirA-GFP yields distinct protein unfolding signatures with Zn(II) and Cu(II) ions in aqueous solutions. The limit of detection of the system is ∼1 μM for both metal species. The system can be used in a variety of high-throughput assay formats including for the screening of metal-binding proteins and chelators. Bp BirA-GFP has also the additional benefit of being useful in Cu(II) ion field-testing applications through simple visual observation of a temperature-dependent loss of fluorescence. Bp BirA-GFP is the first example of a 2protein-based dual purpose Cu(II) and Zn(II) ion sensor compatible with two different yet complementary signal-transduction detection systems.
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Affiliation(s)
- A E Sorenson
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD, 4811, Australia
| | - P M Schaeffer
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD, 4811, Australia.
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12
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Zamora-Carreras H, Maestro B, Sanz JM, Jiménez MA. Turncoat Polypeptides: We Adapt to Our Environment. Chembiochem 2019; 21:432-441. [PMID: 31456307 DOI: 10.1002/cbic.201900446] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Indexed: 01/25/2023]
Abstract
A common interpretation of Anfinsen's hypothesis states that one amino acid sequence should fold into a single, native, ordered state, or a highly similar set thereof, coinciding with the global minimum in the folding-energy landscape, which, in turn, is responsible for the function of the protein. However, this classical view is challenged by many proteins and peptide sequences, which can adopt exchangeable, significantly dissimilar conformations that even fulfill different biological roles. The similarities and differences of concepts related to these proteins, mainly chameleon sequences, metamorphic proteins, and switch peptides, which are all denoted herein "turncoat" polypeptides, are reviewed. As well as adding a twist to the conventional view of protein folding, the lack of structural definition adds clear versatility to the activity of proteins and can be used as a tool for protein design and further application in biotechnology and biomedicine.
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Affiliation(s)
- Héctor Zamora-Carreras
- Instituto de Química-Física Rocasolano (IQFR), Consejo Superior de Investigaciones Científicas (CSIC), Serrano 119, 28006, Madrid, Spain
| | - Beatriz Maestro
- Centro de Investigaciones Biológicas (CIB), Consejo Superior de Investigaciones Científicas (CSIC), Ramiro de Maeztu 9, 28040, Madrid, Spain
| | - Jesús M Sanz
- Centro de Investigaciones Biológicas (CIB), Consejo Superior de Investigaciones Científicas (CSIC), Ramiro de Maeztu 9, 28040, Madrid, Spain.,Centro de Investigación Biomédica en Red de Enfermedades Respiratorias (CIBERES), Av. Monforte de Lemos, 3-5. Pabellón, 28029, Madrid, Spain
| | - M Angeles Jiménez
- Instituto de Química-Física Rocasolano (IQFR), Consejo Superior de Investigaciones Científicas (CSIC), Serrano 119, 28006, Madrid, Spain
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13
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A PCBP1-BolA2 chaperone complex delivers iron for cytosolic [2Fe-2S] cluster assembly. Nat Chem Biol 2019; 15:872-881. [PMID: 31406370 PMCID: PMC6702080 DOI: 10.1038/s41589-019-0330-6] [Citation(s) in RCA: 78] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Accepted: 06/26/2019] [Indexed: 12/13/2022]
Abstract
Hundreds of cellular proteins require iron cofactors for activity, and cells express systems for their assembly and distribution. Molecular details of the cytosolic iron pool used for iron cofactors are lacking, but iron chaperones of the poly(rC)-binding protein (PCBP) family play a key role in ferrous ion distribution. Here we show that, in cells and in vitro, PCBP1 coordinates iron via conserved cysteine and glutamate residues and a molecule of noncovalently bound glutathione (GSH). Proteomics analysis of PCBP1-interacting proteins identified BolA2, which functions, in complex with Glrx3, as a cytosolic [2Fe-2S] cluster chaperone. The Fe-GSH-bound form of PCBP1 complexes with cytosolic BolA2 via a bridging Fe ligand. Biochemical analysis of PCBP1 and BolA2, in cells and in vitro, indicates that PCBP1-Fe-GSH-BolA2 serves as an intermediate complex required for the assembly of [2Fe-2S] clusters on BolA2-Glrx3, thereby linking the ferrous iron and Fe-S distribution systems in cells.
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14
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Venkatesan V, Kumar R S, Kumar SA, Sahoo SK. Highly selective turn-on fluorogenic chemosensor for Zn2+ based on chelation enhanced fluorescence. INORG CHEM COMMUN 2019. [DOI: 10.1016/j.inoche.2019.02.020] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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15
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Kluska K, Adamczyk J, Krężel A. Metal binding properties, stability and reactivity of zinc fingers. Coord Chem Rev 2018. [DOI: 10.1016/j.ccr.2018.04.009] [Citation(s) in RCA: 109] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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16
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K.C. TB, Suga K, Isoshima T, Aigaki T, Ito Y, Shiba K, Uzawa T. Wash-free and selective imaging of epithelial cell adhesion molecule (EpCAM) expressing cells with fluorogenic peptide ligands. Biochem Biophys Res Commun 2018; 500:283-287. [DOI: 10.1016/j.bbrc.2018.04.059] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2018] [Accepted: 04/09/2018] [Indexed: 12/31/2022]
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17
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Singh MP, Baruah JB. Modulation of dual fluorescence modes and emissions of 2-(1,4-dioxo-1,4-dihydro-naphthalen-2-yl-amino)benzoic acid. J Mol Struct 2017. [DOI: 10.1016/j.molstruc.2017.08.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
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18
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Wang D, Chen W, Huang S, He Y, Liu X, Hu Q, Wei T, Sang H, Gan J, Chen H. Structural basis of Zn(II) induced metal detoxification and antibiotic resistance by histidine kinase CzcS in Pseudomonas aeruginosa. PLoS Pathog 2017; 13:e1006533. [PMID: 28732057 PMCID: PMC5540610 DOI: 10.1371/journal.ppat.1006533] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2017] [Revised: 08/02/2017] [Accepted: 07/14/2017] [Indexed: 11/19/2022] Open
Abstract
Pseudomonas aeruginosa (P. aeruginosa) is a major opportunistic human pathogen, causing serious nosocomial infections among immunocompromised patients by multi-determinant virulence and high antibiotic resistance. The CzcR-CzcS signal transduction system in P. aeruginosa is primarily involved in metal detoxification and antibiotic resistance through co-regulating cross-resistance between Zn(II) and carbapenem antibiotics. Although the intracellular regulatory pathway is well-established, the mechanism by which extracellular sensor domain of histidine kinase (HK) CzcS responds to Zn(II) stimulus to trigger downstream signal transduction remains unclear. Here we determined the crystal structure of the CzcS sensor domain (CzcS SD) in complex with Zn(II) at 1.7 Å resolution. This is the first three-dimensional structural view of Zn(II)-sensor domain of the two-component system (TCS). The CzcS SD is of α/β-fold in nature, and it senses the Zn(II) stimulus at micromole level in a tetrahedral geometry through its symmetry-related residues (His55 and Asp60) on the dimer interface. Though the CzcS SD resembles the PhoQ-DcuS-CitA (PDC) superfamily member, it interacts with the effector in a novel domain with the N-terminal α-helices rather than the conserved β-sheets pocket. The dimerization of the N-terminal H1 and H1’ α-helices is of primary importance for the activity of HK CzcS. This study provides preliminary insight into the molecular mechanism of Zn(II) sensing and signaling transduction by the HK CzcS, which will be beneficial to understand how the pathogen P. aeruginosa resists to high levels of heavy metals and antimicrobial agents. P. aeruginosa inhabits diverse environments and is one of the most prevalent opportunistic human pathogens of immunocompromised patients. The high antibiotic resistance is a major cause of therapeutic failure in the treatment of P. aeruginosa infections. The opportunistic pathogen P. aeruginosa co-regulates cross-resistance between Zn(II) and carbapenem antibiotics by the CzcR-CzcS signal transduction system. The extracellular Zn(II) stimulus is sensed by the HK CzcS and further triggers metal detoxification and antibiotic resistance through intracellular regulatory pathway. Here, we provide the three-dimensional structure of CzcS SD in complex with the Zn(II). Based on the structure, several key residues for Zn(II) sensing and regulation are identified, and the signal transduction is disclosed to be modulated by the dimerization of N-terminal α-helices in the sensor domain. Our research will provide potential guidance for the treatment of clinical issues caused by co-regulation between heavy metals and antibiotics in P. aeruginosa.
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Affiliation(s)
- Dan Wang
- Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Chemistry for Life Sciences, Nanjing University, Nanjing, P.R. China
| | - Weizhong Chen
- Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Chemistry for Life Sciences, Nanjing University, Nanjing, P.R. China
| | - Shanqing Huang
- Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Chemistry for Life Sciences, Nanjing University, Nanjing, P.R. China
| | - Yafeng He
- Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Chemistry for Life Sciences, Nanjing University, Nanjing, P.R. China
| | - Xichun Liu
- Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Chemistry for Life Sciences, Nanjing University, Nanjing, P.R. China
| | - Qingyuan Hu
- Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Chemistry for Life Sciences, Nanjing University, Nanjing, P.R. China
| | - Tianbiao Wei
- Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Chemistry for Life Sciences, Nanjing University, Nanjing, P.R. China
| | - Hong Sang
- Jinling Hospital, Department of Dermatology, Medical School of Nanjing University, Nanjing University, Nanjing, P. R. China
| | - Jianhua Gan
- State Key Laboratory of Genetic Engineering, Collaborative Innovation Center of Genetics and Development, Department of Physiology and Biophysics, School of Life Sciences, Fudan University, Shanghai, China
| | - Hao Chen
- Coordination Chemistry Institute and the State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Chemistry for Life Sciences, Nanjing University, Nanjing, P.R. China
- * E-mail:
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19
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Dai Z. Steric and Stereochemical Modulation in Pyridyl- and Quinolyl-Containing Ligands. Molecules 2016; 21:molecules21121647. [PMID: 27916967 PMCID: PMC6274402 DOI: 10.3390/molecules21121647] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2016] [Revised: 11/28/2016] [Accepted: 11/28/2016] [Indexed: 12/30/2022] Open
Abstract
Nitrogen-containing pyridine and quinoline are outstanding platforms on which excellent ionophores and sensors for metal ions can be built. Steric and stereochemical effects can be used to modulate the affinity and selectivity of such ligands toward different metal ions on the coordination chemistry front. On the signal transduction front, such effects can also be used to modulate optical responses of these ligands in metal sensing systems. In this review, steric modulation of achiral ligands and stereochemical modulation in chiral ligands, especially ionophores and sensors for zinc, copper, silver, and mercury, are examined using published structural and spectral data. Although it might be more challenging to construct chiral ligands than achiral ones, isotropic and anisotropic absorption signals from a single chiroptical fluorescent sensor provide not only detection but also differentiation of multiple analytes with high selectivity.
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Affiliation(s)
- Zhaohua Dai
- Department of Chemistry and Physical Sciences, Forensic Science Program, Pace University, 1 Pace Plaza, New York, NY 10038, USA.
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20
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Laitaoja M, Isoniemi S, Valjakka J, Mándity IM, Jänis J. Deciphering metal ion preference and primary coordination sphere robustness of a designed zinc finger with high-resolution mass spectrometry. Protein Sci 2016; 26:198-207. [PMID: 27750369 DOI: 10.1002/pro.3067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Revised: 10/13/2016] [Accepted: 10/13/2016] [Indexed: 11/10/2022]
Abstract
Small zinc finger (ZnF) motifs are promising molecular scaffolds for protein design owing to their structural robustness and versatility. Moreover, their characterization provides important insights into protein folding in general. ZnF motifs usually possess an exceptional specificity and high affinity towards Zn(II) ion to drive folding. While the Zn(II) ion is canonically coordinated by two cysteine and two histidine residues, many other coordination spheres also exist in small ZnFs, all having four amino acid ligands. Here we used high-resolution mass spectrometry to study metal ion binding specificity and primary coordination sphere robustness of a designed zinc finger, named MM1. Based on the results, MM1 possesses high specificity for zinc with sub-micromolar binding affinity. Surprisingly, MM1 retains metal ion binding affinity even in the presence of selective alanine mutations of the primary zinc coordinating amino acid residues.
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Affiliation(s)
- Mikko Laitaoja
- Department of Chemistry, University of Eastern Finland, Joensuu, FI-80101, Finland
| | - Sari Isoniemi
- Department of Chemistry, University of Eastern Finland, Joensuu, FI-80101, Finland
| | - Jarkko Valjakka
- BioMediTech, University of Tampere, Tampere, FI-33520, Finland
| | - István M Mándity
- Institute of Pharmaceutical Chemistry, University of Szeged, Szeged, H-6720, Hungary
| | - Janne Jänis
- Department of Chemistry, University of Eastern Finland, Joensuu, FI-80101, Finland
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21
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Feng L, Guo L, Wang X. Preparation, properties and applications in cell imaging and ions detection of conjugated polymer nanoparticles with alcoxyl bonding fluorene core. Biosens Bioelectron 2016; 87:514-521. [PMID: 27598853 DOI: 10.1016/j.bios.2016.08.114] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 08/29/2016] [Accepted: 08/31/2016] [Indexed: 01/02/2023]
Abstract
A novel conjugated polymer (PFP) comprised of fluorene, benzene and alcoxyl units was synthesized by a Suzuki coupling reaction between fluorene borate and dibromobenzene derivant. Due to its longer alcoxyl groups in the side chain, PFP polymer possesses good solubility in common organic solvents. Accordingly, conjugated polymer nanoparticles (CPNs) from PFP polymer were easily prepared by a re-precipitation method. A spherical structure of the CPNs with an average diameter of ~75nm was verified by dynamic light scattering (DLS) and scanning electron microscopy (SEM). The CPNs exhibit high photostability, good biocompatibility and low cytotoxicity. Based on these excellent properties, the CPNs as staining and labeling regents were used to cell imaging and located in the cytoplasm. Interestingly, the fluorescent probe based on CPNs displays high selectivity and sensitivity for Fe(III) in water because of the aggregation-induced fluorescence quenching action between CPNs and Fe(III). The contribution of the report lies in providing a new strategy for designing and developing CPNs-based probes, and applying in the interdisciplinary fields of chemistry, biology and material sciences.
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Affiliation(s)
- Liheng Feng
- School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, PR China.
| | - Lixia Guo
- School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, PR China
| | - Xiaoju Wang
- Institute of Molecular Science, Chemical Biology and Molecular Engineering, Laboratory of Education Ministry, Shanxi University, Taiyuan 030006, PR China.
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22
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Che W, Yu T, Jin D, Ren X, Zhu D, Su Z, Bryce MR. A simple oxazoline as fluorescent sensor for Zn 2+ in aqueous media. INORG CHEM COMMUN 2016. [DOI: 10.1016/j.inoche.2016.03.025] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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23
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Leite A, Silva AMG, Coutinho C, Cunha-Silva L, de Castro B, Rangel M. Design of a Water Soluble Fluorescent 3-Hydroxy-4-Pyridinone Ligand Active at Physiological pH Values. J Fluoresc 2016; 26:1773-85. [DOI: 10.1007/s10895-016-1869-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Accepted: 06/14/2016] [Indexed: 01/08/2023]
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24
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Galbács G, Szokolai H, Kormányos A, Metzinger A, Szekeres L, Marcu C, Peter F, Muntean C, Negrea A, Ciopec M, Jancsó A. Cd(II) Capture Ability of an Immobilized, Fluorescent Hexapeptide. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2016. [DOI: 10.1246/bcsj.20150333] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Gábor Galbács
- Department of Inorganic and Analytical Chemistry, University of Szeged
| | - Hajnalka Szokolai
- Department of Inorganic and Analytical Chemistry, University of Szeged
| | - Attila Kormányos
- Department of Inorganic and Analytical Chemistry, University of Szeged
| | - Anikó Metzinger
- Department of Inorganic and Analytical Chemistry, University of Szeged
| | - Levente Szekeres
- Department of Inorganic and Analytical Chemistry, University of Szeged
| | - Claudiu Marcu
- Faculty of Industrial Chemistry and Environmental Engineering, Politehnica University of Timisoara
| | - Francisc Peter
- Faculty of Industrial Chemistry and Environmental Engineering, Politehnica University of Timisoara
| | - Cornelia Muntean
- Faculty of Industrial Chemistry and Environmental Engineering, Politehnica University of Timisoara
| | - Adina Negrea
- Faculty of Industrial Chemistry and Environmental Engineering, Politehnica University of Timisoara
| | - Mihaela Ciopec
- Faculty of Industrial Chemistry and Environmental Engineering, Politehnica University of Timisoara
| | - Attila Jancsó
- Department of Inorganic and Analytical Chemistry, University of Szeged
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25
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Reddi AR, Pawlowska M, Gibney BR. Evaluation of the Intrinsic Zn(II) Affinity of a Cys3His1 Site in the Absence of Protein Folding Effects. Inorg Chem 2015; 54:5942-8. [DOI: 10.1021/acs.inorgchem.5b00718] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Amit R. Reddi
- Department of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive, Atlanta, Georgia 30332, United States
| | - Malgorzata Pawlowska
- Department of Chemistry, Brooklyn College, 2900 Bedford Avenue, Brooklyn, New York 11210, United States
| | - Brian R. Gibney
- Department of Chemistry, Brooklyn College, 2900 Bedford Avenue, Brooklyn, New York 11210, United States
- Ph.D. Program
in Chemistry, The Graduate Center of the City University of New York, 365 Fifth Avenue, New York, New York 10016, United States
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26
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Prisic S, Hwang H, Dow A, Barnaby O, Pan TS, Lonzanida JA, Chazin WJ, Steen H, Husson RN. Zinc regulates a switch between primary and alternative S18 ribosomal proteins in Mycobacterium tuberculosis. Mol Microbiol 2015; 97:263-80. [PMID: 25858183 DOI: 10.1111/mmi.13022] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/02/2015] [Indexed: 12/21/2022]
Abstract
The Mycobacterium tuberculosis genome encodes five putative 'alternative' ribosomal proteins whose expression is repressed at high Zn(2+) concentration. Each alternative protein has a primary homologue that is predicted to bind Zn(2+). We hypothesized that zinc triggers a switch between these paired homologous proteins and therefore chose one of these pairs, S18-1/S18-2, to study mechanisms of the predicted competition for their incorporation into ribosomes. Our data show that Zn(2+)-depletion causes accumulation of both S18-2 mRNA and protein. In contrast, S18-1 mRNA levels are unchanged to slightly elevated under Zn(2+)-limited conditions. However, the amount of S18-1 protein is markedly decreased. We further demonstrate that both S18 proteins interact with ribosomal protein S6, a committed step in ribosome biogenesis. Zn(2+) is absolutely required for the S18-1/S6 interaction while it is dispensable for S18-2/S6 dimer formation. These data suggest a model in which S18-1 is the dominant ribosome constituent in high zinc conditions, e.g. inside of phagosomes, but that it can be replaced by S18-2 when zinc is deficient, e.g. in the extracellular milieu. Consequently, Zn(2+)-depletion may serve as a signal for building alternative ribosomes when M. tuberculosis is released from macrophages, to allow survival in the extracellular environment.
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Affiliation(s)
- Sladjana Prisic
- Division of Infectious Diseases, Boston Children's Hospital/Harvard Medical School, Boston, MA.,Department of Microbiology, University of Hawaii at Manoa, Honolulu, HI
| | - Hyonson Hwang
- Department of Pathology, Boston Children's Hospital/Harvard Medical School, Boston, MA
| | - Allexa Dow
- Department of Microbiology, University of Hawaii at Manoa, Honolulu, HI
| | - Omar Barnaby
- Department of Pathology, Boston Children's Hospital/Harvard Medical School, Boston, MA
| | - Tenny S Pan
- Department of Microbiology, University of Hawaii at Manoa, Honolulu, HI
| | | | - Walter J Chazin
- Center for Structural Biology, Vanderbilt University, Nashville, TN, USA
| | - Hanno Steen
- Department of Pathology, Boston Children's Hospital/Harvard Medical School, Boston, MA
| | - Robert N Husson
- Division of Infectious Diseases, Boston Children's Hospital/Harvard Medical School, Boston, MA
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27
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Rodrigues AV, Kandegedara A, Rotondo JA, Dancis A, Stemmler TL. Iron loading site on the Fe-S cluster assembly scaffold protein is distinct from the active site. Biometals 2015; 28:567-76. [PMID: 25782577 DOI: 10.1007/s10534-015-9846-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Accepted: 03/05/2015] [Indexed: 11/30/2022]
Abstract
Iron-sulfur (Fe-S) cluster containing proteins are utilized in almost every biochemical pathway. The unique redox and coordination chemistry associated with the cofactor allows these proteins to participate in a diverse set of reactions, including electron transfer, enzyme catalysis, DNA synthesis and signaling within several pathways. Due to the high reactivity of the metal, it is not surprising that biological Fe-S cluster assembly is tightly regulated within cells. In yeast, the major assembly pathway for Fe-S clusters is the mitochondrial ISC pathway. Yeast Fe-S cluster assembly is accomplished using the scaffold protein (Isu1) as the molecular foundation, with assistance from the cysteine desulfurase (Nfs1) to provide sulfur, the accessory protein (Isd11) to regulate Nfs1 activity, the yeast frataxin homologue (Yfh1) to regulate Nfs1 activity and participate in Isu1 Fe loading possibly as a chaperone, and the ferredoxin (Yah1) to provide reducing equivalents for assembly. In this report, we utilize calorimetric and spectroscopic methods to provide molecular insight into how wt-Isu1 from S. cerevisiae becomes loaded with iron. Isothermal titration calorimetry and an iron competition binding assay were developed to characterize the energetics of protein Fe(II) binding. Differential scanning calorimetry was used to identify thermodynamic characteristics of the protein in the apo state or under iron loaded conditions. Finally, X-ray absorption spectroscopy was used to characterize the electronic and structural properties of Fe(II) bound to Isu1. Current data are compared to our previous characterization of the D37A Isu1 mutant, and these suggest that when Isu1 binds Fe(II) in a manner not perturbed by the D37A substitution, and that metal binding occurs at a site distinct from the cysteine rich active site in the protein.
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Affiliation(s)
- Andria V Rodrigues
- Departments of Biochemistry and Molecular Biology, Wayne State University, Detroit, MI, USA
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28
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Liu Q, Wang J, Boyd BJ. Peptide-based biosensors. Talanta 2015; 136:114-27. [PMID: 25702993 DOI: 10.1016/j.talanta.2014.12.020] [Citation(s) in RCA: 133] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2014] [Revised: 11/26/2014] [Accepted: 12/18/2014] [Indexed: 12/24/2022]
Abstract
Peptides have been used as components in biological analysis and fabrication of novel biosensors for a number of reasons, including mature synthesis protocols, diverse structures and as highly selective substrates for enzymes. Bio-conjugation strategies can provide an efficient way to convert interaction information between peptides and analytes into a measurable signal, which can be used for fabrication of novel peptide-based biosensors. Many sensitive fluorophores can respond rapidly to environmental changes and stimuli manifest as a change in spectral characteristics, hence environmentally-sensitive fluorophores have been widely used as signal markers to conjugate to peptides to construct peptide-based molecular sensors. Additionally, nanoparticles, fluorescent polymers, graphene and near infrared dyes are also used as peptide-conjugated signal markers. On the other hand, peptides may play a generalist role in peptide-based biosensors. Peptides have been utilized as bio-recognition elements to bind various analytes including proteins, nucleic acid, bacteria, metal ions, enzymes and antibodies in biosensors. The selectivity of peptides as an enzymatic substrate has thus been utilized to construct enzyme sensors or enzyme-activity sensors. In addition, progress on immobilization and microarray techniques of peptides has facilitated the progress and commercial application of chip-based peptide biosensors in clinical diagnosis.
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Affiliation(s)
- Qingtao Liu
- Drug Delivery Disposition and Dynamics-Monash Institute of Pharmaceutical Sciences, Monash University (Parkville Campus), 381 Royal Parade, Parkville 3052, VIC, Australia; ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, Monash Institute of Pharmaceutical Sciences, Monash University (Parkville Campus), 381 Royal Parade, Parkville 3052, VIC, Australia
| | - Jinfeng Wang
- Australian Future Fibres Research and Innovation Centre, Institute for Frontier Materials, Deakin University, Geelong 3217, VIC, Australia
| | - Ben J Boyd
- Drug Delivery Disposition and Dynamics-Monash Institute of Pharmaceutical Sciences, Monash University (Parkville Campus), 381 Royal Parade, Parkville 3052, VIC, Australia; ARC Centre of Excellence in Convergent Bio-Nano Science and Technology, Monash Institute of Pharmaceutical Sciences, Monash University (Parkville Campus), 381 Royal Parade, Parkville 3052, VIC, Australia.
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29
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Kushwaha AK, Deochand DK, Grove A. A moonlighting function of Mycobacterium smegmatis Ku in zinc homeostasis? Protein Sci 2014; 24:253-63. [PMID: 25450225 DOI: 10.1002/pro.2612] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Accepted: 11/25/2014] [Indexed: 01/14/2023]
Abstract
Ku protein participates in DNA double-strand break repair via the nonhomologous end-joining pathway. The three-dimensional structure of eukaryotic Ku reveals a central core consisting of a β-barrel domain and pillar and bridge regions that combine to form a ring-like structure that encircles DNA. Homologs of Ku are encoded by a subset of bacterial species, and they are predicted to conserve this core domain. In addition, the bridge region of Ku from some bacteria is predicted from homology modeling and sequence analyses to contain a conventional HxxC and CxxC (where x is any residue) zinc-binding motif. These potential zinc-binding sites have either deteriorated or been entirely lost in Ku from other organisms. Using an in vitro metal binding assay, we show that Mycobacterium smegmatis Ku binds two zinc ions. Zinc binding modestly stabilizes the Ku protein (by ∼3°C) and prevents cysteine oxidation, but it has little effect on DNA binding. In vivo, zinc induces significant upregulation of the gene encoding Ku (∼sixfold) as well as a divergently oriented gene encoding a predicted zinc-dependent MarR family transcription factor. Notably, overexpression of Ku confers zinc tolerance on Escherichia coli. We speculate that zinc-binding sites in Ku proteins from M. smegmatis and other mycobacterial species have been evolutionarily retained to provide protection against zinc toxicity without compromising the function of Ku in DNA double-strand break repair.
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Affiliation(s)
- Ambuj K Kushwaha
- Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana, 70803
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30
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Chan KL, Bakman I, Marts AR, Batir Y, Dowd TL, Tierney D, Gibney BR. Characterization of the Zn(II) binding properties of the human Wilms' tumor suppressor protein C-terminal zinc finger peptide. Inorg Chem 2014; 53:6309-20. [PMID: 24893204 PMCID: PMC4066921 DOI: 10.1021/ic500862b] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Indexed: 12/19/2022]
Abstract
Zinc finger proteins that bind Zn(II) using a Cys2His2 coordination motif within a ββα protein fold are the most abundant DNA binding transcription factor domains in eukaryotic systems. These classic zinc fingers are typically unfolded in the apo state and spontaneously fold into their functional ββα folds upon incorporation of Zn(II). These metal-induced protein folding events obscure the free energy cost of protein folding by coupling the protein folding and metal-ion binding thermodynamics. Herein, we determine the formation constant of a Cys2His2/ββα zinc finger domain, the C-terminal finger of the Wilms' tumor suppressor protein (WT1-4), for the purposes of determining its free energy cost of protein folding. Measurements of individual conditional dissociation constants, Kd values, at pH values from 5 to 9 were determined using fluorescence spectroscopy by direct or competition titration. Potentiometric titrations of apo-WT1-4 followed by NMR spectroscopy provided the intrinsic pKa values of the Cys2His2 residues, and corresponding potentiometric titrations of Zn(II)-WT1-4 followed by fluorescence spectroscopy yielded the effective pKa(eff) values of the Cys2His2 ligands bound to Zn(II). The Kd, pKa, and pKa(eff) values were combined in a minimal, complete equilibrium model to yield the pH-independent formation constant value for Zn(II)-WT1-4, Kf(ML) value of 7.5 × 10(12) M(-1), with a limiting Kd value of 133 fM. This shows that Zn(II) binding to the Cys2His2 site in WT1-4 provides at least -17.6 kcal/mol in driving force to fold the protein scaffold. A comparison of the conditional dissociation constants of Zn(II)-WT1-4 to those from the model peptide Zn(II)-GGG-Cys2His2 over the pH range 5.0 to 9.0 and a comparison of their pH-independent Kf(ML) values demonstrates that the free energy cost of protein folding in WT1-4 is less than +2.1 kcal/mol. These results validate our GGG model system for determining the cost of protein folding in natural zinc finger proteins and support the conclusion that the cost of protein folding in most zinc finger proteins is ≤+4.2 kcal/mol, a value that pales in comparison to the free energy contribution of Zn(II) binding, -17.6 kcal/mol.
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Affiliation(s)
- Ka Lam Chan
- Department of Chemistry, Brooklyn
College, 2900 Bedford
Avenue, Brooklyn, New York 11210, United States
| | - Inna Bakman
- Department of Chemistry, Brooklyn
College, 2900 Bedford
Avenue, Brooklyn, New York 11210, United States
- Ph.D. Program in Biochemistry, The City
University of New York, New York, New York 10016, United States
| | - Amy R. Marts
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Yuksel Batir
- Department of Chemistry, Brooklyn
College, 2900 Bedford
Avenue, Brooklyn, New York 11210, United States
| | - Terry L. Dowd
- Department of Chemistry, Brooklyn
College, 2900 Bedford
Avenue, Brooklyn, New York 11210, United States
- Ph.D. Program in Biochemistry, The City
University of New York, New York, New York 10016, United States
| | - David
L. Tierney
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Brian R. Gibney
- Department of Chemistry, Brooklyn
College, 2900 Bedford
Avenue, Brooklyn, New York 11210, United States
- Ph.D. Program in Biochemistry, The City
University of New York, New York, New York 10016, United States
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31
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Speight LC, Samanta M, Petersson EJ. Minimalist Approaches to Protein Labelling: Getting the Most Fluorescent Bang for Your Steric Buck. Aust J Chem 2014. [DOI: 10.1071/ch13554] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Fluorescence methods allow one to monitor protein conformational changes, protein–protein associations, and proteolysis in real time, at the single molecule level and in living cells. The information gained in such experiments is a function of the spectroscopic techniques used and the strategic placement of fluorophore labels within the protein structure. There is often a trade-off between size and utility for fluorophores, whereby large size can be disruptive to the protein’s fold or function, but valuable characteristics, such as visible wavelength absorption and emission or brightness, require sizable chromophores. Three major types of fluorophore readouts are commonly used: (1) Förster resonance energy transfer (FRET); (2) photoinduced electron transfer (PET); and (3) environmental sensitivity. This review focuses on those probes small enough to be incorporated into proteins during ribosomal translation, which allows the probes to be placed on the interiors of proteins as they are folded during synthesis. The most broadly useful method for doing so is site-specific unnatural amino acid (UAA) mutagenesis. We discuss the use of UAA probes in applications relying on FRET, PET, and environmental sensitivity. We also briefly review other methods of protein labelling and compare their relative merits to UAA mutagenesis. Finally, we discuss small probes that have thus far been used only in synthetic peptides, but which have unusual value and may be candidates for incorporation using UAA methods.
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32
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The Salmonella enterica ZinT structure, zinc affinity and interaction with the high-affinity uptake protein ZnuA provide insight into the management of periplasmic zinc. Biochim Biophys Acta Gen Subj 2013; 1840:535-44. [PMID: 24128931 DOI: 10.1016/j.bbagen.2013.10.010] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2013] [Revised: 09/17/2013] [Accepted: 10/07/2013] [Indexed: 11/22/2022]
Abstract
BACKGROUND In Gram-negative bacteria the ZnuABC transporter ensures adequate zinc import in Zn(II)-poor environments, like those encountered by pathogens within the infected host. Recently, the metal-binding protein ZinT was suggested to operate as an accessory component of ZnuABC in periplasmic zinc recruitment. Since ZinT is known to form a ZinT-ZnuA complex in the presence of Zn(II) it was proposed to transfer Zn(II) to ZnuA. The present work was undertaken to test this claim. METHODS ZinT and its structural relationship with ZnuA have been characterized by multiple biophysical techniques (X-ray crystallography, SAXS, analytical ultracentrifugation, fluorescence spectroscopy). RESULTS The metal-free and metal-bound crystal structures of Salmonella enterica ZinT show one Zn(II) binding site and limited structural changes upon metal removal. Spectroscopic titrations with Zn(II) yield a KD value of 22±2nM for ZinT, while those with ZnuA point to one high affinity (KD<20nM) and one low affinity Zn(II) binding site (KD in the micromolar range). Sedimentation velocity experiments established that Zn(II)-bound ZinT interacts with ZnuA, whereas apo-ZinT does not. The model of the ZinT-ZnuA complex derived from small angle X-ray scattering experiments points to a disposition that favors metal transfer as the metal binding cavities of the two proteins face each other. CONCLUSIONS ZinT acts as a Zn(II)-buffering protein that delivers Zn(II) to ZnuA. GENERAL SIGNIFICANCE Knowledge of the ZinT-ZnuA relationship is crucial for understanding bacterial Zn(II) uptake.
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Smith SJ, Du K, Radford RJ, Tezcan FA. Functional, metal-based crosslinkers for α-helix induction in short peptides. Chem Sci 2013; 4:3740-3747. [PMID: 24156013 PMCID: PMC3800689 DOI: 10.1039/c3sc50858g] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Many protein-protein interactions that play a central role in cellular processes involve α-helical domains. Consequently, there has been great interest in developing strategies for stabilizing short peptides in α-helical conformations toward the inhibition and interrogation of protein-protein interactions. Here, we show that tridentate Hybrid Coordination Motifs (HCMs), which consist of a natural (histidine, His) and an unnatural (8-hydroxyquinoline, Quin) metal binding functionality, can bind divalent metal ions with high affinity and thereby induce/stabilize an α-helical configuration in short peptide sequences. The Quin functionality is readily introduced onto peptide platforms both during or after solid-state peptide synthesis, demonstrating the preparative versatility of HCMs. A systematic study involving a series of HCM-bearing peptides has revealed the critical importance of the length of the linkage between the Quin moiety and the peptide backbone as well as the metal coordination geometry in determining the extent of α-helix induction. Through ZnII coordination or modification with ReI(Quin)(CO)3, the HCM-bearing peptides can be rendered luminescent in the visible region, thus showing that HCMs can be exploited to simultaneously introduce structure and functionality into short peptides.
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Affiliation(s)
- Sarah J Smith
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Dr., La Jolla, California 92093-0356
| | - Kang Du
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Dr., La Jolla, California 92093-0356
| | - Robert J Radford
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Dr., La Jolla, California 92093-0356
| | - F Akif Tezcan
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Dr., La Jolla, California 92093-0356
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34
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Srivastava P, Ali R, Razi SS, Shahid M, Patnaik S, Misra A. A simple blue fluorescent probe to detect Hg2+ in semiaqueous environment by intramolecular charge transfer mechanism. Tetrahedron Lett 2013. [DOI: 10.1016/j.tetlet.2013.05.014] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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35
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Zhuang YD, Chiang PY, Wang CW, Tan KT. Environment-Sensitive Fluorescent Turn-On Probes Targeting Hydrophobic Ligand-Binding Domains for Selective Protein Detection. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201302884] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
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36
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Zhuang YD, Chiang PY, Wang CW, Tan KT. Environment-sensitive fluorescent turn-on probes targeting hydrophobic ligand-binding domains for selective protein detection. Angew Chem Int Ed Engl 2013; 52:8124-8. [PMID: 23780746 DOI: 10.1002/anie.201302884] [Citation(s) in RCA: 158] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2013] [Revised: 05/27/2013] [Indexed: 12/15/2022]
Affiliation(s)
- Yu-De Zhuang
- Department of Chemistry, National Tsing Hua University, 101 Sec. 2, Kuang-Fu Rd., Hsinchu 30013, Taiwan, ROC
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37
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Stapleton B, Walker LR, Logan TM. Zn(II) stimulation of Fe(II)-activated repression in the iron-dependent repressor from Mycobacterium tuberculosis. Biochemistry 2013; 52:1927-38. [PMID: 23432191 DOI: 10.1021/bi301608p] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Thermodynamic measurements of Fe(II) binding and activation of repressor function in the iron-dependent repressor from Mycobacterium tuberculosis (IdeR) are reported. IdeR, a member of the diphtheria toxin repressor family of proteins, regulates iron homeostasis and contributes to the virulence response in M. tuberculosis. Although iron is the physiological ligand, this is the first detailed analysis of iron binding and activation in this protein. The results showed that IdeR binds 2 equiv of Fe(II) with dissociation constants that differ by a factor of 25. The high- and low-affinity iron binding sites were assigned to physical binding sites I and II, respectively, using metal binding site mutants. IdeR was also found to contain a high-affinity Zn(II) binding site that was assigned to physical metal binding site II through the use of binding site mutants and metal competition assays. Fe(II) binding was modestly weaker in the presence of Zn(II), but the coupled metal binding-DNA binding affinity was significantly stronger, requiring 30-fold less Fe(II) to activate DNA binding compared to Fe(II) alone. Together, these results suggest that IdeR is a mixed-metal repressor, where Zn(II) acts as a structural metal and Fe(II) acts to trigger the physiologically relevant promoter binding. This new model for IdeR activation provides a better understanding of IdeR and the biology of iron homeostasis in M. tuberculosis.
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Affiliation(s)
- Brian Stapleton
- Department of Chemistry and Biochemistry, 102 Varsity Way, Florida State University, Tallahassee, Florida 32306-4390, United States
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38
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Small-molecule fluorophores and fluorescent probes for bioimaging. Pflugers Arch 2013; 465:347-59. [DOI: 10.1007/s00424-013-1234-z] [Citation(s) in RCA: 180] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2012] [Revised: 01/31/2013] [Accepted: 01/31/2013] [Indexed: 12/14/2022]
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39
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Zeng HH, Matveeva EG, Stoddard AK, Fierke CA, Thompson RB. Long wavelength fluorescence ratiometric zinc biosensor. J Fluoresc 2013; 23:375-9. [PMID: 23345045 DOI: 10.1007/s10895-013-1161-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Accepted: 01/07/2013] [Indexed: 10/27/2022]
Abstract
A protein-based emission ratiometric fluorescence biosensor is described that exhibits sensitivity to free zinc ion in solution down to picomolar concentrations. Ratiometric measurements are widely used to assure accurate quantitation, and emission ratios are preferred for laser scanning microscopes such as confocal fluorescence microscopes. The relatively long emission wavelengths used are well suited to studies in tissues and other matrices which exhibit significant fluorescence background, and the apo-carbonic anhydrase moiety recognizes zinc ion with high and controllable specificity.
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Affiliation(s)
- Hui Hui Zeng
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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40
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Campanello GC, Ma Z, Grossoehme NE, Guerra AJ, Ward BP, Dimarchi RD, Ye Y, Dann CE, Giedroc DP. Allosteric inhibition of a zinc-sensing transcriptional repressor: insights into the arsenic repressor (ArsR) family. J Mol Biol 2013; 425:1143-57. [PMID: 23353829 DOI: 10.1016/j.jmb.2013.01.018] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2012] [Revised: 01/13/2013] [Accepted: 01/16/2013] [Indexed: 11/18/2022]
Abstract
The molecular basis of allosteric regulation remains a subject of intense interest. Staphylococcus aureus CzrA is a member of the ubiquitous arsenic repressor (ArsR) family of bacterial homodimeric metal-sensing proteins and has emerged as a model system for understanding allosteric regulation of operator DNA binding by transition metal ions. Using unnatural amino acid substitution and a standard linkage analysis, we show that a His97' NH(ε2)...O=C His67 quaternary structural hydrogen bond is an energetically significant contributor to the magnitude of the allosteric coupling free energy, ∆Gc. A "cavity" introduced just beneath this hydrogen bond in V66A/L68V CzrA results in a significant reduction in regulation by Zn(II) despite adopting a wild-type global structure and Zn(II) binding and DNA binding affinities only minimally affected from wild type. The energetics of Zn(II) binding and heterotropic coupling free energies (∆Hc, -T∆Sc) of the double mutant are also radically altered and suggest that increased internal dynamics leads to poorer allosteric negative regulation in V66A/L68V CzrA. A statistical coupling analysis of 3000 ArsR proteins reveals a sector that links the DNA-binding determinants and the α5 Zn(II)-sensing sites through V66/L68 in CzrA. We propose that distinct regulatory sites uniquely characteristic of individual ArsR proteins result from evolution of distinct connectivities to this sector, each capable of driving the same biological outcome, transcriptional derepression.
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41
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Radford RJ, Chyan W, Lippard SJ. Peptide-based Targeting of Fluorescent Zinc Sensors to the Plasma Membrane of Live Cells. Chem Sci 2013; 4:3080-3084. [PMID: 23878718 DOI: 10.1039/c3sc50974e] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Combining fluorescent zinc sensors with the facile syntheses and biological targeting capabilities of peptides, we created green- and blue-emitting probes that, (i) are readily prepared on the solid-phase, (ii) retain the photophysical and zinc-binding properties of the parent sensor, and (iii) can be directed to the extracellular side of plasma membranes in live cells for detection of mobile zinc.
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Affiliation(s)
- Robert J Radford
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139
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42
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Mbatia HW, Burdette SC. Photochemical Tools for Studying Metal Ion Signaling and Homeostasis. Biochemistry 2012; 51:7212-24. [DOI: 10.1021/bi3001769] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Hannah W. Mbatia
- University of Connecticut, 55 North Eagleville
Road, Storrs, Connecticut 06269-3060, United
States
| | - Shawn C. Burdette
- Worcester Polytechnic Institute, 100 Institute Road, Worcester, Massachusetts
01609-2280, United States
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43
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Misra A, Srivastava P, Shahid M. Fluorescent probe mimicking multiple logic gates and a molecular keypad lock upon interaction with Hg2+ and bovine serum albumin. Analyst 2012; 137:3470-8. [PMID: 22717541 DOI: 10.1039/c2an35561b] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The output fluorescence exhibited by an intramolecular charge transfer fluorescent probe 1 providing different chemical inputs mimicked multiple logic gates. A molecular keypad lock security device authorizing password entries (logic memory) and capable of solving crossword puzzles has been constructed by computing the output emission of 1 upon chemical inputs of BSA and Hg(2+). Based on logic operations the devised fluorescent keypad lock could be unlocked upon entering a correct sequence of password, 'BHU'.
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Affiliation(s)
- Arvind Misra
- Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi-221005, India. arvindmisra2003@ yahoo.com
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44
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Raimunda D, Long JE, Sassetti CM, Argüello JM. Role in metal homeostasis of CtpD, a Co²⁺ transporting P(1B4)-ATPase of Mycobacterium smegmatis. Mol Microbiol 2012; 84:1139-49. [PMID: 22591178 DOI: 10.1111/j.1365-2958.2012.08082.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Genetic studies in the tuberculosis mouse model have suggested that mycobacterial metal efflux systems, such as the P(1B4)-ATPase CtpD, are important for pathogenesis. The specificity for substrate metals largely determines the function of these ATPases; however, various substrates have been reported for bacterial and plant P(1B4)-ATPases leaving their function uncertain. Here we describe the functional role of the CtpD protein of Mycobacterium smegmatis. An M. smegmatis mutant strain lacking the ctpD gene was hypersensitive to Co²⁺ and Ni²⁺ and accumulated these metals in the cytoplasm. ctpD transcription was induced by both Co²⁺ and superoxide stress. Biochemical characterization of heterologously expressed, affinity-purified CtpD showed that this ATPase is activated by Co²⁺, Ni²⁺ and to a lesser extend Zn²⁺ (20% of maximum activity). The protein was also able to bind one Co²⁺, Ni²⁺ or Zn²⁺ to its transmembrane transport site. These observations indicate that CtpD is important for Co²⁺ and Ni²⁺ homeostasis in M. smegmatis, and that M. tuberculosis CtpD orthologue could be involved in metal detoxification and resisting cellular oxidative stress by modulating the intracellular concentration of these metals.
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Affiliation(s)
- Daniel Raimunda
- Department of Chemistry and Biochemistry, Worcester Polytechnic Institute, Worcester, MA, USA
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45
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Abstract
The intracellular availability of all biologically required transition metal ions in bacteria, e.g., Zn, Cu, Fe, as well as the detoxification of nonbiological heavy metal pollutants, is controlled at the molecular level by a panel of metalloregulatory or "metal sensor" proteins. Metal sensor proteins are specialized allosteric proteins that regulate the transcription of genes linked to transition metal homeostasis as a result of direct binding of a single metal ion or two closely related metal ions, to the exclusion of all others. In many cases, the binding of the cognate metal ion induces a structural change in a metal sensor oligomer that either activates or inhibits operator DNA binding. A quantitative measure of the degree to which a particular metal drives metalloregulation of transcription is the allosteric coupling-free energy, ΔG(c). In this chapter, we outline detailed spectroscopically derived methods for measuring metal binding affinity, K(Me), as well as ΔG(c) independent of K(Me), presented in the context of a simple coupled equilibrium scheme. Studies carried out in this way provide quantitative insights into the degree to which a particular metal ion is capable of driving allosteric switching, and via ligand substitution, the extent to which individual coordination bonds establish structural linkage of allosteric metal and operator DNA-binding sites.
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46
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Nishiyabu R, Kobayashi H, Kubo Y. Dansyl-containing boronate hydrogel film as fluorescent chemosensor of copper ions in water. RSC Adv 2012. [DOI: 10.1039/c2ra20516e] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
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47
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Alies B, Solari PL, Hureau C, Faller P. Dynamics of ZnII Binding as a Key Feature in the Formation of Amyloid Fibrils by Aβ11-28. Inorg Chem 2011; 51:701-8. [DOI: 10.1021/ic202247m] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Bruno Alies
- Laboratoire
de Chimie de Coordination
(LCC), CNRS, 205 route de Narbonne, 31077
Toulouse, France
- LCC, Université de Toulouse, UPS, INPT, 31077 Toulouse, France
| | - Pier-Lorenzo Solari
- Synchrotron SOLEIL, L’Orme des merisiers BP48, Saint-Aubin, F-91192 Gif-Sur-Yvette
Cedex, France
| | - Christelle Hureau
- Laboratoire
de Chimie de Coordination
(LCC), CNRS, 205 route de Narbonne, 31077
Toulouse, France
- LCC, Université de Toulouse, UPS, INPT, 31077 Toulouse, France
| | - Peter Faller
- Laboratoire
de Chimie de Coordination
(LCC), CNRS, 205 route de Narbonne, 31077
Toulouse, France
- LCC, Université de Toulouse, UPS, INPT, 31077 Toulouse, France
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Beck W. Metal Complexes of Biologically Important Ligands, CLXXVI.[1] Formation of Peptides within the Coordination Sphere of Metal Ions and of Classical and Organometallic Complexes and Some Aspects of Prebiotic Chemistry. Z Anorg Allg Chem 2011. [DOI: 10.1002/zaac.201100137] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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50
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Salgado EN, Brodin JD, To MM, Tezcan FA. Templated construction of a Zn-selective protein dimerization motif. Inorg Chem 2011; 50:6323-9. [PMID: 21648390 DOI: 10.1021/ic200746m] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Here, we report that the approach of metal-templated ligand synthesis can be applied to construct a dimeric protein assembly ((BMOE)RIDC1(2)), which is stabilized by noncovalent interactions and flexible covalent cross-linkers around the Zn templates. Despite its flexibility, (BMOE)RIDC1(2) selectively binds Zn(II) over other divalent metals and undergoes dimerization upon metal binding. Such simultaneous fulfillment of plasticity and selectivity is a hallmark of cellular signaling events that involve ligand/metal-induced protein dimerization.
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Affiliation(s)
- Eric N Salgado
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, MC 0356, La Jolla, California 92093, USA
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