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Fernandes CAH, Pazin WM, Dreyer TR, Bicev RN, Cavalcante WLG, Fortes-Dias CL, Ito AS, Oliveira CLP, Fernandez RM, Fontes MRM. Biophysical studies suggest a new structural arrangement of crotoxin and provide insights into its toxic mechanism. Sci Rep 2017; 7:43885. [PMID: 28256632 PMCID: PMC5335569 DOI: 10.1038/srep43885] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2016] [Accepted: 01/31/2017] [Indexed: 11/19/2022] Open
Abstract
Crotoxin (CTX) is the main neurotoxin found in Crotalus durissus rattlesnake venoms being composed by a nontoxic and non-enzymatic component (CA) and a toxic phospholipase A2 (CB). Previous crystallographic structures of CTX and CB provided relevant insights: (i) CTX structure showed a 1:1 molecular ratio between CA and CB, presenting three tryptophan residues in the CA/CB interface and one exposed to solvent; (ii) CB structure displayed a tetrameric conformation. This study aims to provide further information on the CTX mechanism of action by several biophysical methods. Our data show that isolated CB can in fact form tetramers in solution; however, these tetramers can be dissociated by CA titration. Furthermore, CTX exhibits a strong reduction in fluorescence intensity and lifetime compared with isolated CA and CB, suggesting that all tryptophan residues in CTX may be hidden by the CA/CB interface. By companying spectroscopy fluorescence and SAXS data, we obtained a new structural model for the CTX heterodimer in which all tryptophans are located in the interface, and the N-terminal region of CB is largely exposed to the solvent. Based on this model, we propose a toxic mechanism of action for CTX, involving the interaction of N-terminal region of CB with the target before CA dissociation.
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Affiliation(s)
- Carlos A. H. Fernandes
- Departamento de Física e Biofísica, Instituto de Biociências, Universidade Estadual Paulista, UNESP, Botucatu-SP, Brazil
| | - Wallance M. Pazin
- Departamento de Física, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, USP, Ribeirão Preto-SP, Brazil
| | - Thiago R. Dreyer
- Departamento de Física e Biofísica, Instituto de Biociências, Universidade Estadual Paulista, UNESP, Botucatu-SP, Brazil
| | - Renata N. Bicev
- Departamento de Física Experimental, Instituto de Física, Universidade de São Paulo – USP, São Paulo, SP, Brazil
| | - Walter L. G. Cavalcante
- Departamento de Física e Biofísica, Instituto de Biociências, Universidade Estadual Paulista, UNESP, Botucatu-SP, Brazil
- Departamento de Farmacologia, Instituto de Ciências Biológicas, UFMG, Belo Horizonte, MG, Brazil
| | - Consuelo L. Fortes-Dias
- Diretoria de Pesquisa e Desenvolvimento, Fundação Ezequiel Dias (FUNED), Belo Horizonte, MG, Brazil
| | - Amando S. Ito
- Departamento de Física, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, USP, Ribeirão Preto-SP, Brazil
| | - Cristiano L. P. Oliveira
- Departamento de Física Experimental, Instituto de Física, Universidade de São Paulo – USP, São Paulo, SP, Brazil
| | - Roberto Morato Fernandez
- Departamento de Física e Biofísica, Instituto de Biociências, Universidade Estadual Paulista, UNESP, Botucatu-SP, Brazil
| | - Marcos R. M. Fontes
- Departamento de Física e Biofísica, Instituto de Biociências, Universidade Estadual Paulista, UNESP, Botucatu-SP, Brazil
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2
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Brandao M, Iwakura R, Basilio F, Haleplian K, Ito A, de Freitas LCC, Bachmann L. Fluorescence lifetime of normal, benign, and malignant thyroid tissues. JOURNAL OF BIOMEDICAL OPTICS 2015; 20:067003. [PMID: 26085181 DOI: 10.1117/1.jbo.20.6.067003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Accepted: 05/19/2015] [Indexed: 05/20/2023]
Abstract
Fine-needle aspiration cytology is the standard technique to diagnose thyroid pathologies. However, this method results in a high percentage of inconclusive and false negatives. The use of time-resolved fluorescence techniques to detect biochemical composition and tissue structure alterations could help to develop a portable, minimally invasive, and nondestructive method to assist during surgical procedures. This study aimed to use fluorescence lifetimes to differentiate healthy and benign tissues from malignant thyroid tissue. The thyroid tissue was excited at 298-300 nm and the fluorescence decay registered at 340 and 450 nm. We observed fluorescence lifetimes at 340 nm emission of 0.80 ± 0.26 and 3.94 ± 0.47 ns for healthy tissue; 0.90 ± 0.24 and 4.05 ± 0.46 ns for benign lesions; and 1.21 ± 0.14 and 4.63 ± 0.25 ns for malignant lesions. For 450 nm emissions, we obtain lifetimes of 0.25 ± 0.18 and 3.99 ± 0.39 ns and for healthy tissue, 0.24 ± 0.17 and 4.20 ± 0.48 ns for benign lesions, 0.33 ± 0.32 and 4.55 ± 0.55 ns for malignant lesions. Employing analysis of variance, we differentiate malignant lesions from benign and healthy tissues. In addition, we use quadratic discriminant analysis to distinguish malignant from benign and healthy tissues with an accuracy of 76.1%, sensitivity of 74.7%, and specificity of 83.3%. These results indicate that time-resolved fluorescence can assist medical evaluation of thyroid pathologies during surgeries.
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Affiliation(s)
- Mariana Brandao
- Universidade de São Paulo, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Departamento de Física. Avenue Bandeirantes 3900, Ribeirão Preto, São Paulo 14040-901, Brazil
| | - Ricardo Iwakura
- Universidade de São Paulo, Faculdade de Medicina de Ribeirão Preto, Departamento de Oftalmo, Otorrino e Cirurgia de Cabeça e Pescoço, Avenue Bandeirantes 3900, Ribeirão Preto, São Paulo 14040-901, Brazil
| | - Fagne Basilio
- Universidade de São Paulo, Faculdade de Medicina de Ribeirão Preto, Departamento de Oftalmo, Otorrino e Cirurgia de Cabeça e Pescoço, Avenue Bandeirantes 3900, Ribeirão Preto, São Paulo 14040-901, Brazil
| | - Kaique Haleplian
- Universidade de São Paulo, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Departamento de Física. Avenue Bandeirantes 3900, Ribeirão Preto, São Paulo 14040-901, Brazil
| | - Amando Ito
- Universidade de São Paulo, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Departamento de Física. Avenue Bandeirantes 3900, Ribeirão Preto, São Paulo 14040-901, Brazil
| | - Luiz Carlos Conti de Freitas
- Universidade de São Paulo, Faculdade de Medicina de Ribeirão Preto, Departamento de Oftalmo, Otorrino e Cirurgia de Cabeça e Pescoço, Avenue Bandeirantes 3900, Ribeirão Preto, São Paulo 14040-901, Brazil
| | - Luciano Bachmann
- Universidade de São Paulo, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Departamento de Física. Avenue Bandeirantes 3900, Ribeirão Preto, São Paulo 14040-901, Brazil
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3
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Optical Characterization of Normal, Benign, and Malignant Thyroid Tissue: A Pilot Study. J Fluoresc 2015; 25:465-71. [DOI: 10.1007/s10895-015-1542-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2014] [Accepted: 02/23/2015] [Indexed: 10/23/2022]
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4
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Domingues TM, Buri MV, Daffre S, Campana PT, Riske KA, Miranda A. Structure-activity relationship of Trp-containing analogs of the antimicrobial peptide gomesin. J Pept Sci 2014; 20:421-8. [DOI: 10.1002/psc.2632] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2013] [Revised: 02/14/2014] [Accepted: 03/04/2014] [Indexed: 11/10/2022]
Affiliation(s)
- Tatiana M. Domingues
- Department of Biophysics; Federal University of Sao Paulo; Sao Paulo 04044-020 Brazil
| | - Marcus V. Buri
- Department of Biophysics; Federal University of Sao Paulo; Sao Paulo 04044-020 Brazil
| | - Sirlei Daffre
- Department of Parasitology, Institute of Biomedical Sciences; University of Sao Paulo; Sao Paulo Brazil 05508-900
| | - Patricia T. Campana
- School of Arts, Sciences and Humanities; University of Sao Paulo; Sao Paulo Brazil 03828-000
| | - Karin A. Riske
- Department of Biophysics; Federal University of Sao Paulo; Sao Paulo 04044-020 Brazil
| | - Antonio Miranda
- Department of Biophysics; Federal University of Sao Paulo; Sao Paulo 04044-020 Brazil
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5
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Interaction of a synthetic antimicrobial peptide with model membrane by fluorescence spectroscopy. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2013; 42:819-31. [DOI: 10.1007/s00249-013-0930-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Revised: 08/14/2013] [Accepted: 09/17/2013] [Indexed: 10/26/2022]
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6
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Ming Yang C. Biometal binding-site mimicry with modular, hetero-bifunctionally modified architecture encompassing a Trp/His motif: Insights into spatiotemporal noncovalent interactions from a comparative spectroscopic study. Dalton Trans 2011; 40:3008-27. [DOI: 10.1039/c0dt00237b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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7
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Fluorescence spectroscopy of small peptides interacting with microheterogeneous micelles. Int J Pharm 2010; 383:154-6. [DOI: 10.1016/j.ijpharm.2009.09.017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2009] [Accepted: 09/04/2009] [Indexed: 11/21/2022]
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8
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Romani AP, Ito AS. Interaction of adrenocorticotropin peptides with microheterogeneous systems — A fluorescence study. Biophys Chem 2009; 139:92-8. [DOI: 10.1016/j.bpc.2008.10.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2008] [Revised: 10/20/2008] [Accepted: 10/22/2008] [Indexed: 11/28/2022]
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9
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Romani AP, Marquezin CA, Soares AEE, Ito AS. Study of the interaction between Apis mellifera venom and micro-heterogeneous systems. J Fluoresc 2006; 16:423-30. [PMID: 16791506 DOI: 10.1007/s10895-006-0077-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2005] [Accepted: 01/23/2006] [Indexed: 10/24/2022]
Abstract
The bee venom, used in treatment of inflammatory and articular diseases, is a complex mixture of peptides and enzymes and the presence of tryptophan allows the investigation by fluorescence techniques. Steady state and time-resolved fluorescence spectroscopy were used to study the interaction between bee venom extracted from Apis mellifera and three micro heterogeneous systems: sodium dodecylsulphate (SDS) micelles, sodium dodecylsulphate-poly(ethylene oxide) (SDS-PEO) aggregates, and the polymeric micelles LUTROL F127, formed by poly(ethylene oxide)-poly(propylene oxide)- poly(ethylene oxide). Fluorescence parameters in buffer solution were typical of peptides containing tryptophan exposed to the aqueous medium, and they gradually changed upon the addition of surfactant and polymeric micelles, demonstrating the interaction of the peptides with the micro heterogeneous systems. Quenching experiments were carried out using the N-alkylpyridinium ions (ethyl, hexyl, and dodecyl) as quenchers. In buffer solution the quenching has low efficiency and is independent of the alkyl chain length of the quencher. In the presence of the micro heterogeneous systems the extent of static and dynamic quenching enhanced, showing that both fluorophore and quenchers reside in the microvolume of the aggregates. The more hydrophobic quencher (dodecyl pyridinium ion) provides higher values for K (SV) and dynamic quenching constants, and SDS-PEO aggregates are most efficient to promote interaction between peptides and alkyl pyridinium ions. The results proved that bee venom interacts with drug delivery micelles of the copolymer LUTROL F127.
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Affiliation(s)
- Ana Paula Romani
- Departamento de Física e Matemática, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brazil
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10
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Fernandez RM, Vieira RFF, Nakaie CR, Lamy MT, Ito AS. Acid-base titration of melanocortin peptides: evidence of Trp rotational conformers interconversion. Biopolymers 2005; 80:643-50. [PMID: 15657882 DOI: 10.1002/bip.20210] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Tryptophantime-resolved fluorescence was used to monitor acid-base titration properties of alpha-melanocyte stimulating hormone (alpha-MSH) and the biologically more potent analog [Nle4, D-Phe7]alpha -MSH (NDP-MSH), labeled or not with the paramagnetic amino acid probe 2,2,6,6-tetramthylpiperidine-N-oxyl-4-amino-4-carboxylic acid (Toac). Global analysis of fluorescence decay profiles measured in the pH range between 2.0 and 11.0 showed that, for each peptide, the data could be well fitted to three lifetimes whose values remained constant. The less populated short lifetime component changed little with pH and was ascribed to Trp g+ chi1 rotamer, in which electron transfer deactivation predominates over fluorescence. The long and intermediate lifetime preexponential factors interconverted along that pH interval and the result was interpreted as due to interconversion between Trp g- and trans chi1 rotamers, driven by conformational changes promoted by modifications in the ionization state of side-chain residues. The differences in the extent of interconversion in alpha-MSH and NDP-MSH are indicative of structural differences between the peptides, while titration curves suggest structural similarities between each peptide and its Toac-labeled species, in aqueous solution. Though less sensitive than fluorescence, the Toac electron spin resonance (ESR) isotropic hyperfine splitting parameter can also monitor the titration of side-chain residues located relatively far from the probe.
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11
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Volcov F, Goldman C. The efficiency of photolyase and indole complexes to repair DNA containing dimers of pyrimidine: A theoretical analysis of the electron transfer reactions. J Chem Phys 2004; 120:3381-6. [PMID: 15268493 DOI: 10.1063/1.1640612] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We analyze the effects of competing reactions to the efficiency of enzymatic splitting of pyrimidine dimers formed in DNA by the incidence of ultraviolet radiation. This is accomplished with the aid of a formula that expresses the efficiency of the repair in terms of parameters that regulate the reaction rates for primary and for back long-range electron transfers taking place in the process. Comparison of experimental data with estimations on account of this formula supports early conjectures in the literature that attribute the relative high performance of the enzymatic complexes of photolyase to its ability to suppress the back reaction.
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Affiliation(s)
- Flavia Volcov
- Instituto de Fisica, Universidade de Sao Paulo, CP 66318, 05315-970, Sao Paulo, Brazil
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12
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Marquezin CA, Hirata IY, Juliano L, Ito AS. Tryptophan as a probe for acid-base equilibria in peptides. Biopolymers 2004; 71:569-76. [PMID: 14635097 DOI: 10.1002/bip.10535] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We present results of time resolved fluorescence measurements performed in Tryptophan (Trp) derivatives and Trp-containing peptides in the pH range 3.0-11.0. For each compound a set of decay profiles measured in a given range of pH values was examined as a whole, using the global analysis technique. The data were fitted to two or three lifetime components and the analysis allowed the monitoring of the changes in the concentration of the different species contributing to the total fluorescence in that pH interval. The decay components were sensitive to the ionization state of groups neighboring the indol ring, and pK values for the equilibrium between protonated and deprotonated species were obtained from the preexponential factor of the lifetime components. In Trp, protonation of the amino terminal of the rotamer having electron transfer rate comparable to fluorescence decay rates was responsible for the interconvertion of a long lifetime component, to the 2.9 ns component usually observed in neutral pH. Trpbond;X peptides also have a single rotamer dominating the decay that is quenched by NH(3) (+). X-Trp peptides seem to be conformationally less restricted, and it is possible that rotamers interconvertion occur in high pH, increasing the population of nonquenched rotamers. Interconvertion between rotameric conformations of Trp are also present in the titration of ionizable groups in the side chain of peptides like His-Trp and Glu-Trp and control of pH is essential to the correct interpretation of fluorescence data in the study of peptides having such groups near to the Trp residue.
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13
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Hellings M, De Maeyer M, Verheyden S, Hao Q, Van Damme EJM, Peumans WJ, Engelborghs Y. The dead-end elimination method, tryptophan rotamers, and fluorescence lifetimes. Biophys J 2003; 85:1894-902. [PMID: 12944302 PMCID: PMC1303361 DOI: 10.1016/s0006-3495(03)74617-7] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2002] [Accepted: 05/30/2003] [Indexed: 11/17/2022] Open
Abstract
The Dead-End Elimination method was used to identify 40 low energy microconformations of 16 tryptophan residues in eight proteins. Single Trp-mutants of these proteins all show a double- or triple-exponential fluorescence decay. For ten of these lifetimes the corresponding rotameric state could be identified by comparing the bimolecular acrylamide quenching constant (k(q)) and the relative solvent exposure of the side chain in that microstate. In the absence of any identifiable quencher, the origin of the lifetime heterogeneity is interpreted in terms of the electron transfer process from the indole C epsilon 3 atom to the carbonyl carbon of the peptide bond. Therefore it is expected that a shorter [C epsilon 3-C[double bond]O] distance leads to a shorter lifetime as observed for these ten rotamers. Applying the same rule to the other 30 lifetimes, a link with their corresponding rotameric state could also be made. In agreement with the theory of Marcus and Sutin, the nonradiative rate constant shows an exponential relationship with the [C epsilon 3-C[double bond]O] distance for the 40 datapoints.
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Affiliation(s)
- Mario Hellings
- Laboratory of Biomolecular Dynamics, Catholic University of Leuven, Heverlee, Belgium
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14
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Engelborghs Y. The analysis of time resolved protein fluorescence in multi-tryptophan proteins. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2001; 57:2255-2270. [PMID: 11603842 DOI: 10.1016/s1386-1425(01)00485-1] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
In the last decades, considerable progress has been made in the analysis of the fluorescence decay of proteins with more than one tryptophan. The construction of single tryptophan containing proteins has shown that the lifetimes of the wild type proteins are often the linear combinations of the family lifetimes of the contributing tryptophan residues. Additivity is not followed when energy transfer takes place among tryptophan residues or when the structure of the remaining protein is altered upon the modification. Progress has also been made in the interpretation of the value of the lifetime and the linkage with the immediate environment. Probably all the irreversible processes leading to return to the ground state have been catalogued and their rate constants are documented. Also, the process of electron transfer to the peptide carbonyl is becoming more and more documented and is linked to the rotameric state of tryptophan. Reversible excited state processes are also being considered, including reversible interconversions between rotamers. Interesting information about tryptophan and its environment comes also from anisotropy measurements for proteins in the native, the denatured and the molten globule states. Alterations of protein fluorescence due to the effects of ligand binding or side chain modifications can be analyzed via the ratio of the quantum yields of the modified protein and the reference state. Using the ratio of quantum yields and the (amplitude weighted) average lifetime, three factors can be identified: (1) a change in the apparent radiative rate constant reflecting either static quenching or an intrinsic change in the radiative properties; (2) a change in dynamic quenching; and (3) a change in the balance of the populations of the microstates or local static quenching.
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Affiliation(s)
- Y Engelborghs
- Laboratory of Biomolecular Dynamics, University of Leuven, Belgium.
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Malicka J, Groth M, Karolczak J, Czaplewski C, Liwo A, Wiczk W. Influence of solvents and leucine configuration at position 5 on tryptophan fluorescence in cyclic enkephalin analogues. Biopolymers 2001; 58:447-57. [PMID: 11180057 DOI: 10.1002/1097-0282(20010405)58:4<447::aid-bip1020>3.0.co;2-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The fluorescence decay of tryptophan is a sensitive indicator of its local environment within a peptide or protein. In this study we carried out fluorescence measurements of the tryptophan residue of cyclic enkephalin analogues of a general formula X-c[D-Dab(2)-Gly(3)-Trp(4)-Y(5)] where X = Cbz or H and Y = D- or L-Leu, in four solvents [water, methanol, acetonitrile, and dimethyl sulfoxide (DMSO)]. An analysis of the tryptophan fluorescence decays using a discrete-exponential model indicates that tryptophan fluorescence decay can be described by a double exponential function in all solvents studied. Lifetime distribution analysis yields a bimodal distribution in protic solvents (water and methanol), whereas an asymmetric, unimodal distribution in an aprotic solvent (DMSO) and uni- or bimodal distributions in acetonitrile solution, depending on leucine configuration. The data are interpreted in terms of the rotamer model, in which the modality and the relative proportions of the lifetime components are related to the population distribution of tryptophan chi(1) rotamers about the C(alpha)--C(beta) bond. The chirality of the Leu(5) residue and solvent properties affect the local environment of the tryptophan residue and therefore influence the distribution of side-chain rotamers. These results are consistent with the results of theoretical conformational calculations.
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Affiliation(s)
- J Malicka
- University of Gdańsk, Faculty of Chemistry, Sobieskiego 18, 80-952 Gdańsk, Poland
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16
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Rzeska A, Malicka J, Stachowiak K, Szymańska A, Łankiewicz L, Wiczk W. Photophysics of phenylalanine analogues. J Photochem Photobiol A Chem 2001. [DOI: 10.1016/s1010-6030(01)00394-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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17
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Weinkauf R, Schiedt J. Energetics of photoinduced electron transfer in the indole.O2 cluster in gas phase: possible consequences for photoexcited tryptophan in solution. Photochem Photobiol 1997; 66:569-75. [PMID: 9383986 DOI: 10.1111/j.1751-1097.1997.tb03191.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
A direct process for an activationless electron transfer from photoexcited tryptophan to molecular oxygen is proposed. By photodetachment of mass-selected indole+.O2- clusters in gas phase a neutral indole+.O2- charge-separated exciplex state is found at 2.25 +/- 0.2 eV above the neutral ground state. By theory also, the existence of an excited charge separated state at 3.05 +/- 0.2 eV is postulated. In gas phase both charge-separated cluster states are energetically below the first singlet states 1Lb and 1La and the lower even below the first triplet state T1 of indole. In gas-phase clusters these energetics imply a very efficient quenching of photoexcited indole by fast electron transfer to oxygen. We discuss a similar mechanism for tryptophan.O2 in aqueous environment and find it without activation barrier and presumably extremely fast. In the collisional tryptophan*-O2 complex the efficiency and the time scale of the charge transfer process should be mostly solvent independent. In polar solvent a complete charge separation and free superoxide formation are expected. We correlate this model with previous fluorescence and phosphorescence quenching data of excited tryptophan by O2 and propose electron transfer to be the relevant process.
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Affiliation(s)
- R Weinkauf
- Institut für Physikalische und Theoretische Chemie, Technischen Universität München, Garching, Germany.
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