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Zeltser G, Sukhanov IM, Nevorotin AJ. MMM - The molecular model of memory. J Theor Biol 2022; 549:111219. [PMID: 35810778 DOI: 10.1016/j.jtbi.2022.111219] [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: 12/04/2021] [Revised: 07/01/2022] [Accepted: 07/04/2022] [Indexed: 11/17/2022]
Abstract
Identifying mechanisms underlying neurons ability to process information including acquisition, storage, and retrieval plays an important role in the understanding of the different types of memory, pathogenesis of many neurological diseases affecting memory and therapeutic target discovery. However, the traditional understanding of the mechanisms of memory associated with the electrical signals having a unique combination of frequency and amplitude does not answer the question how the memories can survive for life-long periods of time, while exposed to synaptic noise. Recent evidence suggests that, apart from neuronal circuits, a diversity of the molecular memory (MM) carriers, are essential for memory performance. The molecular model of memory (MMM) is proposed, according to which each item of incoming information (the elementary memory item - eMI) is encoded by both circuitries, with the unique for a given MI electrical parameters, and also the MM carriers, unique by its molecular composition. While operating as the carriers of incoming information, the MMs, are functioning within the neuron plasma membrane. Inactive (latent) initially, during acquisition each of the eMIs is activated to become a virtual copy of some real fact or events bygone. This activation is accompanied by the considerable remodeling of the MM molecule associated with the resonance effect.
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Affiliation(s)
| | - Ilya M Sukhanov
- Lab. Behavioral Pharmacology, Dept. Psychopharmacology, Valdman Institute of Pharmacology, I.P. Pavlov Medical University, Leo Tolstoi Street 6/8, St. Petersburg 197022, The Russian Federation
| | - Alexey J Nevorotin
- Laboratory of Electron Microscopy, I.P. Pavlov Medical University, Leo Tolstoi Street 6/8, St. Petersburg 197022, The Russian Federation
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2
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Petazzi RA, Aji AK, Chiantia S. Fluorescence microscopy methods for the study of protein oligomerization. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2020; 169:1-41. [DOI: 10.1016/bs.pmbts.2019.12.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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3
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Lolli G, Raboni S, Pasqualetto E, Benoni R, Campanini B, Ronda L, Mozzarelli A, Bettati S, Battistutta R. Insight into GFPmut2 pH Dependence by Single Crystal Microspectrophotometry and X-ray Crystallography. J Phys Chem B 2018; 122:11326-11337. [PMID: 30179482 DOI: 10.1021/acs.jpcb.8b07260] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The fluorescence of Green Fluorescent Protein (wtGFP) and variants has been exploited in distinct applications in cellular and analytical biology. GFPs emission depends on the population of the protonated (A-state) and deprotonated (B-state) forms of the chromophore. Whereas wtGFP is pH-independent, mutants in which Ser65 is replaced by either threonine or alanine (as in GFPmut2) are pH-dependent, with a p Ka around 6. Given the wtGFP pH-independence, only the structure of the protonated form was determined. The deprotonated form was deduced on the basis of the crystal structure of the Ser65Thr mutant at basic pH, assuming that it corresponds to the conformation populated in solution. Here, we present an investigation where structures of the protonated and deprotonated forms of GFPmut2 were determined from crystals grown in either MPD at pH 6 or PEG at pH 8.5, and moved to either higher or lower pH. Both crystal forms of GFPmut2 were titrated monitoring the process via polarized absorption microspectrophotometry in order to precisely correlate the protonation process with the structures. We found that (i) in solution, chromophore titration is not thermodynamically coupled with any residue and Glu222 is always protonated independent of the protonation state of the chromophore; (ii) the lack of coupling is reflected in the structural behavior of the chromophore and Glu222 environments, with only the former showing variations with pH; (iii) titrations of low-pH and high-pH grown crystals exhibit a Hill coefficient of about 0.75, indicating an anticooperative behavior not observed in solution; (iv) structures where pH was changed in the crystal point to Glu222 as the ionizable group responsible for the outset of the anticooperative behavior; and (v) in GFPmut2 the canonical GFP proton wire involving the chromophore is not interrupted at the level of Ser205 and Glu222 at basic pH as in the Ser65Thr mutant. This allows proposing the structure of the deprotonated state of GFPmut2 as an alternative model for the analogous state of wtGFP.
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Affiliation(s)
- Graziano Lolli
- Centro di Biologia Integrata - CIBIO , Università di Trento , 38123 Povo , Trento , Italy
| | - Samanta Raboni
- Dipartimento di Scienze degli Alimenti e del Farmaco , Università di Parma , 43124 Parma , Italy
| | - Elisa Pasqualetto
- Dipartimento di Scienze Chimiche , Università degli Studi di Padova and Istituto di Chimica Biomolecolare, Consiglio Nazionale delle Ricerche , 35131 Padua , Italy
| | - Roberto Benoni
- Dipartimento di Medicina e Chirurgia , Università di Parma , 43125 Parma , Italy
| | - Barbara Campanini
- Dipartimento di Scienze degli Alimenti e del Farmaco , Università di Parma , 43124 Parma , Italy
| | - Luca Ronda
- Dipartimento di Medicina e Chirurgia , Università di Parma , 43125 Parma , Italy
| | - Andrea Mozzarelli
- Dipartimento di Scienze degli Alimenti e del Farmaco , Università di Parma , 43124 Parma , Italy.,Istituto di Biofisica , Consiglio Nazionale delle Ricerche , 56124 Pisa , Italy.,Istituto Nazionale Biostrutture e Biosistemi , 00136 Rome , Italy
| | - Stefano Bettati
- Dipartimento di Medicina e Chirurgia , Università di Parma , 43125 Parma , Italy.,Istituto Nazionale Biostrutture e Biosistemi , 00136 Rome , Italy
| | - Roberto Battistutta
- Dipartimento di Scienze Chimiche , Università degli Studi di Padova and Istituto di Chimica Biomolecolare, Consiglio Nazionale delle Ricerche , 35131 Padua , Italy
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4
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Nandi S, Ghosh S, Bhattacharyya K. Live Cell Microscopy: A Physical Chemistry Approach. J Phys Chem B 2018; 122:3023-3036. [PMID: 29389140 DOI: 10.1021/acs.jpcb.7b11689] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Probing dynamics of intracellular components using physical chemistry techniques is a remarkable bottom-up approach for understanding the structures and functions of a biological cell. In this "Feature Article", we give an overview on local polarity, solvation, viscosity, acid-base property, red-ox processes (thiol-disulfide exchange), and gene silencing at selected intracellular components inside a live cell. Significant differences have been observed between cancer cells and their noncancer counterparts. We demonstrate that thiol-disulfide exchange, calcium oscillation, and gene silencing are manifested in time dependence of fluorescence intensity. We show that fluorescent gold nanoclusters may be used in drug delivery (e.g., doxorubicin) and selective killing of cancer cells. Further, we discuss dynamics and structural changes of DNA quadruplexes and i-motifs, induced by different external conditions (e.g., pH) and additives (e.g., K+ and other target specific small molecules). We demonstrate that peptidomimetic analogues have high specificity over double-stranded DNA for binding with i-motifs and G-quadruplexes. These results may have significant biological implications.
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Affiliation(s)
- Somen Nandi
- Department of Physical Chemistry , Indian Association for the Cultivation of Science , Jadavpur, Kolkata 700 032 , India
| | - Surajit Ghosh
- Organic & Medicinal Chemistry Division , CSIR-Indian Institute of Chemical Biology , 4, Raja S. C. Mullick Road , Jadavpur, Kolkata , 700 032 West Bengal , India.,Academy of Scientific and Innovative Research (AcSIR) , CSIR-Indian Institute of Chemical Biology Campus , 4 Raja S. C. Mullick Road , Jadavpur, Kolkata 700 032 , India
| | - Kankan Bhattacharyya
- Department of Chemistry , Indian Institute of Science Education and Research Bhopal , Bhopal , 462 066 Madhya Pradesh , India
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5
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Lin H, Yuan JM. Stochastic dynamic study of optical transition properties of single GFP-like molecules. J Biol Phys 2016; 42:271-97. [PMID: 26841730 DOI: 10.1007/s10867-015-9407-y] [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: 08/28/2015] [Accepted: 12/11/2015] [Indexed: 10/22/2022] Open
Abstract
Due to high fluctuations and quantum uncertainty, the processes of single-molecules should be treated by stochastic methods. To study fluorescence time series and their statistical properties, we have applied two stochastic methods, one of which is an analytic method to study the off-time distributions of certain fluorescence transitions and the other is Gillespie's method of stochastic simulations. These methods have been applied to study the optical transition properties of two single-molecule systems, GFPmut2 and a Dronpa-like molecule, to yield results in approximate agreement with experimental observations on these systems. Rigorous oscillatory time series of GFPmut2 before it unfolds in the presence of denaturants have not been obtained based on the stochastic method used, but, on the other hand, the stochastic treatment puts constraints on the conditions under which such oscillatory behavior is possible. Furthermore, a sensitivity analysis is carried out on GFPmut2 to assess the effects of transition rates on the observables, such as fluorescence intensities.
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Affiliation(s)
- Hanbing Lin
- Department of Physics, Drexel University, Philadelphia, PA, 19104, USA
| | - Jian-Min Yuan
- Department of Physics, Drexel University, Philadelphia, PA, 19104, USA.
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6
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In cellulo evaluation of phototransformation quantum yields in fluorescent proteins used as markers for single-molecule localization microscopy. PLoS One 2014; 9:e98362. [PMID: 24915511 PMCID: PMC4051587 DOI: 10.1371/journal.pone.0098362] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Accepted: 05/01/2014] [Indexed: 11/19/2022] Open
Abstract
Single-molecule localization microscopy of biological samples requires a precise knowledge of the employed fluorescent labels. Photoactivation, photoblinking and photobleaching of phototransformable fluorescent proteins influence the data acquisition and data processing strategies to be used in (Fluorescence) Photoactivation Localization Microscopy ((F)-PALM), notably for reliable molecular counting. As these parameters might depend on the local environment, they should be measured in cellulo in biologically relevant experimental conditions. Here, we measured phototransformation quantum yields for Dendra2 fused to actin in fixed mammalian cells in typical (F)-PALM experiments. To this aim, we developed a data processing strategy based on the clustering optimization procedure proposed by Lee et al (PNAS 109, 17436–17441, 2012). Using simulations, we estimated the range of experimental parameters (molecular density, molecular orientation, background level, laser power, frametime) adequate for an accurate determination of the phototransformation yields. Under illumination at 561 nm in PBS buffer at pH 7.4, the photobleaching yield of Dendra2 fused to actin was measured to be (2.5±0.4)×10−5, whereas the blinking-off yield and thermally-activated blinking-on rate were measured to be (2.3±0.2)×10−5 and 11.7±0.5 s−1, respectively. These phototransformation yields differed from those measured in poly-vinyl alcohol (PVA) and were strongly affected by addition of the antifading agent 1,4-diazabicyclo[2.2.2]octane (DABCO). In the presence of DABCO, the photobleaching yield was reduced 2-fold, the blinking-off yield was decreased more than 3-fold, and the blinking-on rate was increased 2-fold. Therefore, DABCO largely improved Dendra2 photostability in fixed mammalian cells. These findings are consistent with redox-based bleaching and blinking mechanisms under (F)-PALM experimental conditions. Finally, the green-to-red photoconversion quantum yield of Dendra2 was estimated to be (1.4±0.6)×10−5in cellulo under 405 nm illumination.
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7
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Chattoraj S, Saha S, Jana SS, Bhattacharyya K. Dynamics of Gene Silencing in a Live Cell: Stochastic Resonance. J Phys Chem Lett 2014; 5:1012-1016. [PMID: 26270981 DOI: 10.1021/jz500152m] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Binding of a specific siRNA to the target mRNA in a live cell (human breast cancer cell, MCF-7) is studied by confocal microscopy. The specific siRNA (labeled with a fluorophore, alexa 488) exhibits much higher intensity of fluorescence in the bound state than in the free (unbound) state. It is observed that repeated unbinding and rebinding of siRNA (to target mRNA) occur before gene silencing. 16 273 on-time periods (residence or dwell time of siRNA in bound form) are detected. They follow a strikingly simple pattern. All of the on-time periods are odd-integral multiples of 5.5 ± 0.05 ms. This is ascribed to stochastic resonance.
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Affiliation(s)
- Shyamtanu Chattoraj
- †Department of Physical Chemistry and ‡Department of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
| | - Shekhar Saha
- †Department of Physical Chemistry and ‡Department of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
| | - Siddhartha Sankar Jana
- †Department of Physical Chemistry and ‡Department of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
| | - Kankan Bhattacharyya
- †Department of Physical Chemistry and ‡Department of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
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8
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Fluorescent protein-based biosensors and their clinical applications. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2014; 113:313-48. [PMID: 23244794 DOI: 10.1016/b978-0-12-386932-6.00008-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Green fluorescent protein and its relatives have shed their light on a wide range of biological problems. To date, with a color palette consisting of fluorescent proteins with different spectra, researchers can "paint" living cells as they desire. Moreover, sophisticated biosensors engineered to contain single or multiple fluorescent proteins, including FRET-based biosensors, spatiotemporally unveil molecular mechanisms underlying physiological processes. Although such molecules have contributed considerably to basic research, their abilities to be used in applied life sciences have yet to be fully explored. Here, we review the molecular bases of fluorescent proteins and fluorescent protein-based biosensors and focus on approaches aimed at applying such proteins to the clinic.
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Single Molecule Analysis Research Tool (SMART): an integrated approach for analyzing single molecule data. PLoS One 2012; 7:e30024. [PMID: 22363412 PMCID: PMC3282690 DOI: 10.1371/journal.pone.0030024] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2011] [Accepted: 12/12/2011] [Indexed: 11/19/2022] Open
Abstract
Single molecule studies have expanded rapidly over the past decade and have the ability to provide an unprecedented level of understanding of biological systems. A common challenge upon introduction of novel, data-rich approaches is the management, processing, and analysis of the complex data sets that are generated. We provide a standardized approach for analyzing these data in the freely available software package SMART: Single Molecule Analysis Research Tool. SMART provides a format for organizing and easily accessing single molecule data, a general hidden Markov modeling algorithm for fitting an array of possible models specified by the user, a standardized data structure and graphical user interfaces to streamline the analysis and visualization of data. This approach guides experimental design, facilitating acquisition of the maximal information from single molecule experiments. SMART also provides a standardized format to allow dissemination of single molecule data and transparency in the analysis of reported data.
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10
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Crivat G, Taraska JW. Imaging proteins inside cells with fluorescent tags. Trends Biotechnol 2011; 30:8-16. [PMID: 21924508 DOI: 10.1016/j.tibtech.2011.08.002] [Citation(s) in RCA: 189] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2011] [Revised: 08/04/2011] [Accepted: 08/04/2011] [Indexed: 11/30/2022]
Abstract
Watching biological molecules provides clues to their function and regulation. Some of the most powerful methods of labeling proteins for imaging use genetically encoded fluorescent fusion tags. There are four standard genetic methods of covalently tagging a protein with a fluorescent probe for cellular imaging. These use (i) autofluorescent proteins, (ii) self-labeling enzymes, (iii) enzymes that catalyze the attachment of a probe to a target sequence, and (iv) biarsenical dyes that target tetracysteine motifs. Each of these techniques has advantages and disadvantages. In this review, we cover new developments in these methods and discuss practical considerations for their use in imaging proteins inside living cells.
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Affiliation(s)
- Georgeta Crivat
- University of Maryland, College Park, Department of Entomology and Program in Cell and Molecular Biology, College Park, MD 20742, USA
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Marek MS, Johnson-Buck A, Walter NG. The shape-shifting quasispecies of RNA: one sequence, many functional folds. Phys Chem Chem Phys 2011; 13:11524-37. [PMID: 21603685 DOI: 10.1039/c1cp20576e] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
E Unus pluribum, or "Of One, Many", may be at the root of decoding the RNA sequence-structure-function relationship. RNAs embody the large majority of genes in higher eukaryotes and fold in a sequence-directed fashion into three-dimensional structures that perform functions conserved across all cellular life forms, ranging from regulating to executing gene expression. While it is the most important determinant of the RNA structure, the nucleotide sequence is generally not sufficient to specify a unique set of secondary and tertiary interactions due to the highly frustrated nature of RNA folding. This frustration results in folding heterogeneity, a common phenomenon wherein a chemically homogeneous population of RNA molecules folds into multiple stable structures. Often, these alternative conformations constitute misfolds, lacking the biological activity of the natively folded RNA. Intriguingly, a number of RNAs have recently been described as capable of adopting multiple distinct conformations that all perform, or contribute to, the same function. Characteristically, these conformations interconvert slowly on the experimental timescale, suggesting that they should be regarded as distinct native states. We discuss how rugged folding free energy landscapes give rise to multiple native states in the Tetrahymena Group I intron ribozyme, hairpin ribozyme, sarcin-ricin loop, ribosome, and an in vitro selected aptamer. We further describe the varying degrees to which folding heterogeneity impacts function in these RNAs, and compare and contrast this impact with that of heterogeneities found in protein folding. Embracing that one sequence can give rise to multiple native folds, we hypothesize that this phenomenon imparts adaptive advantages on any functionally evolving RNA quasispecies.
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Affiliation(s)
- Matthew S Marek
- Department of Chemistry, 930 N. University Ave., University of Michigan, Ann Arbor, MI 48109-1055, USA
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12
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Li Y, Qu X, Ma A, Smith GJ, Scherer NF, Dinner AR. Models of single-molecule experiments with periodic perturbations reveal hidden dynamics in RNA folding. J Phys Chem B 2009; 113:7579-90. [PMID: 19415919 DOI: 10.1021/jp900225q] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Traditionally, microscopic fluctuations of molecules have been probed by measuring responses of an ensemble to perturbations. Now, single-molecule experiments are capable of following fluctuations without introducing perturbations. However, dynamics not readily sampled at equilibrium should be accessible to nonequilibrium single-molecule measurements. In a recent study [Qu, X. et al. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 6602-6607], the efficiency of fluorescence resonance energy transfer (FRET) between probes on the L18 loop and 3' terminus of the 260 nucleotide RNase P RNA from Bacillus stearothermophilus was found to exhibit complex kinetics that depended on the (periodically alternating) concentration of magnesium ions ([Mg2+]) in solution. Specifically, this time series was found to exhibit a quasi-periodic response to a square-wave pattern of [Mg2+] changes. Because these experiments directly probe only one of the many degrees of freedom in the macromolecule, models are needed to interpret these data. We find that Hidden Markov Models are inadequate for describing the nonequilibrium dynamics, but they serve as starting points for the construction of models in which a discrete observable degree of freedom is coupled to a continuously evolving (hidden) variable. Consideration of several models of this general form indicates that the quasi-periodic response in the nonequilibrium experiments results from the switching (back and forth) in positions of the minima of the effective potential for the hidden variable. This switching drives oscillation of that variable and synchronizes the population to the changing [Mg2+]. We set the models in the context of earlier theoretical and experimental studies and conclude that single-molecule experiments with periodic peturbations can indeed yield qualitatively new information beyond that obtained at equilibrium.
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Affiliation(s)
- Ying Li
- Department of Physics, James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA
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Hsu STD, Blaser G, Jackson SE. The folding, stability and conformational dynamics of beta-barrel fluorescent proteins. Chem Soc Rev 2009; 38:2951-65. [PMID: 19771338 DOI: 10.1039/b908170b] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This critical review describes our current knowledge on the folding, stability and conformational dynamics of fluorescent proteins (FPs). The biophysical studies that have led to the elucidation of many of the key features of the complex energy landscape for folding for GFP and its variants are discussed. These illustrate some important issues surrounding how the large beta-barrel structure forms, and will be of interest to the protein folding community. In addition, the review highlights the importance of some of these results for the use of FPs in in vivo applications. The results should facilitate and aid in experimental designs of in vivo applications, as well as the interpretation of in vivo experimental data. The review is therefore of interest to all those working with FPs in vivo (103 references).
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Affiliation(s)
- Shang-Te Danny Hsu
- Chemistry Department, University of Cambridge, Lensfield Road, Cambridge, UK CB2 1EW
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14
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Wu D, Ghosh K, Inamdar M, Lee HJ, Fraser S, Dill K, Phillips R. Trajectory approach to two-state kinetics of single particles on sculpted energy landscapes. PHYSICAL REVIEW LETTERS 2009; 103:050603. [PMID: 19792475 PMCID: PMC3273425 DOI: 10.1103/physrevlett.103.050603] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2008] [Indexed: 05/17/2023]
Abstract
We study the trajectories of a single colloidal particle as it hops between two energy wells which are sculpted using optical traps. Whereas the dynamical behaviors of such systems are often treated by master-equation methods that focus on particles as actors, we analyze them instead using a trajectory-based variational method called maximum caliber (MaxCal). We show that the MaxCal strategy accurately predicts the full dynamics that we observe in the experiments: From the observed averages, it predicts second and third moments and covariances, with no free parameters. The covariances are the dynamical equivalents of Maxwell-like equilibrium reciprocal relations and Onsager-like dynamical relations.
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Affiliation(s)
- David Wu
- California Institute of Technology, Pasadena, California, USA
| | - Kingshuk Ghosh
- University of California, San Francisco, California, USA
| | | | - Heun Jin Lee
- California Institute of Technology, Pasadena, California, USA
| | - Scott Fraser
- California Institute of Technology, Pasadena, California, USA
| | - Ken Dill
- University of California, San Francisco, California, USA
| | - Rob Phillips
- California Institute of Technology, Pasadena, California, USA
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15
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George AA, Louis Schiltz R, Hager GL. Dynamic access of the glucocorticoid receptor to response elements in chromatin. Int J Biochem Cell Biol 2009; 41:214-24. [PMID: 18930837 PMCID: PMC2632576 DOI: 10.1016/j.biocel.2008.09.019] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2008] [Revised: 09/22/2008] [Accepted: 09/23/2008] [Indexed: 12/22/2022]
Abstract
Transcriptional activation as a rate-limiting step of gene expression is often triggered by an environmental stimulus that is transmitted through a signaling cascade to specific transcription factors. Transcription factors must then find appropriate target genes in the context of chromatin. Subsequent modulation of local chromatin domains is now recognized as a major mechanism of gene regulation. The interactions of transcription factors with chromatin structures have recently been observed to be highly dynamic, with residence times measured in seconds. Thus, the concept of static, multi-protein complexes forming at regulatory elements in the genome has been replaced by a new paradigm that envisages rapid and continuous exchange events with the template. These highly dynamic interactions are a property of both DNA-protein and protein-protein interactions and are inherent to every stage of the transcriptional response. In this review we discuss the dynamics of a nuclear receptor, and its transcriptional response in the chromatin context.
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Affiliation(s)
- Anuja A. George
- Laboratory of Receptor Biology and Gene Expression, Building 41, B602, 41 Library Dr., National Cancer Institute, NIH, Bethesda, MD 20892-5055
| | - R. Louis Schiltz
- Laboratory of Receptor Biology and Gene Expression, Building 41, B602, 41 Library Dr., National Cancer Institute, NIH, Bethesda, MD 20892-5055
| | - Gordon L. Hager
- Laboratory of Receptor Biology and Gene Expression, Building 41, B602, 41 Library Dr., National Cancer Institute, NIH, Bethesda, MD 20892-5055
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16
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Bosisio C, Quercioli V, Collini M, D'Alfonso L, Baldini G, Bettati S, Campanini B, Raboni S, Chirico G. Protonation and conformational dynamics of GFP mutants by two-photon excitation fluorescence correlation spectroscopy. J Phys Chem B 2008; 112:8806-14. [PMID: 18582099 DOI: 10.1021/jp801164n] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
GFP mutants are known to display fluorescence flickering, a process that occurs in a wide time range. Because serine 65, threonine 203, glutamate 222, and histidine 148 have been indicated as key residues in determining the GFP fluorescence photodynamics, we have focused here on the role of histidine 148 and glutamate 222 by studying the fluorescence dynamics of GFPmut2 (S65A, V68L, and S72A GFP) and its H148G (Mut2G) and E222Q (Mut2Q) mutants. Two relaxation components are found in the fluorescence autocorrelation functions of GFPmut2: a 10-100 micros pH-dependent component and a 100-500 micros laser-power-dependent component. The comparison of these three mutants shows that the mutation of histidine 148 to glycine induces a 3-fold increase in the protonation rate, thereby indicating that the protonation-deprotonation of the chromophore occurs via a proton exchange with the solution mediated by the histidine 148 residue. The power-dependent but pH-independent relaxation mode, which is not affected by the E222Q and H148G mutations, is due to an excited-state process that is probably related to conformational rearrangements of the chromophore after the photoexcitation, more than to the chromophore excited-state proton transfer.
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Affiliation(s)
- C Bosisio
- Dipartimento G. Occhialini, Universita di Milano Bicocca
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17
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Sinha KK, Udgaonkar JB. Barrierless evolution of structure during the submillisecond refolding reaction of a small protein. Proc Natl Acad Sci U S A 2008; 105:7998-8003. [PMID: 18523007 PMCID: PMC2430349 DOI: 10.1073/pnas.0803193105] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2008] [Indexed: 11/18/2022] Open
Abstract
To determine whether a protein folding reaction can occur in the absence of a dominant barrier is crucial for understanding its complexity. Here direct ultrafast kinetic measurements have been used to study the initial submillisecond (sub-ms) folding reaction of the small protein barstar. The cooperativity of the initial folding reaction has been explored by using two probes: fluorescence resonance energy transfer, through which the contraction of two intramolecular distances is measured, and the binding of 8-anilino-1-naphthalene sulfonic acid, through which the formation of hydrophobic clusters is monitored. A fast chain contraction is shown to precede the formation of hydrophobic clusters, indicating that the sub-ms folding reaction is not cooperative. The observed rate constant of the sub-ms folding reaction monitored by 8-anilino-1-naphthalene sulfonic acid fluorescence has been found to be the same in stabilizing conditions (low urea concentrations), in which specific structure is formed, and in marginally stabilizing conditions (higher urea concentrations), where virtually no structure is formed in the product of the sub-ms folding reaction. The observation that the folding rate is independent of the folding conditions suggests that the initial folding reaction occurs in the absence of a dominant free energy barrier. These results provide kinetic evidence that the formation of specific structure need not be slowed down by any significant free energy barrier during the course of a very fast protein folding reaction.
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Affiliation(s)
- Kalyan K. Sinha
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Jayant B. Udgaonkar
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
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18
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Affiliation(s)
- Alessandro Borgia
- Department of Chemistry, Cambridge University, Medical Research Council Centre for Protein Engineering, Cambridge, CB2 1EW, United Kingdom; ,
| | - Philip M. Williams
- Laboratory of Biophysics and Surface Analysis, School of Pharmacy, University of Nottingham, Nottingham NG7 2RD, United Kingdom;
| | - Jane Clarke
- Department of Chemistry, Cambridge University, Medical Research Council Centre for Protein Engineering, Cambridge, CB2 1EW, United Kingdom; ,
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19
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Orte A, Craggs TD, White SS, Jackson SE, Klenerman D. Evidence of an Intermediate and Parallel Pathways in Protein Unfolding from Single-Molecule Fluorescence. J Am Chem Soc 2008; 130:7898-907. [DOI: 10.1021/ja709973m] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Angel Orte
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Timothy D. Craggs
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Samuel S. White
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - Sophie E. Jackson
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | - David Klenerman
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
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20
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Prakash MK, Marcus RA. Dielectric dispersion interpretation of single enzyme dynamic disorder, spectral diffusion, and radiative fluorescence lifetime. J Phys Chem B 2007; 112:399-404. [PMID: 17956086 DOI: 10.1021/jp0758869] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A formulation based on measurable dielectric dispersion of enzymes is developed to estimate fluctuations in electrostatic interaction energy on time scales as long as milliseconds to seconds at a local site in enzymes. Several single molecule experimental obsevations occur on this time scale, currently unreachable by real time computational trajectory simulations. We compare the experimental results on the autocorrelation function of the fluctuations of catalysis rate with the calculations using the dielectric dispersion formulation. We also discuss the autocorrelation functions of the fluorescence lifetime and of spectral diffusion. We use a previously derived relation between the observables and the electric field fluctuations and calculate the latter using dielectric dispersion data for the proteins and the Onsager regression hypothesis.
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Affiliation(s)
- Meher K Prakash
- Noyes Laboratory of Chemical Physics MC 127-72, California Institute of Technology, Pasadena, CA 91125, USA
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21
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Prakash MK, Marcus RA. An interpretation of fluctuations in enzyme catalysis rate, spectral diffusion, and radiative component of lifetimes in terms of electric field fluctuations. Proc Natl Acad Sci U S A 2007; 104:15982-7. [PMID: 17911244 PMCID: PMC2042148 DOI: 10.1073/pnas.0707859104] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Time-dependent fluctuations in the catalysis rate (deltak(t)) observed in single-enzyme experiments were found in a particular study to have an autocorrelation function decaying on the same time scale as that of spectral diffusion deltaomega(0)(t). To interpret this similarity, the present analysis focuses on a factor in enzyme catalysis, the local electrostatic interaction energy (E) at the active site and its effect on the activation free energy barrier. We consider the slow fluctuations of the electrostatic interaction energy (deltaE(t)) as a contributor to deltak(t) and relate the latter to deltaomega(0)(t). The resulting relation between deltak(t) and deltaomega(0)(t) is a dynamic analog of the solvatochromism used in interpreting solvent effects on organic reaction rates. The effect of the postulated deltaE(t) on fluctuations in the radiative component (deltagamma(r)(-1)(t)) of the fluorescence decay of chromophores in proteins also is examined, and a relation between deltagamma(r)(-1)(t) and deltaomega(0)(t) is obtained. Experimental tests will determine whether the correlation functions for deltak(t), deltaomega(0)(t), and deltagamma(r)(-1) are indeed similar for any enzyme. Measurements of dielectric dispersion, epsilon(omega), for the enzyme discussed elsewhere will provide further insight into the correlation function for deltaE(t). They also will determine whether fluctuations in the nonradiative component gamma(nr)(-1) of the lifetime decay has a different origin, fluctuations in distance for example.
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Affiliation(s)
- Meher K. Prakash
- Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125
| | - R. A. Marcus
- Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125
- *To whom correspondence should be addressed at:
Arthur Amos Noyes Professor of Chemistry, Noyes Laboratory of Chemical Physics, California Institute of Technology, 1200 East California Boulevard, MC 127-72, Pasadena, CA 91125. E-mail:
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22
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Delgado-Buscalioni R, De Fabritiis G. Embedding molecular dynamics within fluctuating hydrodynamics in multiscale simulations of liquids. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2007; 76:036709. [PMID: 17930363 DOI: 10.1103/physreve.76.036709] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2007] [Indexed: 05/25/2023]
Abstract
We present a hybrid protocol designed to couple the dynamics of a nanoscopic region of liquid described at atomistic level with a fluctuating hydrodynamics description of the surrounding liquid. The hybrid technique is based on the exchange of fluxes and it is shown to respect the conservation laws of fluid mechanics. This fact allows us to solve unsteady flows involving shear and sound waves crossing the interface of both domains. In equilibrium we find perfect agreement with the grand-canonical ensemble at low and moderate densities, while within the nanoscopic volumes considered, mass fluctuation (both in hybrid and full MD simulations) becomes slightly larger than predicted by the thermodynamic limit. Stress fluctuations across the hybrid interface are shown to have a seamless profile. Nonequilibrium scenarios involving shear (startup of Couette flow) and longitudinal flow (sound waves) are also illustrated.
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Affiliation(s)
- R Delgado-Buscalioni
- Departamento de Física Teorica de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, Madrid E-28049, Spain.
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23
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Abstract
Keeping protein molecules in the active state on a solid surface is essential to protein microarrays and other protein-based biosensors. Here, we show that the 2-D chemical environment controls the refolding of the denatured green fluorescent proteins tethered to solid surfaces. Refolding occurs readily on the repulsive PEG functionalized surface but is inhibited on the attractive--NH(2) functionalized surface. This result shows the critical importance of the 2-D chemical environment in the maintenance and revival of protein activity on surfaces and opens the door to designing 2-D molecular chaperones for protein folding.
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24
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Cannone F, Collini M, Chirico G, Baldini G, Bettati S, Campanini B, Mozzarelli A. Environment effects on the oscillatory unfolding kinetics of GFP. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2007; 36:795-803. [PMID: 17429619 DOI: 10.1007/s00249-007-0160-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2006] [Revised: 03/13/2007] [Accepted: 03/20/2007] [Indexed: 11/29/2022]
Abstract
The chromophore of a green fluorescent protein (GFP) mutant engineered to enhance emission and stability is known to display erratic switchings among a few of its chemical substates and, in particular, between the anionic A and the neutral N substates, whose difference is associated with a proton exchange and a consequent conformation rearrangement. However, when close to unfolding, the A-N switchings suddenly become very regular as shown by fluorescence oscillations that have been recently observed for molecules embedded in wet silica gel. In order to establish whether the matrix hosting the protein is responsible for these oscillations, we investigated the effect of another medium (silanized surfaces), of a different denaturant (urea) and of cosolvents (D(2)O and glycerol). The occurrence of periodic A-N switchings, in the last milliseconds before GFP unfolding, is observed under all investigated conditions, together with three specific frequency values that characterize the pre-unfolding fluorescence. Urea and guanidinium, the denaturants employed in order to unfold GFP, do not lead to appreciable differences in the observed switching parameters, whereas the different media embedding the protein give rise only to frequency shifts that scale with the viscosity of the host. The periodicity of the GFP A-N switchings and their dependence on cosolvents suggest that they could be associated with oscillatory motions between meta-stable conformations of the beta-barrel surrounding the chromophore near protein unfolding.
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Affiliation(s)
- Fabio Cannone
- Department of Physics, University of Milano-Bicocca, Milan, Italy
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25
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26
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Cannone F, Milani R, Chirico G, Diaspro A, Krol S, Campanini B. Voltage regulation of single green fluorescent protein mutants. Biophys Chem 2007; 125:368-74. [PMID: 17059862 DOI: 10.1016/j.bpc.2006.09.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2006] [Revised: 09/25/2006] [Accepted: 09/25/2006] [Indexed: 11/18/2022]
Abstract
We report the analysis of the fluorescence intensity fluctuations of single proteins of a GFP mutant, GFPmut2, embedded in a polyelectrolyte nanocapsule adsorbed on thin conductive layers. Our results, based on single molecule fluorescence spectroscopy, indicate that the fluorescence blinking dynamics of GFP is strongly dependent on the bulk conductivity of the metal layer substrate, on the distance from the conductive surfaces and on the amplitude of the voltage applied to the poly-electrolyte layers. These findings suggest that fluorescence blinking itself might be employed as a reporter signal in nano-bio-technology applications.
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Affiliation(s)
- Fabio Cannone
- Department of Physics, LABS, University of Milano Bicocca, Piazza della scienza 3, 20126 Milano, Italy
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27
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Pontiggia F, Colombo G, Micheletti C, Orland H. Anharmonicity and self-similarity of the free energy landscape of protein G. PHYSICAL REVIEW LETTERS 2007; 98:048102. [PMID: 17358816 DOI: 10.1103/physrevlett.98.048102] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2006] [Indexed: 05/14/2023]
Abstract
The near-native free-energy landscape of protein G is investigated through 0.4-micros-long atomistic molecular dynamics simulations in an explicit solvent. A theoretical and computational framework is used to assess the time dependence of salient thermodynamical features. While the quasiharmonic character of the free energy is found to degrade in a few ns, the slow modes display a very mild dependence on the trajectory duration. This property originates from a striking self-similarity of the free-energy landscape embodied by the consistency of the principal directions of the local minima, where the system dwells for several ns, and of the virtual jumps connecting them.
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Affiliation(s)
- F Pontiggia
- International School for Advanced Studies and CNR-INFM Democritos, Via Beirut 2-4, 34014 Trieste, Italy
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28
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Rocha VA, Eggers DK. Hydrophobic, organically-modified silica gels enhance the secondary structure of encapsulated apomyoglobin. Chem Commun (Camb) 2007:1266-8. [PMID: 17356778 DOI: 10.1039/b617078a] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Insertion of hydrophobic groups in a silica matrix, by addition of propyl- or trifluoropropyltrimethoxysilane, leads to a surprising increase in the helical content of apomyoglobin following encapsulation by the sol-gel technique.
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Affiliation(s)
- Veronica A Rocha
- Department of Chemistry, San José State University, San José, CA 95192-0101, USA
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29
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Baldini G, Cannone F, Chirico G, Collini M, Campanini B, Bettati S, Mozzarelli A. Evidence of discrete substates and unfolding pathways in green fluorescent protein. Biophys J 2006; 92:1724-31. [PMID: 17142282 PMCID: PMC1796838 DOI: 10.1529/biophysj.106.093567] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We present evidence of conformational substates of a green fluorescent protein mutant, GFPmut2, and of their relationship with the protein behavior during chemical unfolding. The fluorescence of single molecules, excited by two infrared photons from a pulsed laser, was detected in two separate channels that simultaneously collected the blue or the green emission from the protein chromophore chemical states (anionic or neutral, respectively). Time recording of the fluorescence signals from molecules in the native state shows that the chromophore, an intrinsic probe sensitive to conformational changes, switches between the two states with average rates that are found to assume distinct values, thereby suggesting a multiplicity of protein substates. Furthermore, under denaturing conditions, the chromophore switching rate displays different and reproducible time evolutions that are characterized by discrete unfolding times. The correlation that is found between native molecules' switching rate values and unfolding times appears as direct evidence that GFPmut2 can unfold only along distinct paths that are determined by the initial folded substate of the protein.
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30
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Liu Y, Kim HR, Heikal AA. Structural basis of fluorescence fluctuation dynamics of green fluorescent proteins in acidic environments. J Phys Chem B 2006; 110:24138-46. [PMID: 17125385 PMCID: PMC2556077 DOI: 10.1021/jp062164t] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Green fluorescent proteins (GFPs) have become powerful markers for numerous biological studies due to their robust fluorescence properties, site-specific labeling, pH sensitivity, and mutations for multiple-site labeling. Fluorescence correlation spectroscopy (FCS) studies have indicated that fluorescence blinking of anionic GFP mutants takes place on a time scale of 45-300 ms, depending on pH, and have been attributed to external proton transfer. Here we present experimental evidence indicating that conformational change in the protein &beta-barrel is a determining step for the external protonation of GFP-S65T (at low pH) using time-resolved fluorescence and polarization anisotropy measurements. While the average anionic fluorescence lifetime of GFP-S65T is reduced by approximately 18% over a pH range of 3.6-10.0, the fluorescence polarization anisotropy decays mostly as a single exponential with a rotational time of phi = 17 +/- 1 ns, which indicates an intact beta-barrel with a hydrodynamic volume of 78 +/- 5 nm3. In contrast, the total fluorescence (525 +/- 50 nm) of the excited neutral state of S65T reveals a strong correlation between the fluorescence lifetime, structural conformation, and pH. The average fluorescence lifetime of the excited neutral state of S65T as a function of pH yields pKa approximately 5.9 in agreement with literature values using steady-state techniques. In contrast to the intact beta-barrel at high pH, the anisotropy of neutral S65T (at pH
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Affiliation(s)
- Yuexin Liu
- Department of Bioengineering, The Pennsylvania State University, University Park, PA 16802
| | - Hye-Ryong Kim
- Department of Bioengineering, The Pennsylvania State University, University Park, PA 16802
| | - Ahmed A. Heikal
- Department of Bioengineering, The Pennsylvania State University, University Park, PA 16802
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31
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De Fabritiis G, Delgado-Buscalioni R, Coveney PV. Multiscale modeling of liquids with molecular specificity. PHYSICAL REVIEW LETTERS 2006; 97:134501. [PMID: 17026036 DOI: 10.1103/physrevlett.97.134501] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2006] [Indexed: 05/04/2023]
Abstract
The separation between molecular and mesoscopic length and time scales poses a severe limit to molecular simulations of mesoscale phenomena. We describe a hybrid multiscale computational technique which addresses this problem by keeping the full molecular nature of the system where it is of interest and coarse graining it elsewhere. This is made possible by coupling molecular dynamics with a mesoscopic description of realistic liquids based on Landau's fluctuating hydrodynamics. We show that our scheme correctly couples hydrodynamics and that fluctuations, at both the molecular and continuum levels, are thermodynamically consistent. Hybrid simulations of sound waves in bulk water and reflected by a lipid monolayer are presented as illustrations of the scheme.
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Affiliation(s)
- G De Fabritiis
- Centre for Computational Science, Department of Chemistry, University College London, 20 Gordon Street, WC1H 0AJ London, United Kingdom.
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32
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Cannone F, Chirico G, Bizzarri AR, Cannistraro S. Quenching and Blinking of Fluorescence of a Single Dye Molecule Bound to Gold Nanoparticles. J Phys Chem B 2006; 110:16491-8. [PMID: 16913781 DOI: 10.1021/jp0625816] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A fluorescein derivative (SAMSA) bound to gold nanoparticles of different diameters is investigated by time-resolved fluorescence at the single molecule level in a wide dynamic range, from nanosecond to second time scale. The significant decrease of both SAMSA excited state lifetime and fluorescence quantum yield observed upon binding to gold nanoparticles can be essentially traced back to an increase of the nonradiative deactivation rate, probably due to energy transfer, that depends on the nanoparticle size. A slow single molecule fluorescence blinking, in the ms time scale, has a marked dependence on the excitation intensity both under single and under two photon excitation. The blinking dynamics is limited by a low probability nonlinear excitation to a high energy state from which a transition to a dark state occurs. The results point out a strong coupling between the vibro-electronic configuration of the dye and the plasmonic features of the metal nanoparticles that provide dye radiationless deactivation channels on a wide dynamic range.
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Affiliation(s)
- Fabio Cannone
- Laboratory for Advanced BioSpectroscopy (LABS), INFM-CNR, Physics Department, University of Milano-Bicocca, Milano I-20126, Italy
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33
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Chirico G, Cannone F, Diaspro A. Unfolding time distribution of GFP by single molecule fluorescence spectroscopy. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2006; 35:663-74. [PMID: 16786346 DOI: 10.1007/s00249-006-0075-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2006] [Revised: 05/05/2006] [Accepted: 05/18/2006] [Indexed: 11/27/2022]
Abstract
We have studied the unfolding of single molecules of GFP-mut2 mutant trapped in wet silica gels in a wide range of GuHCl concentration. After the addition of denaturant, the number of fluorescent molecules decreases with unfolding rates (of the order of 0.01 min(-1)) that are in very good agreement with bulk fluorescence and circular dichroism data. Unexpectedly, single molecule experiments show rare fluctuations in the number of fluorescent proteins at equilibrium. On the other hand, although a first approximate description of the number decays can be reasonably performed by single exponential functions, the distributions of the single molecule unfolding times show a maximum at times congruent with 50-100 min up to the denaturation midpoint concentration of [GuHCl] congruent with 2.5 M. A theoretical analysis of the distributions indicates that this feature is a fingerprint of the competition between unfolding and refolding processes when the protein is very far from the midpoint denaturant concentration.
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Affiliation(s)
- G Chirico
- Department of Physics, University of Milano Bicocca, Piazza della Scienza 3, Milano, Italy.
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34
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Hager GL, Elbi C, Johnson TA, Voss T, Nagaich AK, Schiltz RL, Qiu Y, John S. Chromatin dynamics and the evolution of alternate promoter states. Chromosome Res 2006; 14:107-16. [PMID: 16506100 DOI: 10.1007/s10577-006-1030-0] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Eucaryotic gene transcriptional switches utilize changes both in the activity and composition of soluble transcription factor complexes, and epigenetic modifications to the chromatin template. Until recently, alternate states of promoter activity have been associated with the assembly of relatively stable multiprotein complexes on target genes, with transitions in the composition of these complexes occurring on the time scale of minutes or hours. The development of living cell techniques to characterize transcription factor function in real time has led to an alternate view of highly dynamic protein/template interactions. In addition, emerging evidence suggests that energy-dependent processes contribute significantly to the rapid movement of proteins in living cells, and to the exchange of sequence-specific DNA-binding proteins with regulatory elements. Potential mechanisms involved in the unexpectedly rapid flux of factor/template interactions are discussed in the context of a "return-to-template" model for transcription factor function.
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Affiliation(s)
- Gordon L Hager
- Laboratory of Receptor Biology and Gene Expression, Center for Cancer Research, National Cancer Institute, NIH, Building 41, Room B602, Bethesda, MD 20892-5055, USA.
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35
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Delgado-Buscalioni R. Cyclic motion of a grafted polymer under shear flow. PHYSICAL REVIEW LETTERS 2006; 96:088303. [PMID: 16606232 DOI: 10.1103/physrevlett.96.088303] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2005] [Indexed: 05/08/2023]
Abstract
The long-time dynamics of a single end-tethered chain under shear flow are studied using molecular and Brownian dynamics simulations of a flexible polymer. As observed in previous experiments with tethered DNA [Phys. Rev. Lett. 84, 4769 (2000)], under a flow sheared at constant rate the chain performs a cyclic motion. But, contrary to what has been previously suggested, a well-defined characteristic period exists and it is clearly revealed in the cross spectra of the chain extension along flow and gradient directions. The main cycling time scales like the time needed to stretch the polymer by convection, being about 10 times the relaxation time of the chain in flow. This coherent recursive motion introduces long memory in the fluid and suggests resonance effects under periodic external forcing.
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Affiliation(s)
- Rafael Delgado-Buscalioni
- Departamento de Ciencias y Técnicas Fisicoquímicas, Universidad de Educación a Distancia, C/Senda del Rey, 9, Madrid 28040, Spain.
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