1
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The road less traveled in protein folding: evidence for multiple pathways. Curr Opin Struct Biol 2020; 66:83-88. [PMID: 33220553 DOI: 10.1016/j.sbi.2020.10.012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Accepted: 10/11/2020] [Indexed: 11/23/2022]
Abstract
Free Energy Landscape theory of Protein Folding, introduced over 20 years ago, implies that a protein has many paths to the folded conformation with the lowest free energy. Despite the knowledge in principle, it has been remarkably hard to detect such pathways. The lack of such observations is primarily due to the fact that no one experimental technique can detect many parts of the protein simultaneously with the time resolution necessary to see such differences in paths. However, recent technical developments and employment of multiple experimental probes and folding prompts have illuminated multiple folding pathways in a number of proteins that had all previously been described with a single path.
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2
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Exploring the Denatured State Ensemble by Single-Molecule Chemo-Mechanical Unfolding: The Effect of Force, Temperature, and Urea. J Mol Biol 2017; 430:450-464. [PMID: 28782558 DOI: 10.1016/j.jmb.2017.07.022] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Revised: 07/29/2017] [Accepted: 07/31/2017] [Indexed: 11/22/2022]
Abstract
While it is widely appreciated that the denatured state of a protein is a heterogeneous conformational ensemble, there is still debate over how this ensemble changes with environmental conditions. Here, we use single-molecule chemo-mechanical unfolding, which combines force and urea using the optical tweezers, together with traditional protein unfolding studies to explore how perturbants commonly used to unfold proteins (urea, force, and temperature) affect the denatured-state ensemble. We compare the urea m-values, which report on the change in solvent accessible surface area for unfolding, to probe the denatured state as a function of force, temperature, and urea. We find that while the urea- and force-induced denatured states expose similar amounts of surface area, the denatured state at high temperature and low urea concentration is more compact. To disentangle these two effects, we use destabilizing mutations that shift the Tm and Cm. We find that the compaction of the denatured state is related to changing temperature as the different variants of acyl-coenzyme A binding protein have similar m-values when they are at the same temperature but different urea concentration. These results have important implications for protein folding and stability under different environmental conditions.
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3
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Abstract
Prion diseases, like Alzheimer's disease and Parkinson disease, are rapidly progressive neurodegenerative disorders caused by misfolding followed by aggregation and accumulation of protein deposits in neuronal cells. Here we measure intramolecular polypeptide backbone reconfiguration as a way to understand the molecular basis of prion aggregation. Our hypothesis is that when reconfiguration is either much faster or much slower than bimolecular diffusion, biomolecular association is not stable, but as the reconfiguration rate becomes similar to the rate of biomolecular diffusion, the association is more stable and subsequent aggregation is faster. Using the technique of Trp-Cys contact quenching, we investigate the effects of various conditions on reconfiguration dynamics of the Syrian hamster and rabbit prion proteins. This protein exhibits behavior in all three reconfiguration regimes. We conclude that the hamster prion is prone to aggregation at pH 4.4 because its reconfiguration rate is slow enough to expose hydrophobic residues on the same time scale that bimolecular association occurs, whereas the rabbit sequence avoids aggregation by reconfiguring 10 times faster than the hamster sequence.
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4
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Pirchi M, Tsukanov R, Khamis R, Tomov TE, Berger Y, Khara DC, Volkov H, Haran G, Nir E. Photon-by-Photon Hidden Markov Model Analysis for Microsecond Single-Molecule FRET Kinetics. J Phys Chem B 2016; 120:13065-13075. [PMID: 27977207 DOI: 10.1021/acs.jpcb.6b10726] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The function of biological macromolecules involves large-scale conformational dynamics spanning multiple time scales, from microseconds to seconds. Such conformational motions, which may involve whole domains or subunits of a protein, play a key role in allosteric regulation. There is an urgent need for experimental methods to probe the fastest of these motions. Single-molecule fluorescence experiments can in principle be used for observing such dynamics, but there is a lack of analysis methods that can extract the maximum amount of information from the data, down to the microsecond time scale. To address this issue, we introduce H2MM, a maximum likelihood estimation algorithm for photon-by-photon analysis of single-molecule fluorescence resonance energy transfer (FRET) experiments. H2MM is based on analytical estimators for model parameters, derived using the Baum-Welch algorithm. An efficient and effective method for the calculation of these estimators is introduced. H2MM is shown to accurately retrieve the reaction times from ∼1 s to ∼10 μs and even faster when applied to simulations of freely diffusing molecules. We further apply this algorithm to single-molecule FRET data collected from Holliday junction molecules and show that at low magnesium concentrations their kinetics are as fast as ∼104 s-1. The new algorithm is particularly suitable for experiments on freely diffusing individual molecules and is readily incorporated into existing analysis packages. It paves the way for the broad application of single-molecule fluorescence to study ultrafast functional dynamics of biomolecules.
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Affiliation(s)
- Menahem Pirchi
- Department of Chemical Physics, Weizmann Institute of Science , Rehovot 76100, Israel
| | - Roman Tsukanov
- Department of Chemistry and the Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev , Beer Sheva 84105, Israel
| | - Rashid Khamis
- Department of Chemical Physics, Weizmann Institute of Science , Rehovot 76100, Israel
| | - Toma E Tomov
- Department of Chemistry and the Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev , Beer Sheva 84105, Israel
| | - Yaron Berger
- Department of Chemistry and the Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev , Beer Sheva 84105, Israel
| | - Dinesh C Khara
- Department of Chemistry and the Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev , Beer Sheva 84105, Israel
| | - Hadas Volkov
- Department of Chemistry and the Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev , Beer Sheva 84105, Israel
| | - Gilad Haran
- Department of Chemical Physics, Weizmann Institute of Science , Rehovot 76100, Israel
| | - Eyal Nir
- Department of Chemistry and the Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev , Beer Sheva 84105, Israel
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5
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Basak S, Prasad GVRK, Varkey J, Chattopadhyay K. Early sodium dodecyl sulfate induced collapse of α-synuclein correlates with its amyloid formation. ACS Chem Neurosci 2015; 6:239-46. [PMID: 25369246 DOI: 10.1021/cn500168x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The aggregation of α-synuclein (A-syn) has been implicated strongly in Parkinson's disease (PD). In vitro studies established A-syn to be a member of the intrinsically disordered protein (IDP) family. This protein undergoes structural interconversion between an extended and a compact state, and this equilibrium influences the mechanism of its aggregation. A combination of fluorescence resonance energy transfer (FRET) and fluorescence correlation spectroscopy (FCS) has been used to study the membrane induced conformational reorganization and aggregation of A-syn. Different structural and conformational events, including the early collapse, the formation of the secondary structure, and aggregation have been identified and characterized using FCS and other biophysical methods. In addition, the concentrations of glycerol and urea have been varied to study the effect of solution conditions on the above conformational events. Further, we have extended this study on a number of A-syn mutants, namely, A30P, A53T, and E46K. These mutants are chosen because of their known implications in the disease pathology. The variation of solution conditions and mutational analyses suggest a strong correlation between the extent of early collapse and the onset of aggregation in PD.
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Affiliation(s)
- Sujit Basak
- Protein
Folding and Dynamics Laboratory Structural Biology and Bioinformatics
Division CSIR-Indian Institute of Chemical Biology (IICB) 4, Raja
S.C. Mullick Road, Kolkata-700032, India
| | - G. V. R Krishna Prasad
- Department
of Biological Sciences, Indian Institute of Science Education and Research, Sec 81, SAS Nagar, Mohali, Punjab-140306, India
| | - Jobin Varkey
- Centre
for Converging Technologies, University of Rajasthan, Jaipur-3002004, India
| | - Krishnananda Chattopadhyay
- Protein
Folding and Dynamics Laboratory Structural Biology and Bioinformatics
Division CSIR-Indian Institute of Chemical Biology (IICB) 4, Raja
S.C. Mullick Road, Kolkata-700032, India
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6
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Huang JT, Wang T, Huang SR, Li X. Reduced alphabet for protein folding prediction. Proteins 2015; 83:631-9. [PMID: 25641420 DOI: 10.1002/prot.24762] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Revised: 11/07/2014] [Accepted: 12/21/2014] [Indexed: 01/17/2023]
Abstract
What are the key building blocks that would have been needed to construct complex protein folds? This is an important issue for understanding protein folding mechanism and guiding de novo protein design. Twenty naturally occurring amino acids and eight secondary structures consist of a 28-letter alphabet to determine folding kinetics and mechanism. Here we predict folding kinetic rates of proteins from many reduced alphabets. We find that a reduced alphabet of 10 letters achieves good correlation with folding rates, close to the one achieved by full 28-letter alphabet. Many other reduced alphabets are not significantly correlated to folding rates. The finding suggests that not all amino acids and secondary structures are equally important for protein folding. The foldable sequence of a protein could be designed using at least 10 folding units, which can either promote or inhibit protein folding. Reducing alphabet cardinality without losing key folding kinetic information opens the door to potentially faster machine learning and data mining applications in protein structure prediction, sequence alignment and protein design.
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Affiliation(s)
- Jitao T Huang
- Department of Chemistry and National Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin, 300071, People's Republic of China
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7
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Volk M, Milanesi L, Waltho JP, Hunter CA, Beddard GS. The roughness of the protein energy landscape results in anomalous diffusion of the polypeptide backbone. Phys Chem Chem Phys 2015; 17:762-82. [DOI: 10.1039/c4cp03058c] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Recombination of photolysed protein disulfide bonds confirms subdiffusional backbone motion and measures the roughness of the protein's energy landscape.
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Affiliation(s)
- Martin Volk
- Department of Chemistry
- University of Liverpool
- Liverpool
- UK
| | - Lilia Milanesi
- School of Chemical and Biological Sciences
- Queen Mary
- University of London
- London
- UK
| | - Jonathan P. Waltho
- Department of Molecular Biology and Biotechnology
- University of Sheffield
- Sheffield
- UK
- Manchester Institute of Biotechnology
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8
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Chakraborty D, Collepardo-Guevara R, Wales DJ. Energy Landscapes, Folding Mechanisms, and Kinetics of RNA Tetraloop Hairpins. J Am Chem Soc 2014; 136:18052-61. [DOI: 10.1021/ja5100756] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Debayan Chakraborty
- Department
of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
| | | | - David J. Wales
- Department
of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
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9
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10
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Yasin UM, Sashi P, Bhuyan AK. Free Energy Landscape of Lysozyme: Multiple Near-Native Conformational States and Rollover in the Urea Dependence of Folding Energy. J Phys Chem B 2014; 118:6662-9. [DOI: 10.1021/jp501879s] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- U. Mahammad Yasin
- School of Chemistry, University of Hyderabad, Hyderabad 500 046, India
| | - Pulikallu Sashi
- School of Chemistry, University of Hyderabad, Hyderabad 500 046, India
| | - Abani K. Bhuyan
- School of Chemistry, University of Hyderabad, Hyderabad 500 046, India
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11
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Lyle N, Das RK, Pappu RV. A quantitative measure for protein conformational heterogeneity. J Chem Phys 2014; 139:121907. [PMID: 24089719 DOI: 10.1063/1.4812791] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Conformational heterogeneity is a defining characteristic of proteins. Intrinsically disordered proteins (IDPs) and denatured state ensembles are extreme manifestations of this heterogeneity. Inferences regarding globule versus coil formation can be drawn from analysis of polymeric properties such as average size, shape, and density fluctuations. Here we introduce a new parameter to quantify the degree of conformational heterogeneity within an ensemble to complement polymeric descriptors. The design of this parameter is guided by the need to distinguish between systems that couple their unfolding-folding transitions with coil-to-globule transitions and those systems that undergo coil-to-globule transitions with no evidence of acquiring a homogeneous ensemble of conformations upon collapse. The approach is as follows: Each conformation in an ensemble is converted into a conformational vector where the elements are inter-residue distances. Similarity between pairs of conformations is quantified using the projection between the corresponding conformational vectors. An ensemble of conformations yields a distribution of pairwise projections, which is converted into a distribution of pairwise conformational dissimilarities. The first moment of this dissimilarity distribution is normalized against the first moment of the distribution obtained by comparing conformations from the ensemble of interest to conformations drawn from a Flory random coil model. The latter sets an upper bound on conformational heterogeneity thus ensuring that the proposed measure for intra-ensemble heterogeneity is properly calibrated and can be used to compare ensembles for different sequences and across different temperatures. The new measure of conformational heterogeneity will be useful in quantitative studies of coupled folding and binding of IDPs and in de novo sequence design efforts that are geared toward controlling the degree of heterogeneity in unbound forms of IDPs.
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Affiliation(s)
- Nicholas Lyle
- Computational and Systems Biology Program, Division of Biology and Biomedical Sciences, Washington University in St. Louis, One Brookings Drive, Campus Box 1097, St. Louis, Missouri 63130, USA
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12
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Fazelinia H, Xu M, Cheng H, Roder H. Ultrafast hydrogen exchange reveals specific structural events during the initial stages of folding of cytochrome c. J Am Chem Soc 2013; 136:733-40. [PMID: 24364692 DOI: 10.1021/ja410437d] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Many proteins undergo a sharp decrease in chain dimensions during early stages of folding, prior to the rate-limiting step in folding. However, it remains unclear whether compact states are the result of specific folding events or a general hydrophobic collapse of the poly peptide chain driven by the change in solvent conditions. To address this fundamental question, we extended the temporal resolution of NMR-detected H/D exchange labeling experiments into the microsecond regime by adopting a microfluidics approach. By observing the competition between H/D exchange and folding as a function of labeling pH, coupled with direct measurement of exchange rates in the unfolded state, we were able to monitor hydrogen-bond formation for over 50 individual backbone NH groups within the initial 140 microseconds of folding of horse cytochrome c. Clusters of solvent-shielded amide protons were observed in two α-helical segments in the C-terminal half of the protein, while the N-terminal helix remained largely unstructured, suggesting that proximity in the primary structure is a major factor in promoting helix formation and association at early stages of folding, while the entropically more costly long-range contacts between the N- and C-terminal helices are established only during later stages. Our findings clearly indicate that the initial chain condensation in cytochrome c is driven by specific interactions among a subset of α-helical segments rather than a general hydrophobic collapse.
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Affiliation(s)
- Hossein Fazelinia
- Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, United States
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13
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Abstract
Kinetic folding of the large two-domain maltose binding protein (MBP; 370 residues) was studied at high structural resolution by an advanced hydrogen-exchange pulse-labeling mass-spectrometry method (HX MS). Dilution into folding conditions initiates a fast molecular collapse into a polyglobular conformation (<20 ms), determined by various methods including small angle X-ray scattering. The compaction produces a structurally heterogeneous state with widespread low-level HX protection and spectroscopic signals that match the equilibrium melting posttransition-state baseline. In a much slower step (7-s time constant), all of the MBP molecules, although initially heterogeneously structured, form the same distinct helix plus sheet folding intermediate with the same time constant. The intermediate is composed of segments that are distant in the MBP sequence but adjacent in the native protein where they close the longest residue-to-residue contact. Segments that are most HX protected in the early molecular collapse do not contribute to the initial intermediate, whereas the segments that do participate are among the less protected. The 7-s intermediate persists through the rest of the folding process. It contains the sites of three previously reported destabilizing mutations that greatly slow folding. These results indicate that the intermediate is an obligatory step on the MBP folding pathway. MBP then folds to the native state on a longer time scale (~100 s), suggestively in more than one step, the first of which forms structure adjacent to the 7-s intermediate. These results add a large protein to the list of proteins known to fold through distinct native-like intermediates in distinct pathways.
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14
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Kotamarthi HC, Sharma R, Narayan S, Ray S, Ainavarapu SRK. Multiple Unfolding Pathways of Leucine Binding Protein (LBP) Probed by Single-Molecule Force Spectroscopy (SMFS). J Am Chem Soc 2013; 135:14768-74. [DOI: 10.1021/ja406238q] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Hema Chandra Kotamarthi
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
| | - Riddhi Sharma
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
| | - Satya Narayan
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
| | - Sayoni Ray
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
| | - Sri Rama Koti Ainavarapu
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
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15
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Bouley Ford ND, Shin DW, Gray HB, Winkler JR. Intrachain contact dynamics in unfolded cytochrome cb562. J Phys Chem B 2013; 117:13206-11. [PMID: 23992117 DOI: 10.1021/jp403234h] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have investigated intrachain contact dynamics in unfolded cytochrome cb562 by monitoring heme quenching of excited ruthenium photosensitizers covalently bound to residues along the polypeptide. Intrachain diffusion for chemically denatured proteins proceeds on the microsecond time scale with an upper limit of 0.1 μs. The rate constants exhibit a power-law dependence on the number of peptide bonds between the heme and Ru complex. The power-law exponent of -1.5 is consistent with theoretical models for freely jointed Gaussian chains, but its magnitude is smaller than that reported for several synthetic polypeptides. Contact formation within a stable loop was examined in a His63-heme ligated form of the protein under denaturing conditions. Loop formation accelerated contact kinetics for the Ru66 labeling site, owing to reduction in the length of the peptide separating redox sites. For other labeling sites within the stable loop, quenching rates were modestly reduced compared to the open chain polymer.
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Affiliation(s)
- Nicole D Bouley Ford
- Beckman Institute, California Institute of Technology , Pasadena, California 91125, United States
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16
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Carvalho FA, Martins IC, Santos NC. Atomic force microscopy and force spectroscopy on the assessment of protein folding and functionality. Arch Biochem Biophys 2013; 531:116-27. [DOI: 10.1016/j.abb.2012.11.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Revised: 11/12/2012] [Accepted: 11/20/2012] [Indexed: 12/01/2022]
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