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Nijhawan AK, Leshchev D, Hsu DJ, Chan AM, Rimmerman D, Hong J, Kosheleva I, Henning R, Kohlstedt KL, Chen LX. Unlocking the unfolded structure of ubiquitin: Combining time-resolved x-ray solution scattering and molecular dynamics to generate unfolded ensembles. J Chem Phys 2024; 161:035101. [PMID: 39007394 PMCID: PMC11257700 DOI: 10.1063/5.0217013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2024] [Accepted: 06/04/2024] [Indexed: 07/16/2024] Open
Abstract
The unfolding dynamics of ubiquitin were studied using a combination of x-ray solution scattering (XSS) and molecular dynamics (MD) simulations. The kinetic analysis of the XSS ubiquitin signals showed that the protein unfolds through a two-state process, independent of the presence of destabilizing salts. In order to characterize the ensemble of unfolded states in atomic detail, the experimental XSS results were used as a constraint in the MD simulations through the incorporation of x-ray scattering derived potential to drive the folded ubiquitin structure toward sampling unfolded states consistent with the XSS signals. We detail how biased MD simulations provide insight into unfolded states that are otherwise difficult to resolve and underscore how experimental XSS data can be combined with MD to efficiently sample structures away from the native state. Our results indicate that ubiquitin samples unfolded in states with a high degree of loss in secondary structure yet without a collapse to a molten globule or fully solvated extended chain. Finally, we propose how using biased-MD can significantly decrease the computational time and resources required to sample experimentally relevant nonequilibrium states.
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Affiliation(s)
- Adam K. Nijhawan
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
| | - Denis Leshchev
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
| | - Darren J. Hsu
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
| | - Arnold M. Chan
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
| | - Dolev Rimmerman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
| | - Jiyun Hong
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
| | - Irina Kosheleva
- Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA
| | - Robert Henning
- Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA
| | - Kevin L. Kohlstedt
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
| | - Lin X. Chen
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
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2
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Henning RW, Kosheleva I, Šrajer V, Kim IS, Zoellner E, Ranganathan R. BioCARS: Synchrotron facility for probing structural dynamics of biological macromolecules. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2024; 11:014301. [PMID: 38304444 PMCID: PMC10834067 DOI: 10.1063/4.0000238] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/18/2023] [Accepted: 01/10/2024] [Indexed: 02/03/2024]
Abstract
A major goal in biomedical science is to move beyond static images of proteins and other biological macromolecules to the internal dynamics underlying their function. This level of study is necessary to understand how these molecules work and to engineer new functions and modulators of function. Stemming from a visionary commitment to this problem by Keith Moffat decades ago, a community of structural biologists has now enabled a set of x-ray scattering technologies for observing intramolecular dynamics in biological macromolecules at atomic resolution and over the broad range of timescales over which motions are functionally relevant. Many of these techniques are provided by BioCARS, a cutting-edge synchrotron radiation facility built under Moffat leadership and located at the Advanced Photon Source at Argonne National Laboratory. BioCARS enables experimental studies of molecular dynamics with time resolutions spanning from 100 ps to seconds and provides both time-resolved x-ray crystallography and small- and wide-angle x-ray scattering. Structural changes can be initiated by several methods-UV/Vis pumping with tunable picosecond and nanosecond laser pulses, substrate diffusion, and global perturbations, such as electric field and temperature jumps. Studies of dynamics typically involve subtle perturbations to molecular structures, requiring specialized computational techniques for data processing and interpretation. In this review, we present the challenges in experimental macromolecular dynamics and describe the current state of experimental capabilities at this facility. As Moffat imagined years ago, BioCARS is now positioned to catalyze the scientific community to make fundamental advances in understanding proteins and other complex biological macromolecules.
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Affiliation(s)
- Robert W. Henning
- BioCARS, Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA
| | - Irina Kosheleva
- BioCARS, Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA
| | - Vukica Šrajer
- BioCARS, Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA
| | - In-Sik Kim
- BioCARS, Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA
| | - Eric Zoellner
- BioCARS, Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA
| | - Rama Ranganathan
- BioCARS, Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA
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3
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Kosheleva I, Henning R, Kim I, Kim SO, Kusel M, Srajer V. Sample-minimizing co-flow cell for time-resolved pump-probe X-ray solution scattering. JOURNAL OF SYNCHROTRON RADIATION 2023; 30:490-499. [PMID: 36891863 PMCID: PMC10000795 DOI: 10.1107/s1600577522012127] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Accepted: 12/22/2022] [Indexed: 06/10/2023]
Abstract
A fundamental problem in biological sciences is understanding how macromolecular machines work and how the structural changes of a molecule are connected to its function. Time-resolved techniques are vital in this regard and essential for understanding the structural dynamics of biomolecules. Time-resolved small- and wide-angle X-ray solution scattering has the capability to provide a multitude of information about the kinetics and global structural changes of molecules under their physiological conditions. However, standard protocols for such time-resolved measurements often require significant amounts of sample, which frequently render time-resolved measurements impossible. A cytometry-type sheath co-flow cell, developed at the BioCARS 14-ID beamline at the Advanced Photon Source, USA, allows time-resolved pump-probe X-ray solution scattering measurements to be conducted with sample consumption reduced by more than ten times compared with standard sample cells and protocols. The comparative capabilities of the standard and co-flow experimental setups were demonstrated by studying time-resolved signals in photoactive yellow protein.
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Affiliation(s)
- Irina Kosheleva
- BioCARS, Center for Advanced Radiation Sources, The University of Chicago, 9700 South Cass Ave, Bld 434B, Lemont, IL 60439, USA
| | - Robert Henning
- BioCARS, Center for Advanced Radiation Sources, The University of Chicago, 9700 South Cass Ave, Bld 434B, Lemont, IL 60439, USA
| | - Insik Kim
- BioCARS, Center for Advanced Radiation Sources, The University of Chicago, 9700 South Cass Ave, Bld 434B, Lemont, IL 60439, USA
| | - Seong Ok Kim
- Department of Chemistry, Korea Advanced Institute of Science and Technology, E6-6 #513, 291 Daehak-ro, Daejeon, Yuseong-gu 34141, Republic of Korea
| | - Michael Kusel
- Kusel Design, 12 Coghlan Street, Niddrie, Wurundjeri Country 3042, Australia
| | - Vukica Srajer
- BioCARS, Center for Advanced Radiation Sources, The University of Chicago, 9700 South Cass Ave, Bld 434B, Lemont, IL 60439, USA
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4
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Chan AM, Nijhawan AK, Hsu DJ, Leshchev D, Rimmerman D, Kosheleva I, Kohlstedt KL, Chen LX. The Role of Transient Intermediate Structures in the Unfolding of the Trp-Cage Fast-Folding Protein: Generating Ensembles from Time-Resolved X-ray Solution Scattering with Genetic Algorithms. J Phys Chem Lett 2023; 14:1133-1139. [PMID: 36705525 PMCID: PMC10167713 DOI: 10.1021/acs.jpclett.2c03680] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
The Trp-cage miniprotein is one of the smallest systems to exhibit a stable secondary structure and fast-folding dynamics, serving as an apt model system to study transient intermediates with both experimental and computational analyses. Previous spectroscopic characterizations that have been done on Trp-cage have inferred a single stable intermediate on a pathway from folded to unfolded basins. We aim to bridge the understanding of Trp-cage structural folding dynamics on microsecond-time scales, by utilizing time-resolved X-ray solution scattering to probe the temperature-induced unfolding pathway. Our results indicate the formation of a conformationally extended intermediate on the time scale of 1 μs, which undergoes complete unfolding within 5 μs. We further investigated the atomistic structural details of the unfolding pathway using a genetic algorithm to generate ensemble model fits to the scattering profiles. This analysis paves the way for direct benchmarking of theoretical models of protein folding ensembles produced with molecular dynamics simulations.
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Affiliation(s)
- Arnold M Chan
- Department of Chemistry, Northwestern University, Evanston, Illinois60208, United States
| | - Adam K Nijhawan
- Department of Chemistry, Northwestern University, Evanston, Illinois60208, United States
| | - Darren J Hsu
- Department of Chemistry, Northwestern University, Evanston, Illinois60208, United States
| | - Denis Leshchev
- Department of Chemistry, Northwestern University, Evanston, Illinois60208, United States
| | - Dolev Rimmerman
- Department of Chemistry, Northwestern University, Evanston, Illinois60208, United States
| | - Irina Kosheleva
- Center for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois60637, United States
| | - Kevin L Kohlstedt
- Department of Chemistry, Northwestern University, Evanston, Illinois60208, United States
| | - Lin X Chen
- Department of Chemistry, Northwestern University, Evanston, Illinois60208, United States
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois60439, United States
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5
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Gupta MN, Uversky VN. Pre-Molten, Wet, and Dry Molten Globules en Route to the Functional State of Proteins. Int J Mol Sci 2023; 24:ijms24032424. [PMID: 36768742 PMCID: PMC9916686 DOI: 10.3390/ijms24032424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2022] [Revised: 01/23/2023] [Accepted: 01/23/2023] [Indexed: 01/28/2023] Open
Abstract
Transitions between the unfolded and native states of the ordered globular proteins are accompanied by the accumulation of several intermediates, such as pre-molten globules, wet molten globules, and dry molten globules. Structurally equivalent conformations can serve as native functional states of intrinsically disordered proteins. This overview captures the characteristics and importance of these molten globules in both structured and intrinsically disordered proteins. It also discusses examples of engineered molten globules. The formation of these intermediates under conditions of macromolecular crowding and their interactions with nanomaterials are also reviewed.
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Affiliation(s)
- Munishwar Nath Gupta
- Department of Biochemical Engineering and Biotechnology, Indian Institute of Technology, Hauz Khas, New Delhi 110016, India
| | - Vladimir N. Uversky
- Department of Molecular Medicine and USF Health Byrd Alzheimer’s Research Institute, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA
- Correspondence: ; Tel.: +1-813-494-5816
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6
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Bhattacharjee R, Udgaonkar JB. Differentiating between the sequence of structural events on alternative pathways of folding of a heterodimeric protein. Protein Sci 2022; 31:e4513. [PMID: 36382901 PMCID: PMC9703597 DOI: 10.1002/pro.4513] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2022] [Revised: 11/09/2022] [Accepted: 11/10/2022] [Indexed: 11/17/2022]
Abstract
Distinguishing between competing pathways of folding of a protein, on the basis of how they differ in their progress of structure acquisition, remains an important challenge in protein folding studies. A previous study had shown that the heterodimeric protein, double chain monellin (dcMN) switches between alternative folding pathways upon a change in guanidine hydrochloride (GdnHCl) concentration. In the current study, the folding of dcMN has been characterized by the pulsed hydrogen exchange (HX) labeling methodology used in conjunction with mass spectrometry. Quantification of the extent to which folding intermediates accumulate and then disappear with time of folding at both low and high GdnHCl concentrations, where the folding pathways are known to be different, shows that the folding mechanism is describable by a triangular three-state mechanism. Structural characterization of the productive folding intermediates populated on the alternative pathways has enabled the pathways to be differentiated on the basis of the progress of structure acquisition that occurs on them. The intermediates on the two pathways differ in the extent to which the α-helix and the rest of the β-sheet have acquired structure that is protective against HX. The major difference is, however, that β2 has not acquired any protective structure in the intermediate formed on one pathway, but it has acquired significant protective structure in the intermediate formed on the alternative pathway. Hence, the sequence of structural events is different on the two alternative pathways.
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Affiliation(s)
- Rupam Bhattacharjee
- National Centre for Biological Sciences, Tata Institute of Fundamental ResearchBengaluruKarnatakaIndia
- Indian Institute of Science Education and ResearchPuneMaharashtraIndia
| | - Jayant B. Udgaonkar
- National Centre for Biological Sciences, Tata Institute of Fundamental ResearchBengaluruKarnatakaIndia
- Indian Institute of Science Education and ResearchPuneMaharashtraIndia
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7
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Chatzimagas L, Hub JS. Structure and ensemble refinement against SAXS data: Combining MD simulations with Bayesian inference or with the maximum entropy principle. Methods Enzymol 2022; 678:23-54. [PMID: 36641209 DOI: 10.1016/bs.mie.2022.09.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Small-angle X-ray scattering (SAXS) is a powerful method for tracking conformational transitions of proteins or soft-matter complexes in solution. However, the interpretation of the experimental data is challenged by the low spatial resolution and the low information content of the data, which lead to a high risk of overinterpreting the data. Here, we illustrate how SAXS data can be integrated into all-atom molecular dynamics (MD) simulation to derive atomic structures or heterogeneous ensembles that are compatible with the data. Besides providing atomistic insight, the MD simulation adds physicochemical information, as encoded in the MD force fields, which greatly reduces the risk of overinterpretation. We present an introduction into the theory of SAXS-driven MD simulations as implemented in GROMACS-SWAXS, a modified version of the GROMACS simulation software. We discuss SAXS-driven parallel-replica ensemble refinement with commitment to the maximum entropy principle as well as a Bayesian formulation of SAXS-driven structure refinement. Practical considerations for running and interpreting the simulations are presented. The methods are freely available via GitLab at https://gitlab.com/cbjh/gromacs-swaxs.
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Affiliation(s)
- Leonie Chatzimagas
- Theoretical Physics and Center for Biophysics, Saarland University, Saarbrücken, Germany
| | - Jochen S Hub
- Theoretical Physics and Center for Biophysics, Saarland University, Saarbrücken, Germany.
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8
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Sun Y, Li X, Chen R, Liu F, Wei S. Recent advances in structural characterization of biomacromolecules in foods via small-angle X-ray scattering. Front Nutr 2022; 9:1039762. [PMID: 36466419 PMCID: PMC9714470 DOI: 10.3389/fnut.2022.1039762] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Accepted: 11/03/2022] [Indexed: 08/04/2023] Open
Abstract
Small-angle X-ray scattering (SAXS) is a method for examining the solution structure, oligomeric state, conformational changes, and flexibility of biomacromolecules at a scale ranging from a few Angstroms to hundreds of nanometers. Wide time scales ranging from real time (milliseconds) to minutes can be also covered by SAXS. With many advantages, SAXS has been extensively used, it is widely used in the structural characterization of biomacromolecules in food science and technology. However, the application of SAXS in charactering the structure of food biomacromolecules has not been reviewed so far. In the current review, the principle, theoretical calculations and modeling programs are summarized, technical advances in the experimental setups and corresponding applications of in situ capabilities: combination of chromatography, time-resolved, temperature, pressure, flow-through are elaborated. Recent applications of SAXS for monitoring structural properties of biomacromolecules in food including protein, carbohydrate and lipid are also highlighted, and limitations and prospects for developing SAXS based on facility upgraded and artificial intelligence to study the structural properties of biomacromolecules are finally discussed. Future research should focus on extending machine time, simplifying SAXS data treatment, optimizing modeling methods in order to achieve an integrated structural biology based on SAXS as a practical tool for investigating the structure-function relationship of biomacromolecules in food industry.
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Affiliation(s)
- Yang Sun
- College of Vocational and Technical Education, Yunnan Normal University, Kunming, China
| | - Xiujuan Li
- Pharmaceutical Department, The Affiliated Taian City Central Hospital of Qingdao University, Taian, China
| | - Ruixin Chen
- College of Vocational and Technical Education, Yunnan Normal University, Kunming, China
| | - Fei Liu
- College of Vocational and Technical Education, Yunnan Normal University, Kunming, China
| | - Song Wei
- Tumor Precise Intervention and Translational Medicine Laboratory, The Affiliated Taian City Central Hospital of Qingdao University, Taian, China
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9
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Beyond particle stabilization of emulsions and foams: Proteins in liquid-liquida and liquid-gas interfaces. Adv Colloid Interface Sci 2022; 308:102743. [DOI: 10.1016/j.cis.2022.102743] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2022] [Revised: 07/04/2022] [Accepted: 07/15/2022] [Indexed: 01/02/2023]
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10
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Caporaletti F, Bittermann MR, Bonn D, Woutersen S. Fluorescent molecular rotor probes nanosecond viscosity changes. J Chem Phys 2022; 156:201101. [DOI: 10.1063/5.0092248] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Viscosity is a key property of liquids, but it is difficult to measure in short-lived, metastable samples due to the long measuring times required by conventional rheology. Here, we show how this problem can be solved by using fluorescent molecular rotors. The excited-state fluorescence decay rate of these molecules is sensitive to the viscosity of their local environment, and by combining pulsed laser excitation with time-resolved fluorescence detection, we can measure viscosities with a time resolution of a few ns. We demonstrate this by measuring in real time the viscosity change in glycerol induced by a nanosecond temperature jump. This new approach makes it possible to measure the viscosity of extremely short-lived states of matter.
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Affiliation(s)
- Federico Caporaletti
- Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, 1098XH Amsterdam, The Netherlands
- Van ’t Hoff Institute for Molecular Sciences, University of Amsterdam, 1098XH Amsterdam, The Netherlands
| | - Marius R. Bittermann
- Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, 1098XH Amsterdam, The Netherlands
| | - Daniel Bonn
- Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, 1098XH Amsterdam, The Netherlands
| | - Sander Woutersen
- Van ’t Hoff Institute for Molecular Sciences, University of Amsterdam, 1098XH Amsterdam, The Netherlands
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11
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Nijhawan AK, Chan AM, Hsu DJ, Chen LX, Kohlstedt KL. Resolving Dynamics in the Ensemble: Finding Paths through Intermediate States and Disordered Protein Structures. J Phys Chem B 2021; 125:12401-12412. [PMID: 34748336 PMCID: PMC9096987 DOI: 10.1021/acs.jpcb.1c05820] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Proteins have been found to inhabit a diverse set of three-dimensional structures. The dynamics that govern protein interconversion between structures happen over a wide range of time scales─picoseconds to seconds. Our understanding of protein functions and dynamics is largely reliant upon our ability to elucidate physically populated structures. From an experimental structural characterization perspective, we are often limited to measuring the ensemble-averaged structure both in the steady-state and time-resolved regimes. Generating kinetic models and understanding protein structure-function relationships require atomistic knowledge of the populated states in the ensemble. In this Perspective, we present ensemble refinement methodologies that integrate time-resolved experimental signals with molecular dynamics models. We first discuss integration of experimental structural restraints to molecular models in disordered protein systems that adhere to the principle of maximum entropy for creating a complete set of ensemble structures. We then propose strategies to find kinetic pathways between the refined structures, using time-resolved inputs to guide molecular dynamics trajectories and the use of inference to generate tailored stimuli to prepare a desired ensemble of protein states.
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Affiliation(s)
- Adam K Nijhawan
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
| | - Arnold M Chan
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
| | - Darren J Hsu
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
| | - Lin X Chen
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - Kevin L Kohlstedt
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
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12
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Cai S, Kumar R, Singh BR. Clostridial Neurotoxins: Structure, Function and Implications to Other Bacterial Toxins. Microorganisms 2021; 9:2206. [PMID: 34835332 PMCID: PMC8618262 DOI: 10.3390/microorganisms9112206] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Revised: 10/19/2021] [Accepted: 10/19/2021] [Indexed: 01/20/2023] Open
Abstract
Gram-positive bacteria are ancient organisms. Many bacteria, including Gram-positive bacteria, produce toxins to manipulate the host, leading to various diseases. While the targets of Gram-positive bacterial toxins are diverse, many of those toxins use a similar mechanism to invade host cells and exert their functions. Clostridial neurotoxins produced by Clostridial tetani and Clostridial botulinum provide a classical example to illustrate the structure-function relationship of bacterial toxins. Here, we critically review the recent progress of the structure-function relationship of clostridial neurotoxins, including the diversity of the clostridial neurotoxins, the mode of actions, and the flexible structures required for the activation of toxins. The mechanism clostridial neurotoxins use for triggering their activity is shared with many other Gram-positive bacterial toxins, especially molten globule-type structures. This review also summarizes the implications of the molten globule-type flexible structures to other Gram-positive bacterial toxins. Understanding these highly dynamic flexible structures in solution and their role in the function of bacterial toxins not only fills in the missing link of the high-resolution structures from X-ray crystallography but also provides vital information for better designing antidotes against those toxins.
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Affiliation(s)
- Shuowei Cai
- Department of Chemistry and Biochemistry, University of Massachusetts Dartmouth, Dartmouth, MA 02747, USA
| | - Raj Kumar
- Botulinum Research Center, Institute of Advanced Sciences, Dartmouth, MA 02747, USA; (R.K.); (B.R.S.)
| | - Bal Ram Singh
- Botulinum Research Center, Institute of Advanced Sciences, Dartmouth, MA 02747, USA; (R.K.); (B.R.S.)
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13
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Haller N, Maier I, Kulozik U. Molecular Analytical Assessment of Thermally Precipitated α-Lactalbumin after Resolubilization. Foods 2021; 10:foods10092231. [PMID: 34574341 PMCID: PMC8465387 DOI: 10.3390/foods10092231] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2021] [Revised: 09/12/2021] [Accepted: 09/15/2021] [Indexed: 11/24/2022] Open
Abstract
Selective thermal precipitation followed by a mechanical separation step is a well described method for fractionation of the main whey proteins, α-lactalbumin (α-la) and β-lactoglobulin (β-lg). By choosing appropriate environmental conditions the thermal precipitation of either α-la or β-lg can be induced. Whereas β-lg irreversibly aggregates, the precipitated α-la can be resolubilized by a subsequent adjustment of the solution’s pH and the ionic composition. This study reports on the analytical characterization of resolubilized α-la compared to its native counterpart as a reference in order to assess whether the resolubilized α-la can be considered close to ‘native’. Turbidity and quantification by RP-HPLC of the resolubilized α-la solutions were used as a measure of solubility in aqueous environment. RP-HPLC was also applied to determine the elution time as a measure for protein’s hydrophobicity. DSC measurement was performed to determine the denaturation peak temperature of resolubilized α-la. FTIR spectroscopy provided insights in the secondary structure. The refolding of α-la achieved best results using pH 8.0 and a 3-fold stoichiometric amount of Ca2+ per α-la molecule. The results showed that the mechanism of aggregation induced by gentle thermal treatment under acidic conditions with subsequent mechanical separation is reversible to a certain extent, however, the exact native conformation was not restored.
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14
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Filming ultrafast roaming-mediated isomerization of bismuth triiodide in solution. Nat Commun 2021; 12:4732. [PMID: 34354075 PMCID: PMC8342516 DOI: 10.1038/s41467-021-25070-z] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Accepted: 07/20/2021] [Indexed: 12/19/2022] Open
Abstract
Roaming reaction, defined as a reaction yielding products via reorientational motion in the long-range region (3 - 8 Å) of the potential, is a relatively recently proposed reaction pathway and is now regarded as a universal mechanism that can explain the unimolecular dissociation and isomerization of various molecules. The structural movements of the partially dissociated fragments originating from the frustrated bond fission at the onset of roaming, however, have been explored mostly via theoretical simulations and rarely observed experimentally. Here, we report an investigation of the structural dynamics during a roaming-mediated isomerization reaction of bismuth triiodide (BiI3) in acetonitrile solution using femtosecond time-resolved x-ray liquidography. Structural analysis of the data visualizes the atomic movements during the roaming-mediated isomerization process including the opening of the Bi-Ib-Ic angle and the closing of Ia-Bi-Ib-Ic dihedral angle, each by ~40°, as well as the shortening of the Ib···Ic distance, following the frustrated bond fission.
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