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Unfolded Lipase at Interfaces Studied via Interfacial Dilational Rheology: The Impact of Urea. COLLOIDS AND INTERFACES 2022. [DOI: 10.3390/colloids6040056] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Unfolding can interrupt the activity of enzymes. Lipase, the enzyme responsible for triglyceride catalysis, can be deactivated by unfolding, which can significantly affect the yield of enzymatic processes in biochemical engineering. Different agents can induce lipase unfolding, among which we study the impact of urea as a strong denaturant. Unfolding weakens the rigidity and stability of globular proteins, thereby changing the viscoelastic properties of the protein adsorbed layers. These changes can be detected and quantified using interfacial dilational rheology. The urea-induced unfolding of lipase destructs its globular structure, making it more flexible. The interfacial tension and viscoelastic moduli of lipase adsorbed layers reduce upon the addition of urea in the range of studied concentrations. The results agree with the theory that, upon unfolding, a distal region of the loop and tail domain forms adjacent to the proximal region of the interface. The exchange of matter between these regions reduces the viscoelasticity of the unfolded lipase adsorbed layers. Additionally, unfolding reduces the rigidity and brittleness of the lipase adsorbed layers: the aged adsorbed layer of native lipase can break upon high-amplitude perturbations of the interfacial area, unlike the case for urea-induced unfolded lipase.
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Bonarek P, Loch JI, Tworzydło M, Cooper DR, Milto K, Wróbel P, Kurpiewska K, Lewiński K. Structure-based design approach to rational site-directed mutagenesis of β-lactoglobulin. J Struct Biol 2020; 210:107493. [PMID: 32169624 DOI: 10.1016/j.jsb.2020.107493] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Revised: 03/06/2020] [Accepted: 03/09/2020] [Indexed: 12/30/2022]
Abstract
Recombinant proteins play an important role in medicine and have diverse applications in industrial biotechnology. Lactoglobulin has shown great potential for use in targeted drug delivery and body fluid detoxification because of its ability to bind a variety of molecules. In order to modify the biophysical properties of β-lactoglobulin, a series of single-site mutations were designed using a structure-based approach. A 3-dimensional structure alignment of homologous molecules led to the design of nine β-lactoglobulin variants with mutations introduced in the binding pocket region. Seven stable and correctly folded variants (L39Y, I56F, L58F, V92F, V92Y, F105L, M107L) were thoroughly characterized by fluorescence, circular dichroism, isothermal titration calorimetry, size-exclusion chromatography, and X-ray structural investigations. The effects of the amino acid substitutions were observed as slight rearrangements of the binding pocket geometry, but they also significantly influenced the global properties of the protein. Most of the mutations increased the thermal/chemical stability without altering the dimerization constant or pH-dependent conformational behavior. The crystal structures reveal that the I56F and F105L mutations reduced the depth of the binding pocket, which is advantageous since it can reduce the affinity to endogenous fatty acids. The F105L mutant created a unique binding mode for a fatty acid, supporting the idea that lactoglobulin can be altered to bind unique molecules. Selected variants possessing a unique combination of their individual properties can be used for further, more advanced mutagenesis, and the presented results support further research using β-lactoglobulin as a therapeutic delivery agent or a blood detoxifying molecule.
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Affiliation(s)
- Piotr Bonarek
- Jagiellonian University, Faculty of Biochemistry, Biophysics and Biotechnology, Gronostajowa 7, 30-387 Kraków, Poland
| | - Joanna I Loch
- Jagiellonian University, Faculty of Chemistry, Gronostajowa 2, 30-387 Kraków, Poland
| | - Magdalena Tworzydło
- Jagiellonian University, Faculty of Biochemistry, Biophysics and Biotechnology, Gronostajowa 7, 30-387 Kraków, Poland
| | - David R Cooper
- University of Virginia, Department of Molecular Physiology and Biological Physics, 1340 Jefferson Park Avenue, Charlottesville, VA 22908, USA
| | - Katažyna Milto
- Jagiellonian University, Faculty of Biochemistry, Biophysics and Biotechnology, Gronostajowa 7, 30-387 Kraków, Poland
| | - Paulina Wróbel
- Jagiellonian University, Faculty of Chemistry, Gronostajowa 2, 30-387 Kraków, Poland
| | - Katarzyna Kurpiewska
- Jagiellonian University, Faculty of Chemistry, Gronostajowa 2, 30-387 Kraków, Poland
| | - Krzysztof Lewiński
- Jagiellonian University, Faculty of Chemistry, Gronostajowa 2, 30-387 Kraków, Poland.
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Patel BK, Sepay N, Mahapatra A. Curious Results in the Prospective Binding Interactions of the Food Additive Tartrazine with β-Lactoglobulin. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:11579-11589. [PMID: 31385703 DOI: 10.1021/acs.langmuir.9b01242] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The detailed characterizations of the binding interactions between food additive tartrazine (TZ) and β-lactoglobulin (β-LG) have been investigated through spectroscopic techniques combined with a molecular modeling study. A series of analyses, such as hyperchromic change in the UV-visible spectra, temperature-dependent quenching constant, time-resolved fluorescence, and Rayleigh scattering measurements, show that quenching of β-LG proceeds by a static quenching mechanism. TZ specifically binds with β-LG in a stoichiometry ratio of 1:1, and the observed binding constants (104, K) are 7.64, 9.13, 9.72, and 10.79 at 293, 298, 303, and 308 K, respectively. However, the curious results of binding constants (K) with temperature, encountered in the static quenching, have been well explained on the basis of Le Chatelier's principle. Thermodynamic data and pH-dependent studies along with the surface hydrophobicity binding displacement assay reveal that the durable mode of binding is chiefly entropy-driven, revealing noteworthy interactions of such ionic molecules with the hydrophobic part of β-LG. The modulation of protein conformation has been investigated through steady-state absorption spectroscopy, synchronous emission spectroscopy, circular dichroism, and dynamic light scattering studies. TZ acts as a potential inhibitor in fibrillogenesis. Furthermore, the molecular docking study offers accurate insights about the binding of TZ with β-LG, in consistence with the experimental results. This study would be helpful in pharmaceutical, food, and industrial engineering chemistry research.
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Affiliation(s)
- Biman Kumar Patel
- Department of Chemistry , Jadavpur University , Kolkata 700 032 , India
| | - Nayim Sepay
- Department of Chemistry , Jadavpur University , Kolkata 700 032 , India
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Pandey P, Meena NK, Prakash A, Kumar V, Lynn AM, Ahmad F. Characterization of heterogeneous intermediate ensembles on the guanidinium chloride-induced unfolding pathway of β-lactoglobulin. J Biomol Struct Dyn 2019; 38:1042-1053. [PMID: 30880641 DOI: 10.1080/07391102.2019.1593245] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Folding pathway of β-LgA (β-lactoglobulin) evolves through the conformational α→β transition. The α→β transition is a molecular hallmark of various neurodegenerative diseases. Thus, β-LgA may serve as a good model for understanding molecular mechanism of protein aggregation involved in neurodegenerative diseases. Here, we studied the conformational dynamics of β-LgA in 6 M GdmCl at different temperatures using MD simulations. Structural order parameters such as RMSD, Rg, SASA, native contacts (Q), hydrophobic distal-matrix and free-energy landscape (FEL) were used to investigate the conformational transitions. Our results show that GdmCl destabilizes secondary and tertiary structure of β-LgA by weakening the hydrophobic interactions and hydrogen bond network. Multidimensional FEL shows the presence of different unfolding intermediates at 400 K. I1 is long-lived intermediate which has mostly intact native secondary structure, but loose tertiary structure. I2 is structurally compact intermediate formed after the partial loss of secondary structure. The transiently and infrequently buried evolution of W19 shows that intermediate conformational ensembles are structurally heterogeneous. We observed that the intermediate conformations are largely stabilized by non-native H-bonds. The outcome of this work provides the molecular details of intermediates trapped due to non-native interactions that may be regarded as pathogenic conformations involved in neurodegenerative diseases.Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Preeti Pandey
- School of Computational & Integrative Sciences, Jawaharlal Nehru University, New Delhi, India
| | - Naveen Kumar Meena
- School of Computational & Integrative Sciences, Jawaharlal Nehru University, New Delhi, India
| | - Amresh Prakash
- School of Computational & Integrative Sciences, Jawaharlal Nehru University, New Delhi, India
| | - Vijay Kumar
- Amity Institute of Neuropsychology & Neurosciences, Amity University, Noida, India
| | - Andrew M Lynn
- School of Computational & Integrative Sciences, Jawaharlal Nehru University, New Delhi, India
| | - Faizan Ahmad
- Jamia Millia Islamia, Centre for Interdisciplinary Research in Basic Sciences, New Delhi, India
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5
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Sindhu A, Mogha NK, Venkatesu P. Insight into impact of choline-based ionic liquids on bovine β-lactoglobulin structural analysis: Unexpected high thermal stability of protein. Int J Biol Macromol 2019; 126:1-10. [DOI: 10.1016/j.ijbiomac.2018.12.166] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2018] [Revised: 12/17/2018] [Accepted: 12/18/2018] [Indexed: 10/27/2022]
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6
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Sengupta B, Das N, Sen P. Monomerization and aggregation of β-lactoglobulin under adverse condition: A fluorescence correlation spectroscopic investigation. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2018; 1866:316-326. [DOI: 10.1016/j.bbapap.2017.11.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2017] [Revised: 11/01/2017] [Accepted: 11/12/2017] [Indexed: 12/26/2022]
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7
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Rudra S, Jana A, Sepay N, Patel BK, Mahapatra A. Characterization of the binding of strychnine with bovine β-lactoglobulin and human lysozyme using spectroscopic, kinetic and molecular docking analysis. NEW J CHEM 2018. [DOI: 10.1039/c8nj00810h] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The binding interaction of a well known alkaloid strychnine (STN) with the mammalian milk protein β-lactoglobulin and human lysozyme has been explored by using several spectroscopic techniques along with computational studies.
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Affiliation(s)
- Suparna Rudra
- Department of Chemistry
- Jadavpur University
- Kolkata 700032
- India
| | - Abhisek Jana
- Department of Chemistry
- Jadavpur University
- Kolkata 700032
- India
| | - Nayim Sepay
- Department of Chemistry
- Jadavpur University
- Kolkata 700032
- India
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8
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Engineered β-Lactoglobulin Produced in E. coli: Purification, Biophysical and Structural Characterisation. Mol Biotechnol 2016; 58:605-618. [PMID: 27380951 PMCID: PMC5035327 DOI: 10.1007/s12033-016-9960-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Functional recombinant bovine β-lactoglobulin has been produced by expression in E. coli using an engineered protein gene and purified to homogeneity by applying a new protocol. Mutations L1A/I2S introduced into the protein sequence greatly facilitate in vivo cleavage of the N-terminal methionine, allowing correctly folded and soluble protein suitable for biochemical, biophysical and structural studies to be obtained. The use of gel filtration on Sephadex G75 at the last purification step enables protein without endogenous ligand to be obtained. The physicochemical properties of recombinant β-lactoglobulin such as CD spectra, ligand binding (n, K a, ΔH, TΔS, ΔG), chemical and thermal stability (ΔG D, C mid) and crystal structure confirmed that the protein obtained is almost identical to the natural one. The substitutions of N-terminal residues did not influence the binding properties of the recombinant protein so that the lactoglobulin produced and purified according to our protocol is a good candidate for further engineering and potential use in pharmacology and medicine.
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10
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de Kort BJ, de Jong GJ, Somsen GW. Potential of capillary electrophoresis with wavelength-resolved fluorescence detection for protein unfolding studies using β-lactoglobulin B as a test compound. Analyst 2013; 138:4550-7. [DOI: 10.1039/c3an00357d] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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11
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Electrostatics of folded and unfolded bovine β-lactoglobulin. Amino Acids 2011; 42:2019-30. [DOI: 10.1007/s00726-011-0933-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Accepted: 04/30/2011] [Indexed: 11/26/2022]
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12
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Seo JA, Hédoux A, Guinet Y, Paccou L, Affouard F, Lerbret A, Descamps M. Thermal denaturation of beta-lactoglobulin and stabilization mechanism by trehalose analyzed from Raman spectroscopy investigations. J Phys Chem B 2010; 114:6675-84. [PMID: 20411964 DOI: 10.1021/jp1006022] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The thermal denaturation process of beta-lactoglobulin has been analyzed in the 20-100 degrees C temperature range by Raman spectroscopy experiments simultaneously performed in the region of amide modes (800-1800 cm(-1)) and in the low-frequency range (10-350 cm(-1)). The analysis of amide modes reveals a two-step thermal denaturation process in the investigated temperature range. The first step corresponds to the dissociation of dimers associated with an increase of flexibility of the tertiary structure. In the second step, large conformational changes are detected in the secondary structure and described as a loss of alpha-helix structures and a concomitant formation of beta-sheets. Raman investigations in the low-frequency range provide important information on the origin of the denaturation process through the analysis of the solvent dynamics and its coupling with that of the protein. The softening of the tetrahedral structure of water induces the dissociation of dimers and makes the tertiary structure softer, leading to the water penetration in the protein interior. The methodology based on Raman investigations of amide modes and in the low-frequency region was used to analyze the mechanism of beta-lactoglobulin thermostabilization by trehalose. The main effect of trehalose is determined to be related to its capabilities to distort the tetrahedral organization of water molecules.
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Affiliation(s)
- Jeong-Ah Seo
- Unité Matériaux Et Transformations, UMR CNRS 8207, Université de Lille 1, 59655 Villeneuve d Ascq Cédex, France
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13
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Yan W, Qiao L, Gu X, Li J, Xu R, Wang M, Reuhs B, Yang Y. Effect of high pressure treatment on the physicochemical and functional properties of egg yolk. Eur Food Res Technol 2010. [DOI: 10.1007/s00217-010-1286-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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14
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Paul BK, Samanta A, Guchhait N. Exploring Hydrophobic Subdomain IIA of the Protein Bovine Serum Albumin in the Native, Intermediate, Unfolded, and Refolded States by a Small Fluorescence Molecular Reporter. J Phys Chem B 2010; 114:6183-96. [DOI: 10.1021/jp100004t] [Citation(s) in RCA: 167] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Bijan Kumar Paul
- Department of Chemistry, University of Calcutta, 92 A. P. C. Road, Calcutta 700009, India
| | - Anuva Samanta
- Department of Chemistry, University of Calcutta, 92 A. P. C. Road, Calcutta 700009, India
| | - Nikhil Guchhait
- Department of Chemistry, University of Calcutta, 92 A. P. C. Road, Calcutta 700009, India
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15
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Suresh A, Karthikraja V, Lulu S, Kangueane U, Kangueane P. A decision tree model for the prediction of homodimer folding mechanism. Bioinformation 2009; 4:197-205. [PMID: 20461159 PMCID: PMC2859576 DOI: 10.6026/97320630004197] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2009] [Accepted: 11/09/2009] [Indexed: 11/25/2022] Open
Abstract
The formation of protein homodimer complexes for molecular catalysis and regulation is fascinating. The homodimer formation through 2S (2 state), 3SMI (3 state with monomer intermediate) and 3SDI (3 state with dimer intermediate) folding mechanism is known for 47 homodimer structures. Our dataset of forty-seven homodimers consists of twenty-eight 2S, twelve 3SMI and seven 3SDI. The dataset is characterized using monomer length, interface area and interface/total (I/T) residue ratio. It is found that 2S are often small in size with large I/T ratio and 3SDI are frequently large in size with small I/T ratio. Nonetheless, 3SMI have a mixture of these features. Hence, we used these parameters to develop a decision tree model. The decision tree model produced positive predictive values (PPV) of 72% for 2S, 58% for 3SMI and 57% for 3SDI in cross validation. Thus, the method finds application in assigning homodimers with folding mechanism.
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Affiliation(s)
- Abishek Suresh
- Biomedical Informatics, Pondicherry 607402
- AIMST University, Semeling 08100, Malaysia
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16
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Silva I, Sansone S, Brancaleon L. An Anionic Porphyrin Binds β-Lactoglobulin A at a Superficial Site Rich in Lysine Residues. Protein J 2009; 28:1-13. [DOI: 10.1007/s10930-008-9158-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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17
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Czarnik-Matusewicz B, Kim SB, Jung YM. A Study of Urea-dependent Denaturation of β-Lactoglobulin by Principal Component Analysis and Two-dimensional Correlation Spectroscopy. J Phys Chem B 2008; 113:559-66. [DOI: 10.1021/jp808396g] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Bogusława Czarnik-Matusewicz
- Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland, Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea, and Department of Chemistry, Kangwon National University, Chunchon 200-701, Korea
| | - Seung Bin Kim
- Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland, Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea, and Department of Chemistry, Kangwon National University, Chunchon 200-701, Korea
| | - Young Mee Jung
- Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland, Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea, and Department of Chemistry, Kangwon National University, Chunchon 200-701, Korea
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18
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Stability of β-Lactoglobulin A in the Presence of Sugar Osmolytes Estimated from Their Guanidinium Chloride-Induced Transition Curves. Protein J 2008; 27:455-60. [DOI: 10.1007/s10930-008-9156-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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19
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Santambrogio C, Grandori R. Monitoring the Tanford transition in beta-lactoglobulin by 8-anilino-1-naphthalene sulfonate and mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2008; 22:4049-4054. [PMID: 19016256 DOI: 10.1002/rcm.3824] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The fluorescent dye 8-anilino-1-naphthalene sulfonate (ANS) is known to interact with proteins by conformation-specific hydrophobic interactions and rather nonspecific electrostatic interactions. To which category the complexes detectable by mass spectrometry (MS) belong is still the subject of debate. Here, the Tanford transition in beta-lactoglobulin (BLG) is exploited as an experimental device to expose hydrophobic binding sites by an increase in pH, rather than, as usually done, by lowering the pH. Complex formation is monitored by electrospray ionization (ESI)-MS and fluorescence spectroscopy. Both techniques reveal stronger ANS binding to BLG at pH 7.9 than at pH 5.9, suggesting that dye binding inside the calyx, which is known to be hydrophobically driven in solution, can contribute to the complexes detected by ESI-MS. Electrostatic interactions between the protein and the ANS sulfonate group can only be weaker at pH 7.9 than at pH 5.9, supporting the interpretation of the results by the protein conformational change. Lysozyme is used as a negative control, which shows no variation in the interaction with ANS in the same range of pH, in the absence of conformational changes. However, comparison of MS and fluorescence data at variable pH for BLG and myoglobin (Mb) suggests that conformation-specific ANS binding to proteins is detectable by ESI-MS only inside well-structured cavities of folded structures, like the BLG calyx and apoMb heme pocket. Indeed, ANS interactions with highly dynamic structures or molten globules, although detectable in solution, are easily lost in the gas phase.
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Affiliation(s)
- Carlo Santambrogio
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milan, Italy
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Giurleo JT, He X, Talaga DS. β-Lactoglobulin Assembles into Amyloid through Sequential Aggregated Intermediates. J Mol Biol 2008; 381:1332-48. [DOI: 10.1016/j.jmb.2008.06.043] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2008] [Revised: 05/22/2008] [Accepted: 06/16/2008] [Indexed: 10/21/2022]
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21
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Wang XS, Tang CH, Li BS, Yang XQ, Li L, Ma CY. Effects of high-pressure treatment on some physicochemical and functional properties of soy protein isolates. Food Hydrocoll 2008. [DOI: 10.1016/j.foodhyd.2007.01.027] [Citation(s) in RCA: 196] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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22
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Giurleo JT, Talaga DS. Global fitting without a global model: regularization based on the continuity of the evolution of parameter distributions. J Chem Phys 2008; 128:114114. [PMID: 18361561 DOI: 10.1063/1.2837293] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We introduce a new approach to global data fitting based on a regularization condition that invokes continuity in the global data coordinate. Stabilization of the data fitting procedure comes from probabilistic constraint of the global solution to physically reasonable behavior rather than to specific models of the system behavior. This method is applicable to the fitting of many types of spectroscopic data including dynamic light scattering, time-correlated single-photon counting (TCSPC), and circular dichroism. We compare our method to traditional approaches to fitting an inverse Laplace transform by examining the evolution of multiple lifetime components in synthetic TCSPC data. The global regularizer recovers features in the data that are not apparent from traditional fitting. We show how our approach allows one to start from an essentially model-free fit and progress to a specific model by moving from probabilistic to deterministic constraints in both Laplace transformed and nontransformed coordinates.
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Affiliation(s)
- Jason T Giurleo
- Department of Chemistry and Chemical Biology and BIOMAPS Institute, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA
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23
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Perriman AW, Henderson MJ, Holt SA, White JW. Effect of the Air−Water Interface on the Stability of β-Lactoglobulin. J Phys Chem B 2007; 111:13527-37. [DOI: 10.1021/jp074777r] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Adam W. Perriman
- Research School of Chemistry, Australian National University, Canberra ACT 0200, Australia, and ISIS, CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon UKO X110 QX
| | - Mark J. Henderson
- Research School of Chemistry, Australian National University, Canberra ACT 0200, Australia, and ISIS, CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon UKO X110 QX
| | - Stephen A. Holt
- Research School of Chemistry, Australian National University, Canberra ACT 0200, Australia, and ISIS, CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon UKO X110 QX
| | - John W. White
- Research School of Chemistry, Australian National University, Canberra ACT 0200, Australia, and ISIS, CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon UKO X110 QX
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Dar TA, Singh LR, Islam A, Anjum F, Moosavi-Movahedi AA, Ahmad F. Guanidinium chloride and urea denaturations of β-Lactoglobulin A at pH 2.0 and 25 °C: The equilibrium intermediate contains non-native structures (helix, tryptophan and hydrophobic patches). Biophys Chem 2007; 127:140-8. [PMID: 17289254 DOI: 10.1016/j.bpc.2007.01.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2006] [Revised: 01/19/2007] [Accepted: 01/21/2007] [Indexed: 11/24/2022]
Abstract
We have carried out guanidinium chloride (GdmCl) and urea denaturations of bovine beta-lactoglobulin A (beta-lgA) at pH 2.0 and 25 degrees C, using far-UV and near-UV circular dichroism, near-UV absorption and tryptophan fluorescence spectroscopies. The stable intermediate state that occurs during GdmCl denaturation has been characterized by the far- and near-UV circular dichroism, tryptophan difference absorption, tryptophan fluorescence and 8-anilino-1-naphthalene sulphonic acid binding measurements. Following conclusions have been reached. (a) Urea-induced denaturation is not a two-state process. (b) GdmCl-induced denaturation is composed of two distinct two-state processes. (c) alpha-Helical content, burial of tryptophan residues and burial of hydrophobic surface area are more in the GdmCl-induced stable intermediate than those originally present in the native protein.
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Affiliation(s)
- Tanveer Ali Dar
- Department of Biosciences, Centre for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, Jamia Nagar, New Delhi-110 025, India
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Romero CM, Lozano JM, Sancho J, Giraldo GI. Thermal stability of β-lactoglobulin in the presence of aqueous solution of alcohols and polyols. Int J Biol Macromol 2007; 40:423-8. [PMID: 17141862 DOI: 10.1016/j.ijbiomac.2006.10.003] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2006] [Revised: 10/23/2006] [Accepted: 10/26/2006] [Indexed: 11/19/2022]
Abstract
A systematic study concerning the effect of aqueous solution of alcohols and polyols with four carbon atoms on beta-lactoglobulin stability is presented. The protein was chosen due to its functional properties and applications in food and pharmaceutical industries and because its structure and properties in aqueous solution have been widely described. The alcohols having a four carbon chain were selected to examine the effect of the gradual increase in the number of OH groups on protein stability. Protein thermal stability in water, buffers and dilute aqueous solutions of 1-butanol, 1,2-butanediol, 1,2,4-butanetriol and 1,2,3,4-butanetetrol was evaluated by fluorescence spectroscopy. The results were used to determine the temperature range in which the unfolding process is reversible and the protein denaturation temperature in acetate buffer pH 5.5 and in the aqueous mixed solvents. Thermodynamic results show that alcohol denaturating effect diminishes gradually as the number of OH groups increase.
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Affiliation(s)
- Carmen M Romero
- Departamento de Química, Universidad Nacional de Colombia, Bogotá, Colombia.
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26
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Harvey BJ, Bell E, Brancaleon L. A Tryptophan Rotamer Located in a Polar Environment Probes pH-Dependent Conformational Changes in Bovine β-Lactoglobulin A. J Phys Chem B 2007; 111:2610-20. [PMID: 17300189 DOI: 10.1021/jp065783a] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Bovine beta-lactoglobulin A (BLGA) is a well characterized globular protein whose tertiary structure has been investigated in detail. BLGA undergoes a pH-dependent conformational change which X-ray data described as involving mostly the loop connecting strands E and F and the deprotonation of a glutamic acid residue (Glu89). These structural changes have been investigated using, among other techniques, fluorescence spectroscopy. The intrinsic fluorescence of BLGA is dominated by two Trp residues. These residues are located far from the EF loop and would not be expected to probe the pH-induced conformational change of the protein. Trp19 is located at the bottom of the interior beta-barrel, whereas Trp61 is located at the aperture of the barrel near the CD loop and is "silent" in the emission of native BLGA because of the proximity of a disulfide moiety. Our study suggests that, surprisingly, the fluorescence of Trp19 has the characteristic of a more polar environment than structural models from X-ray data would suggest and that at least two distinct conformations (or rotamers) of Trp19 contribute to the fluorescence of the protein. The less populated rotamer (relative amplitude (alpha) approximately 20%, tau approximately 3 ns) probes a more polar environment and a pH-dependent conformational change of BLGA in the region of Trp19 which X-ray data do not detect. Finally, our study provides the estimate of the fluorescence lifetime of Trp61 in the "unquenched" form.
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Affiliation(s)
- Billie J Harvey
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas, USA
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27
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Croguennec T, Renault A, Bouhallab S, Pezennec S. Interfacial and foaming properties of sulfydryl-modified bovine β-lactoglobulin. J Colloid Interface Sci 2006; 302:32-9. [PMID: 16876179 DOI: 10.1016/j.jcis.2006.06.061] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2006] [Revised: 06/16/2006] [Accepted: 06/17/2006] [Indexed: 10/24/2022]
Abstract
The effects of a control blocking of free cystein by N-ethylmaleimide on the interfacial behavior (kinetics of adsorption at the air/water interface, rheology of the interfacial layer) as well as on the foaming properties (density, stability) of beta-lactoglobulin were investigated. Compared to native beta-lactoglobulin (unmodified beta-lactoglobulin), sulfydryl-modified beta-lactoglobulin exhibited higher surface hydrophobicity, adsorbed faster at the air/water interface, had the capability to develop rapidly an interfacial layer with high shear elastic constant but exhibited a considerably lower shear elastic constant plateau value. Moreover, sulfydryl-modified beta-lactoglobulin exhibited better foaming properties especially regarding the short-term foam stability suggesting that the initial rheology of the interfacial film is at least as much important for the general mechanism of foam stabilization as the potential viscoelasticity the interfacial film could reach on aging.
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Affiliation(s)
- Thomas Croguennec
- UMR 1253 Science et Technologie du Lait et de l'Oeuf, INRA-Agrocampus Rennes, CS-84215, 65, rue de St. Brieuc, 35042 Rennes Cedex, France.
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28
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Bramanti E, Allegrini C, Onor M, Raspi G, Skogerboe KJ, Synovec RE. Flow injection analysis with diode array absorbance detection and dynamic surface tension detection for studying denaturation and surface activity of globular proteins. Anal Biochem 2006; 351:100-13. [PMID: 16438927 DOI: 10.1016/j.ab.2005.12.017] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2005] [Revised: 12/09/2005] [Accepted: 12/09/2005] [Indexed: 10/25/2022]
Abstract
In this article, a multidimensional dynamic surface tension detector (DSTD), in a parallel configuration with a UV-visible diode array absorbance detector, is presented in a novel flow injection analysis (FIA) application to study the effects of chemical denaturants urea, guanidinium hydrochloride (GdmHCl), and guanidinium thyocyanate (GdmSCN) on the surface activity of globular proteins at the liquid-air interface. The DSTD signal is obtained by measuring the changing pressure across the liquid-air interface of 4-mul drops repeatedly forming at the end of a capillary using FIA. The sensitivity and selectivity of the DSTD signal is related to the surface-active protein concentration in aqueous solution combined with the thermodynamics and kinetics of protein interaction at a liquid-air drop interface. Rapid on-line calibration and measurement of dynamic surface tension is applied, with the surface tension converted into surface pressure results. Continuous surface tension measurement throughout the entire drop growth is achieved, providing insight into kinetic behavior of protein interactive processes at the liquid-air drop interface. Specifically, chemical denaturation of 12 commercial globular proteins-chicken egg albumin, bovine serum albumin, human serum albumin, alpha-lactalbumin (alpha-Lac), myoglobin, cytochrome c, hemoglobin, carbonic anhydrase, alpha-chymotrypsinogen A, beta-lactoglobulin (beta-LG), lysozyme, and glyceraldehyde-3-phosphate-dehydrogenase-is studied in terms of surface pressure (i.e., surface activity) after treatment with increasing concentrations of urea, GdmHCl, and GdmSCN in the 0-8, 0-6, and 0-5 M ranges, respectively. For several of these proteins, the spectroscopic absorbance changes are monitored simultaneously to provide additional information prior to drop formation. Results show that surface pressure of proteins generally increases as the denaturant concentration increases and that effectiveness is GdmSCN > GdmHCl > urea. Protein unfolding curves obtained by plotting surface pressure as a function of denaturant concentration are presented and compared with respect to unfolding curves obtained by using UV absorbance and literature data. Kinetic information relative to the protein adsorption to the air-liquid interface of two proteins, alpha-Lac and beta-LG (chosen as representative proteins for comparison), denatured by the three denaturants is also studied and discussed.
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Affiliation(s)
- Emilia Bramanti
- CNR-Institute for Chemical and Physical Processes (IPCF), Laboratory of Instrumental Analytical Chemistry, 56124 Pisa, Italy.
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29
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Portugal CAM, Crespo JG, Lima JC. Anomalous “unquenching” of the fluorescence decay times of β-lactoglobulin induced by the known quencher acrylamide. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2006; 82:117-26. [PMID: 16288883 DOI: 10.1016/j.jphotobiol.2005.09.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2005] [Revised: 08/22/2005] [Accepted: 09/09/2005] [Indexed: 10/25/2022]
Abstract
Picosecond time-resolved fluorescence, together with the addition of quenching agents, was employed to discriminate the fluorescence contributions of the two tryptophans of beta-lactoglobulin (Trp19 and Trp61) to the fluorescence decays of the protein. The fluorescence decays of beta-lactoglobulin at pH 3, 5 and 8 are best fitted using sums of three exponentials and show a dominant contribution (98%) of the components associated with the buried Trp19, which decays according to a double exponential function. The addition of acrylamide (0.05 M) causes an increase of the decay times associated with Trp19. This effect is observed at all pH values studied, but the effect is stronger at pH 3 and pH 5, than at pH 8. The unexpected increase of the decay times of Trp19 and the variation of the respective amplitudes were rationalized in terms of alterations of Trp19 mobility. The hindrance of Trp19 upon acrylamide binding was also monitored and supported by fluorescence anisotropy measurements.
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Affiliation(s)
- Carla A M Portugal
- Requimte-CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Quinta da Torre, Monte da Caparica, 2825-516 Caparica, Portugal
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30
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Lee BK, Shimanouchi T, Umakoshi H, Kuboi R. Evaluation of carboxylic acid-induced conformational transitions of β-lactoglobulin: Comparison of the alcohol effects on β-lactoglobulin. Biochem Eng J 2006. [DOI: 10.1016/j.bej.2005.08.040] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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31
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van Teeffelen AMM, Meinders MBJ, de Jongh HHJ. Identification of pitfalls in the analysis of heat capacity changes of β-lactoglobulin A. Int J Biol Macromol 2005; 37:28-34. [PMID: 16197991 DOI: 10.1016/j.ijbiomac.2005.08.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2005] [Revised: 08/10/2005] [Accepted: 08/10/2005] [Indexed: 10/25/2022]
Abstract
Information on changes in heat capacity (DeltaCp) of proteins upon unfolding is used frequently in literature to understand possible follow-up reactions of protein denaturation, like their aggregation propensity. This thermodynamic property is intrinsic to the protein's architecture and unfolding and should be independent of the approach used to evaluate it. However, for many proteins, the reported values for DeltaCp vary considerably. To identify whether the origin of these discrepancies lies within the experimental approach chosen and/or in the too simplified unfolding models used in the analysis of the data, we choose beta-lactoglobulin A, a relatively small protein, but disputed for its two-state unfolding, and established its DeltaCp from tryptophan fluorescence, near-UV circular dichroism and differential scanning calorimetric measurements. In view of the large variation for the obtained DeltaCp (between 3.2 and 10.1+/-0.8 kJ/(mol K)), it is evident that: (1) the sensitivity of different approaches to the structural changes; (2) irreversibility of unfolding; (3) non-ideal two-state unfolding behaviour need to be considered prior to interpretation. While the first two points can be addressed by using multiple approaches, the applicability of the selected unfolding behaviour for the analysis is often less easy to establish. In this work, we illustrate that by checking the wavelength-dependence used to detect protein conformational changes a tool is provided that gives a direct insight in the validity of the interpretation in these studies. An experimentally validated determination of DeltaCp allows a more proper use for the mechanistic understanding of protein denaturation and its follow-up reactions, avoiding pitfalls in the interpretation.
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32
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Abstract
Why are there so many dimeric proteins and enzymes? While for heterodimers a functional explanation seems quite reasonable, the case of homodimers is more puzzling. The number of homodimers found in all living organisms is rapidly increasing. A thorough inspection of the structural data from the available literature and stability (measured from denaturation-renaturation experiments) allows one to suggest that homodimers can be divided into three main types according to their mass and the presence of a (relatively) stable monomeric intermediate in the folding-unfolding pathway. Among other explanations, we propose that an essential advantage for a protein being dimeric may be the proper and rapid assembly in the cellular milieu.
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Affiliation(s)
- Giampiero Mei
- Department of Experimental Medicine and Biochemical Sciences, University of Rome 'Tor Vergata', Rome, Italy.
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33
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Viseu MI, Carvalho TI, Costa SMB. Conformational transitions in beta-lactoglobulin induced by cationic amphiphiles: equilibrium studies. Biophys J 2004; 86:2392-402. [PMID: 15041677 PMCID: PMC1304088 DOI: 10.1016/s0006-3495(04)74296-4] [Citation(s) in RCA: 127] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
The conformational transition from the native state in water ("beta-state") to a state containing a considerable amount of alpha-helices ("alpha-state") was studied for the protein beta-lactoglobulin (BLG), from bovine milk, in several colloidal solutions containing mixed micelles or spontaneous vesicles. These aggregates were formed in the bicationic system containing the surfactant dodecyltrimethylammonium chloride (DTAC) and the lipid didodecyldimethylammonium bromide (DDAB). The beta-->alpha transition in BLG, investigated by far-ultraviolet circular dichroism spectroscopy, is induced to the same protein alpha-state by pure and mixed DDAB/DTAC micelles or vesicles. This implies a similar interaction mechanism of BLG with DDAB or DTAC, once the colloidal aggregates are formed. In premicelle DTAC solutions, the fraction of alpha-helix is lower and increases with the DTAC concentration. DDAB and DTAC also promote conformational changes in the protein tertiary structure that expose the tryptophans to a less constrained environment. These unfolding transitions were investigated by near-ultraviolet circular dichroism and steady-state fluorescence spectroscopies. In equilibrium conditions, it was found that higher DTAC (and, probably, DDAB) concentrations are needed to induce the beta-->alpha transition than to unfold the protein. beta-Lactoglobulin may therefore be considered as a model for protein-surfactant and protein-lipid interactions.
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Affiliation(s)
- Maria Isabel Viseu
- Centro de Química Estrutural, Instituto Superior Técnico, 1049-001 Lisbon, Portugal.
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34
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D'Alfonso L, Collini M, Ragona L, Ugolini R, Baldini G, Molinari H. Porcine beta-lactoglobulin chemical unfolding: Identification of a non-native α-helical intermediate. Proteins 2004; 58:70-9. [PMID: 15526300 DOI: 10.1002/prot.20309] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The chemical unfolding behavior of porcine beta-lactoglobulin (PLG) has been followed at pH 2 and 6 in the presence of guanidinium hydrochloride. The PLG unfolding transition, monitored by tryptophan fluorescence, far and near UV circular dichroism and 1D-NMR, can be described by a three-state transition suggesting the presence of at least one intermediate state that appears to display an excess of non-native alpha-helical structures. The thermodynamic parameters, as determined through a global analysis fitting procedure, give estimates of the free energy differences of the transitions connecting the native, the intermediate and the unfolded state: DeltaG(NI) (0) = 2.8 +/- 0.7 kcal mol(-1) (pH 2) and 4.2 +/- 0.5 kcal mol(-1) (pH 6) and DeltaG(NU) (0) = 7.2 +/- 0.6 kcal mol(-1) (pH 2) and 6.9 +/- 0.6 kcal mol(-1) (pH 6). CD unfolding data of the bovine species (BLG) have been collected here under the same experimental conditions of PLG to allow a careful comparison of the two beta-lactoglobulins. Intermediates with different characteristics have been identified for BLG and PLG, and their nature has been discussed on a structural analysis basis. The thermodynamic data reported here for PLG and BLG and the comparative analysis with data reported for equine beta lactoglobulin, show that homologous beta-barrel proteins, belonging to the same family and displaying high sequence identity (52-64%) populate unfolding intermediates to different extents, even though a common tendency to the formation of non-native alpha-helical intermediates, can be envisaged. The present results provide a prerequisite foundation of knowledge for the design and interpretation of future folding kinetic studies.
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Affiliation(s)
- Laura D'Alfonso
- Dipartimento di Fisica, Universitá degli Studi di Milano-Bicocca, Piazza della Scienza 3, 20126, Milano, Italy
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35
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Bouhallab S, Henry G, Caussin F, Croguennec T, Fauquant J, Mollé D. Copper-catalyzed formation of disulfide-linked dimer of bovineβ-lactoglobulin. ACTA ACUST UNITED AC 2004. [DOI: 10.1051/lait:2004023] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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36
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Parisi M, Mazzini A, Sorbi RT, Ramoni R, Grolli S, Favilla R. Unfolding and refolding of porcine odorant binding protein in guanidinium hydrochloride: equilibrium studies at neutral pH. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2003; 1652:115-25. [PMID: 14644047 DOI: 10.1016/j.bbapap.2003.08.009] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Unfolding and refolding studies on porcine odorant binding protein (pOBP) have been performed at pH 7 in the presence of guanidinium hydrochloride (GdnHCl). Unfolding, monitored by following changes of protein fluorescence and circular dichroism (CD), was found to be a reversible process, in terms of recovered structure and function. The equilibrium transition data were fitted by a simple two-state sigmoidal function of denaturant concentration and the thermodynamic folding parameters, derived from the two techniques, were very similar (average values: C(1/2) approximately 2.4 M, m approximately 2 kcal mol(-1) M(-1), DeltaG(unf,w)(0) approximately 4.7 kcal mol(-1)). The transition was independent of protein concentration, indicating that only monomeric species are involved. Only a minor protective effect by the fluorescent ligand 1-amino-anthracene (AMA) against protein unfolding was detected, whereas dihydromyrcenol (DHM) stabilised the protein to a larger extent (DeltaC(1/2) approximately 0.5 M). Refolding was complete, when the protein, denatured with GdnHCl, was diluted with buffer. On the other hand, refolding by dialysis was largely prevented by concomitant aggregation. The present results on pOBP are compared with those on bovine OBP (bOBP) [Biochim. Biophys. Acta 1599 (2002) 90], where subunit folding is accompanied by domain swapping. We finally suggest that the generally observed two-state folding of many lipocalins is probably favoured by their beta-barrel topology.
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Affiliation(s)
- Mariella Parisi
- Istituto Nazionale di Fisica della Materia (INFM), Unità di Parma, Università di Parma, Parma, Italy
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37
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Militello V, Vetri V, Leone M. Conformational changes involved in thermal aggregation processes of bovine serum albumin. Biophys Chem 2003; 105:133-41. [PMID: 12932585 DOI: 10.1016/s0301-4622(03)00153-4] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report a kinetic study on thermal aggregation process of the model protein bovine serum albumin (BSA) in low concentration regime. Aim of this study is to provide information on relationship between conformational changes and initial step of aggregation. The experimental approach is based on steady-state fluorescence spectra of the two tryptophans located in two different domains, in way to study conformational changes in the surrounding of these residues. We also follow emission spectra of Fluorescein-5-Maleimide dye bound to the single free cysteine of BSA. Complementary information on the extent of aggregation and on the structural changes is obtained by Rayleigh scattering and circular dichroism measurements. These data contribute to clarify the connection between conformational changes at tertiary and secondary structure level during the aggregation and how the different domains are involved. We also discuss the relevant role played by cysteine 34 in the aggregation pathways.
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Affiliation(s)
- Valeria Militello
- Istituto Nazionale per la Fisica della Materia and Department of Physical and Astronomical Sciences, University of Palermo, Palermo, Italy.
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38
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D'Alfonso L, Collini M, Baldini G. Trehalose influence on beta-lactoglobulin stability and hydration by time resolved fluorescence. EUROPEAN JOURNAL OF BIOCHEMISTRY 2003; 270:2497-504. [PMID: 12755705 DOI: 10.1046/j.1432-1033.2003.03621.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The stabilizing role of the disaccharide trehalose on beta-lactoglobulin (BLG) against its chemical denaturation both at native and acidic pH has been explored by means of time-resolved fluorescence of the probe acrylodan covalently bound to the unique free cysteine of BLG. The changes in acrylodan fluorescence lifetime with guanidinium chloride concentration reveal BLG sigmoidal denaturation profiles which depend upon the amount of trehalose in solution. When adding trehalose the transition midpoint shifts towards higher denaturant concentration. This effect has been measured by fitting the data with a two-state model whose parameters indicate that an almost 60% increase in the denaturation free energy is induced independently of trehalose concentrations and pH values. Fluorescence anisotropy measurements performed in the same conditions reveal that the internal dynamics are largely affected by the sugar, which makes the acrylodan environment more rigid, and by the denaturant that acts in the opposite way. The overall rotational diffusion of BLG suggests that trehalose affects the hydrodynamic properties of the solution in the proximity of the protein; tentative mechanisms are discussed.
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Affiliation(s)
- Laura D'Alfonso
- Dipartimento di Fisica, Università degli Studi di Milano-Bicocca, and Istituto Nazionale per la Fisica della Materia, Milano, Italy
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