1
|
Seelig J, Seelig A. Protein Stability─Analysis of Heat and Cold Denaturation without and with Unfolding Models. J Phys Chem B 2023; 127:3352-3363. [PMID: 37040567 PMCID: PMC10123674 DOI: 10.1021/acs.jpcb.3c00882] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/13/2023]
Abstract
Protein stability is important in many areas of life sciences. Thermal protein unfolding is investigated extensively with various spectroscopic techniques. The extraction of thermodynamic properties from these measurements requires the application of models. Differential scanning calorimetry (DSC) is less common, but is unique as it measures directly a thermodynamic property, that is, the heat capacity Cp(T). The analysis of Cp(T) is usually performed with the chemical equilibrium two-state model. This is not necessary and leads to incorrect thermodynamic consequences. Here we demonstrate a straightforward model-independent evaluation of heat capacity experiments in terms of protein unfolding enthalpy ΔH(T), entropy ΔS(T), and free energy ΔG(T)). This now allows the comparison of the experimental thermodynamic data with the predictions of different models. We critically examined the standard chemical equilibrium two-state model, which predicts a positive free energy for the native protein, and diverges distinctly from the experimental temperature profiles. We propose two new models which are equally applicable to spectroscopy and calorimetry. The ΘU(T)-weighted chemical equilibrium model and the statistical-mechanical two-state model provide excellent fits of the experimental data. They predict sigmoidal temperature profiles for enthalpy and entropy, and a trapezoidal temperature profile for the free energy. This is illustrated with experimental examples for heat and cold denaturation of lysozyme and β-lactoglobulin. We then show that the free energy is not a good criterion to judge protein stability. More useful parameters are discussed, including protein cooperativity. The new parameters are embedded in a well-defined thermodynamic context and are amenable to molecular dynamics calculations.
Collapse
Affiliation(s)
- Joachim Seelig
- Biozentrum, University of Basel, Spitalstrasse 41, CH-4056 Basel, Switzerland
| | - Anna Seelig
- Biozentrum, University of Basel, Spitalstrasse 41, CH-4056 Basel, Switzerland
| |
Collapse
|
2
|
Seelig J, Seelig A. Protein Unfolding-Thermodynamic Perspectives and Unfolding Models. Int J Mol Sci 2023; 24:5457. [PMID: 36982534 PMCID: PMC10049513 DOI: 10.3390/ijms24065457] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2022] [Revised: 02/06/2023] [Accepted: 02/09/2023] [Indexed: 03/14/2023] Open
Abstract
We review the key steps leading to an improved analysis of thermal protein unfolding. Thermal unfolding is a dynamic cooperative process with many short-lived intermediates. Protein unfolding has been measured by various spectroscopic techniques that reveal structural changes, and by differential scanning calorimetry (DSC) that provides the heat capacity change Cp(T). The corresponding temperature profiles of enthalpy ΔH(T), entropy ΔS(T), and free energy ΔG(T) have thus far been evaluated using a chemical equilibrium two-state model. Taking a different approach, we demonstrated that the temperature profiles of enthalpy ΔH(T), entropy ΔS(T), and free energy ΔG(T) can be obtained directly by a numerical integration of the heat capacity profile Cp(T). DSC thus offers the unique possibility to assess these parameters without resorting to a model. These experimental parameters now allow us to examine the predictions of different unfolding models. The standard two-state model fits the experimental heat capacity peak quite well. However, neither the enthalpy nor entropy profiles (predicted to be almost linear) are congruent with the measured sigmoidal temperature profiles, nor is the parabolic free energy profile congruent with the experimentally observed trapezoidal temperature profile. We introduce three new models, an empirical two-state model, a statistical-mechanical two-state model and a cooperative statistical-mechanical multistate model. The empirical model partially corrects for the deficits of the standard model. However, only the two statistical-mechanical models are thermodynamically consistent. The two-state models yield good fits for the enthalpy, entropy and free energy of unfolding of small proteins. The cooperative statistical-mechanical multistate model yields perfect fits, even for the unfolding of large proteins such as antibodies.
Collapse
Affiliation(s)
- Joachim Seelig
- Biozentrum, University of Basel, Spitalstrasse 41, CH-4056 Basel, Switzerland
| | | |
Collapse
|
3
|
Seelig J, Seelig A. Molecular understanding of calorimetric protein unfolding experiments. BIOPHYSICAL REPORTS 2022; 2:100037. [PMID: 36425081 PMCID: PMC9680786 DOI: 10.1016/j.bpr.2021.100037] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/09/2021] [Accepted: 12/02/2021] [Indexed: 06/16/2023]
Abstract
Testing and predicting protein stability gained importance because proteins, including antibodies, became pharmacologically relevant in viral and cancer therapies. Isothermal scanning calorimetry is the principle method to study protein stability. Here, we use the excellent experimental heat capacity Cp(T) data from the literature for a critical inspection of protein unfolding as well as for the test of a new cooperative model. In the relevant literature, experimental temperature profiles of enthalpy, Hcal(T), entropy, Scal(T), and free energy, Gcal(T) are missing. First, we therefore calculate the experimental Hcal(T), Scal(T), and Gcal(T) from published Cp(T) thermograms. Considering only the unfolding transition proper, the heat capacity and all thermodynamic functions are zero in the region of the native protein. In particular, the free energy of the folded proteins is also zero and Gcal(T) displays a trapezoidal temperature profile when cold denaturation is included. Second, we simulate the DSC-measured thermodynamic properties with a new molecular model based on statistical-mechanical thermodynamics. The model quantifies the protein cooperativity and predicts the aggregate thermodynamic variables of the system with molecular parameters only. The new model provides a perfect simulation of all thermodynamic properties, including the observed trapezoidal Gcal(T) temperature profile. Importantly, the new cooperative model can be applied to a broad range of protein sizes, including antibodies. It predicts not only heat and cold denaturation but also provides estimates of the unfolding kinetics and allows a comparison with molecular dynamics calculations and quasielastic neutron scattering experiments.
Collapse
Affiliation(s)
| | - Anna Seelig
- Biozentrum, University of Basel, Basel, Switzerland
| |
Collapse
|
4
|
Alexander Harrison J, Pruška A, Oganesyan I, Bittner P, Zenobi R. Temperature-Controlled Electrospray Ionization: Recent Progress and Applications. Chemistry 2021; 27:18015-18028. [PMID: 34632657 PMCID: PMC9298390 DOI: 10.1002/chem.202102474] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2021] [Indexed: 11/11/2022]
Abstract
Native electrospray ionization (ESI) and nanoelectrospray ionization (nESI) allow researchers to analyze intact biomolecules and their complexes by mass spectrometry (MS). The data acquired using these soft ionization techniques provide a snapshot of a given biomolecules structure in solution. Over the last thirty years, several nESI and ESI sources capable of controlling spray solution temperature have been developed. These sources can be used to elucidate the thermodynamics of a given analyte, as well as provide structural information that cannot be readily obtained by other, more commonly used techniques. This review highlights how the field of temperature-controlled mass spectrometry has developed.
Collapse
Affiliation(s)
| | - Adam Pruška
- Department of Chemistry and Applied BiosciencesETH ZurichVladimir-Prelog-Weg 38093ZurichSwitzerland
| | - Irina Oganesyan
- Department of Chemistry and Applied BiosciencesETH ZurichVladimir-Prelog-Weg 38093ZurichSwitzerland
| | - Philipp Bittner
- Department of Chemistry and Applied BiosciencesETH ZurichVladimir-Prelog-Weg 38093ZurichSwitzerland
| | - Renato Zenobi
- Department of Chemistry and Applied BiosciencesETH ZurichVladimir-Prelog-Weg 38093ZurichSwitzerland
| |
Collapse
|
5
|
Han R, Shi R, Yu Z, Ho H, Du Q, Sun X, Wang J, Jiang H, Fan R, Yang Y. Distribution and variation in proteins of casein micellar fractions response to heat-treatment from five dairy species. Food Chem 2021; 365:130640. [PMID: 34329874 DOI: 10.1016/j.foodchem.2021.130640] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Revised: 06/02/2021] [Accepted: 07/17/2021] [Indexed: 02/04/2023]
Abstract
Casein micelles (CMs) contribute to the physicochemical properties and stability of milk. However, how the proteome of CMs changes following heat treatment has not been elucidated. Here, changes in the proteins of CMs in samples of Holstein, buffalo, yak, goat, and camel milk following heat treatment were investigated using a LC-MS/MS approach. According to the hierarchical clustering results, Holstein, yak, and buffalo milk samples had similar CMs protein components, followed by goat and camel milk samples. Changes in lipoprotein lipase and α-lactalbumin in CMs were dependent on the intensity of heat treatment and were similar among the studied species, whereas changes in κ-casein, lactoferrin, and apolipoprotein A-I differed among different types of milk. These results provide information on the distribution and variations of the proteomes of CMs following heat treatment, which will assist in the identification of proteins that are dissociated and attached to CMs from different dairy species during heat treatment.
Collapse
Affiliation(s)
- Rongwei Han
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
| | - Runjia Shi
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
| | - Zhongna Yu
- Haidu College.Qingdao Agricultural University, Laiyang 265200, Shandong, China.
| | - Harvey Ho
- Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand.
| | - Qijing Du
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
| | - Xueheng Sun
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
| | - Jun Wang
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
| | - Hongning Jiang
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
| | - Rongbo Fan
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
| | - Yongxin Yang
- College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, Shandong, China.
| |
Collapse
|
6
|
Tárraga WA, Falomir-Lockhart LJ, Garda HA, González MC. Analysis of pyrene-labelled apolipoprotein A-I oligomerization in solution: Spectra deconvolution and changes in P-value and excimer formation. Arch Biochem Biophys 2021; 699:108748. [PMID: 33444627 DOI: 10.1016/j.abb.2020.108748] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Revised: 12/22/2020] [Accepted: 12/28/2020] [Indexed: 11/15/2022]
Abstract
ApoA-I is the main protein of HDL which has anti-atherogenic properties attributed to reverse cholesterol transport. It shares with other exchangeable apolipoproteins a high level of structural plasticity. In the lipid-free state, the apolipoprotein amphipathic α-helices interact intra- and inter-molecularly, providing structural stabilization by a complex self-association mechanism. In this study, we employed a multi-parametric fluorescent probe to study the self-association of apoA-I. We constructed six single cysteine mutants spanning positions along three helices: F104C, K107C (H4), K133C, L137C (H5), F225C and K226C (H10); and labelled them with N-Maleimide Pyrene. Taking advantage of its spectral properties, namely formation of an excited dimer (excimer) and polarity-dependent changes in its fluorescence fine structure (P-value), we monitored the apoA-I self-association in its lipid-free form as a function of its concentration. Interactions in helices H5 (K133C) and H10 (F225C and K226C) were highlighted by excimer emission; while polarity changes were reported in helix H4 (K107C), as well as in helices H5 and H10. Mathematical models were developed to enrich data analysis and estimate association constants (KA) and oligomeric species distribution. Furthermore, we briefly discuss the usefulness of the multi-parametric fluorescent probe to monitor different equilibria, even at a single labelling position. Results suggest that apoA-I self-association must be considered to fully understand its physiological roles. Particularly, some contacts that stabilize discoidal HDL particles seem to be already present in the lipid-free apoA-I oligomers.
Collapse
Affiliation(s)
- Wilson A Tárraga
- Instituto de Investigaciones Bioquímica de La Plata (INIBIOLP), Centro Científico Tecnológico-La Plata, Calle 60 y 120 s/n, 1900, La Plata, Argentina.
| | - Lisandro J Falomir-Lockhart
- Instituto de Investigaciones Bioquímica de La Plata (INIBIOLP), Centro Científico Tecnológico-La Plata, Calle 60 y 120 s/n, 1900, La Plata, Argentina; Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Calle 47 y 115 s/n, 1900, La Plata, Argentina.
| | - Horacio A Garda
- Instituto de Investigaciones Bioquímica de La Plata (INIBIOLP), Centro Científico Tecnológico-La Plata, Calle 60 y 120 s/n, 1900, La Plata, Argentina; Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Calle 60 y 120 s/n, 1900, La Plata, Argentina.
| | - Marina C González
- Instituto de Investigaciones Bioquímica de La Plata (INIBIOLP), Centro Científico Tecnológico-La Plata, Calle 60 y 120 s/n, 1900, La Plata, Argentina; Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Calle 60 y 120 s/n, 1900, La Plata, Argentina.
| |
Collapse
|
7
|
Garidel P, Eiperle A, Blech M, Seelig J. Thermal and Chemical Unfolding of a Monoclonal IgG1 Antibody: Application of the Multistate Zimm-Bragg Theory. Biophys J 2020; 118:1067-1075. [PMID: 32049058 PMCID: PMC7063443 DOI: 10.1016/j.bpj.2019.12.037] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Revised: 12/20/2019] [Accepted: 12/30/2019] [Indexed: 11/25/2022] Open
Abstract
The thermal unfolding of a recombinant monoclonal antibody IgG1 (mAb) was measured with differential scanning calorimetry (DSC). The DSC thermograms reveal a pretransition at 72°C with an unfolding enthalpy of ΔHcal ∼200-300 kcal/mol and a main transition at 85°C with an enthalpy of ∼900-1000 kcal/mol. In contrast to small single-domain proteins, mAb unfolding is a complex reaction that is analyzed with the multistate Zimm-Bragg theory. For the investigated mAb, unfolding is characterized by a cooperativity parameter σ ∼6 × 10-5 and a Gibbs free energy of unfolding of gnu ∼100 cal/mol per amino acid. The enthalpy of unfolding provides the number of amino acid residues ν participating in the unfolding reaction. On average, ν∼220 ± 50 amino acids are involved in the pretransition and ν∼850 ± 30 in the main transition, accounting for ∼90% of all amino acids. Thermal unfolding was further studied in the presence of guanidineHCl. The chemical denaturant reduces the unfolding enthalpy ΔHcal and lowers the midpoint temperature Tm. Both parameters depend linearly on the concentration of denaturant. The guanidineHCl concentrations needed to unfold mAb at 25°C are predicted to be 2-3 M for the pretransition and 5-7 M for the main transition, varying with pH. GuanidineHCl binds to mAb with an exothermic binding enthalpy, which partially compensates the endothermic mAb unfolding enthalpy. The number of guanidineHCl molecules bound upon unfolding is deduced from the DSC thermograms. The bound guanidineHCl-to-unfolded amino acid ratio is 0.79 for the pretransition and 0.55 for the main transition. The pretransition binds more denaturant molecules and is more sensitive to unfolding than the main transition. The current study shows the strength of the Zimm-Bragg theory for the quantitative description of unfolding events of large, therapeutic proteins, such as a monoclonal antibody.
Collapse
Affiliation(s)
- Patrick Garidel
- Boehringer Ingelheim Pharma GmbH & Co. KG, Innovation Unit, PDB, Biberach an der Riss, Germany.
| | - Andrea Eiperle
- Boehringer Ingelheim Pharma GmbH & Co. KG, Innovation Unit, PDB, Biberach an der Riss, Germany
| | - Michaela Blech
- Boehringer Ingelheim Pharma GmbH & Co. KG, Innovation Unit, PDB, Biberach an der Riss, Germany
| | - Joachim Seelig
- Biozentrum, University of Basel, Klingelbergstrasse 50/70, Basel, Switzerland.
| |
Collapse
|
8
|
Li-Blatter X, Seelig J. Thermal and Chemical Unfolding of Lysozyme. Multistate Zimm-Bragg Theory Versus Two-State Model. J Phys Chem B 2019; 123:10181-10191. [PMID: 31686511 DOI: 10.1021/acs.jpcb.9b08816] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Thermal and chemical unfolding of lysozyme in the presence of the guanidine HCl denaturant is a model system to compare the conventional two-state model of protein unfolding with the multistate Zimm-Bragg theory. The two-state model is shown to be the noncooperative limit of the Zimm-Bragg theory. In particular, the Zimm-Bragg theory provides a molecular interpretation of the empirical linear extrapolation method (LEM) of the two-state model. Differential scanning calorimetry (DSC) experiments reported in the literature are analyzed with both methods. Lysozyme unfolding is associated with a large endothermic enthalpy that decreases significantly upon addition of guanidine HCl. In contrast, the Gibbs free energy of unfolding is small, negative, and independent of the guanidine HCl concentration, contradicting, in part, the conclusions of the LEM. The unfolding enthalpy is compensated by an even larger entropy term. The multistate Zimm-Bragg theory predicts a larger conformational enthalpy and a smaller Gibbs free energy than the two-state model. The Zimm-Bragg theory provides the protein cooperativity parameter, the average length of independently folding protein domains, and the Gibbs free energy of unfolding of individual amino acid residues. Guanidine HCl binding to lysozyme is exothermic and counteracts the endothermic unfolding enthalpy. The number of bound denaturant molecules is determined from the decrease in enthalpy and is extrapolated to the guanidine HCl-to-amino acid stoichiometry at complete lysozyme unfolding. Chemical unfolding isotherms measured with circular dichroism (CD) spectroscopy are analyzed with both models. The chemical Zimm-Bragg theory is a cooperative molecular model, yielding the guanidine HCl binding constant and the protein cooperativity parameter. It allows a quantitative comparison between thermal and chemical protein unfolding. The two reactions have almost identical changes in Gibbs free energy. However, thermal unfolding is significantly more cooperative than chemical unfolding. Finally, distinct differences are observed in thermal unfolding between DSC and CD spectroscopy.
Collapse
Affiliation(s)
- Xiaochun Li-Blatter
- Biozentrum , University of Basel , Klingelbergstrasse 50/70 , CH-4056 Basel , Switzerland
| | - Joachim Seelig
- Biozentrum , University of Basel , Klingelbergstrasse 50/70 , CH-4056 Basel , Switzerland
| |
Collapse
|
9
|
Ma Y, Zhang L, Wu Y, Zhou P. Changes in milk fat globule membrane proteome after pasteurization in human, bovine and caprine species. Food Chem 2019; 279:209-215. [DOI: 10.1016/j.foodchem.2018.12.015] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Revised: 11/30/2018] [Accepted: 12/03/2018] [Indexed: 02/07/2023]
|
10
|
Eckhardt D, Li-Blatter X, Schönfeld HJ, Heerklotz H, Seelig J. Cooperative unfolding of apolipoprotein A-1 induced by chemical denaturation. Biophys Chem 2018; 240:42-49. [DOI: 10.1016/j.bpc.2018.05.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Revised: 05/22/2018] [Accepted: 05/22/2018] [Indexed: 12/30/2022]
|
11
|
Seelig J. Cooperative protein unfolding. A statistical-mechanical model for the action of denaturants. Biophys Chem 2017; 233:19-25. [PMID: 29232602 DOI: 10.1016/j.bpc.2017.12.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2017] [Revised: 11/30/2017] [Accepted: 12/02/2017] [Indexed: 01/09/2023]
Abstract
Knowledge of protein stability is of utmost importance in various fields of biotechnology. Protein stability can be assessed in solution by increasing the concentration of denaturant and recording the structural changes with spectroscopic or thermodynamic methods. The standard interpretation of the experimental data is to assume a 2-state equilibrium between completely folded and completely unfolded protein molecules. Here we propose a cooperative model based on the statistical-mechanical Zimm-Bragg theory. In this model protein unfolding is driven by the weak binding of a rather small number of denaturant molecules, inducing the cooperative unfolding with multiple dynamic intermediates. The modified Zimm-Bragg theory is applied to published thermodynamic and spectroscopic data leading to the following conclusions. (i) The binding constant KD is correlated with the midpoint concentration, c0, of the unfolding reaction according to c0≅1/KD. The better the binding of denaturant the lower is the concentration to achieve unfolding. (ii) The binding constant KD agrees with direct thermodynamic measurements. A rather small number of bound denaturants suffices to induce the cooperative unfolding of the whole protein. (iii) Chemical unfolding occurs in the concentration range ΔcD=cend-cini. The theory predicts the unfolding energy per amino acid residue as gnu=RTKD(cend-cini). The Gibbs free energy of an osmotic gradient of the same size is ΔGDiff=-RTln(cend/cini). In all examples investigated ΔGDiff exactly balances the unfolding energy gnu. The total unfolding energy is thus close to zero. (iv) Protein cooperativity in chemical unfolding is rather low with cooperativity parameters σ≥3x10-3. As a consequence, the theory predicts a dynamic mixture of conformations during the unfolding reaction. The probabilities of individual conformations are easily accessible via the partition function Z(cD,σ).
Collapse
Affiliation(s)
- J Seelig
- Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.
| |
Collapse
|
12
|
Mirheydari M, Mann EK, Kooijman EE. Interaction of a model apolipoprotein, apoLp-III, with an oil-phospholipid interface. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1860:396-406. [PMID: 29030246 DOI: 10.1016/j.bbamem.2017.10.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Revised: 09/22/2017] [Accepted: 10/08/2017] [Indexed: 01/29/2023]
Abstract
Lipid droplets are "small" organelles that play an important role in de novo synthesis of new membrane, and steroid hormones, as well as in energy storage. The way proteins interact specifically with the oil-(phospho-)lipid monolayer interface of lipid droplets is a relatively unexplored but crucial question. Here, we use our home built liquid droplet tensiometer to mimic intracellular lipid droplets and study protein-lipid interactions at this interface. As model neutral lipid binding protein, we use apoLp-III, an amphipathic α-helix bundle protein. This domain is also found in proteins from the perilipin family and in apoE. Protein binding to the monolayer is studied by the decrease in the oil/water surface tension. Previous work used POPC (one of the major lipids found on lipid droplets) to form the phospholipid monolayer on the triolein surface. Here we expand this work by incorporating other lipids with different physico-chemical properties to study the effect of charge and lipid head-group size. This study sheds light on the affinity of this important protein domain to interact with lipids.
Collapse
Affiliation(s)
- Mona Mirheydari
- Physics Department, Kent State University, Kent, OH 44242, United States.
| | - Elizabeth K Mann
- Physics Department, Kent State University, Kent, OH 44242, United States
| | - Edgar E Kooijman
- Department of Biological Sciences, Kent State University, Kent, OH 44242, United States
| |
Collapse
|
13
|
Rodríguez Nassif A, de la Arada I, Arrondo JL, Pastrana-Rios B. 2D IR Correlation Spectroscopy in the Determination of Aggregation and Stability of KH Domain GXXG Loop Peptide in the Presence and Absence of Trifluoroacetate. Anal Chem 2017; 89:5765-5775. [PMID: 28459550 DOI: 10.1021/acs.analchem.6b04800] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Trifluoroacetate (TFA) is a strong anion byproduct of solid-phase peptide synthesis. Fourier transform infrared (FT-IR) spectroscopy can be used to ascertain the presence of this excipient in peptide samples for quality assessment. TFA absorbs as a strong sharp peak (1675 cm-1) within the amide I' band of the spectral region. A peptide sample and the TFA excipient can be studied simultaneously by FT-IR and 2D IR correlation spectroscopies. In addition, these techniques are able to determine the effect of TFA on the stability of the peptide. Herein, we describe the spectroscopic characterization of the GXXG loop peptide (GXXGlp), which is present in KH domain containing proteins. The sequence of the Homo sapiens Krr1 GXXGlp is evolutionarily conserved (165KRRQRLIGPKGSTLKALELLTNCY189) and has been associated with ssDNA interaction and ribosome biogenesis. Our goal was to determine the structural elements present in this peptide and evaluate whether TFA affects the stability of GXXGlp during thermal stress. We observed differences in the molecular behavior of the synthetic peptide in the presence and absence of TFA at various peptide concentrations. Finally, 2D IR correlation spectroscopy was used for the determination of the unfolding process, mechanism and extent of peptide aggregation, and the effect of TFA on the stability of the peptide. This spectroscopic method can be applied to the characterization of any synthetic peptide.
Collapse
Affiliation(s)
- Aslin Rodríguez Nassif
- Department of Chemistry, University of Puerto Rico , Mayagüez Campus, Mayagüez, Puerto Rico 00681-9019, United States
| | - Igor de la Arada
- Biofisika Institute and Biochemistry and Molecular Biology Department, CSIC and University of Basque Country , Bilbao, 48080, Spain
| | - José Luis Arrondo
- Biofisika Institute and Biochemistry and Molecular Biology Department, CSIC and University of Basque Country , Bilbao, 48080, Spain
| | - Belinda Pastrana-Rios
- Department of Chemistry, University of Puerto Rico , Mayagüez Campus, Mayagüez, Puerto Rico 00681-9019, United States.,Protein Research Center, University of Puerto Rico , Mayagüez Campus, Mayagüez, Puerto Rico 00681-9019, United States
| |
Collapse
|
14
|
Thermal protein unfolding by differential scanning calorimetry and circular dichroism spectroscopy Two-state model versus sequential unfolding. Q Rev Biophys 2016; 49:e9. [PMID: 27658613 DOI: 10.1017/s0033583516000044] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Thermally-induced protein unfolding is commonly described with the two-state model. This model assumes only two types of protein molecules in solution, the native (N) and the denatured, unfolded (U) protein. In reality, protein unfolding is a multistep process, even if intermediate states are only sparsely populated. As an alternative approach we explore the Zimm-Bragg theory, originally developed for the α-helix-to-random coil transition of synthetic polypeptides. The theory includes intermediate structures with concentrations determined by the cooperativity of the unfolding reaction. We illustrate the differences between the two-state model and the Zimm-Bragg theory with measurements of apolipoprotein A-1 and lysozyme by differential scanning calorimetry (DSC) and CD spectroscopy. Nine further protein examples are taken from the literature. The Zimm-Bragg theory provides a perfect fit of the calorimetric unfolding transitions for all proteins investigated. In contrast, the transition curves and enthalpies predicted by the two-state model differ considerably from the experimental results. Apolipoprotein A-1 is ~50% α-helical at ambient temperature and its unfolding follows the classical α-helix-to-random coil equilibrium. The unfolding of proteins with little α-helix content, such as lysozyme, can also be analyzed with the Zimm-Bragg theory by introducing the concept of 'folded' and 'unfolded' peptide units assuming an average unfolding enthalpy per peptide unit. DSC is the method of choice to measure the unfolding enthalpy, , but CD spectroscopy in combination with the two-state model is often used to deduce the unfolding enthalpy. This can lead to erroneous result. Not only are different enthalpies required to describe the CD and DSC transition curves but these values deviate distinctly from the experimental result. In contrast, the Zimm-Bragg theory predicts the DSC and CD unfolding transitions with the same set of parameters.
Collapse
|
15
|
Schönfeld HJ, Roessner D, Seelig J. Self-Association of Apo A-1 Studied with Dynamic and Static Light Scattering. J Phys Chem B 2016; 120:1228-35. [DOI: 10.1021/acs.jpcb.5b12397] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
| | - Dierk Roessner
- Wyatt Technology Europe GmbH, Hochstraße 12a, DE-56307 Dernbach, Germany
| | - Joachim Seelig
- Biozentrum, University of Basel, Klingelbergstrasse 50/70, CH-4056 Basel, Switzerland
| |
Collapse
|
16
|
|
17
|
Angarita M, Arosio P, Müller-Späth T, Baur D, Falkenstein R, Kuhne W, Morbidelli M. Role of urea on recombinant Apo A-I stability and its utilization in anion exchange chromatography. J Chromatogr A 2014; 1354:18-25. [DOI: 10.1016/j.chroma.2014.05.067] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2014] [Revised: 05/23/2014] [Accepted: 05/27/2014] [Indexed: 10/25/2022]
|
18
|
Petrlova J, Dalla-Riva J, Mörgelin M, Lindahl M, Krupinska E, Stenkula KG, Voss JC, Lagerstedt JO. Secondary structure changes in ApoA-I Milano (R173C) are not accompanied by a decrease in protein stability or solubility. PLoS One 2014; 9:e96150. [PMID: 24755625 PMCID: PMC3995965 DOI: 10.1371/journal.pone.0096150] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2013] [Accepted: 04/04/2014] [Indexed: 11/29/2022] Open
Abstract
Apolipoprotein A-I (apoA-I) is the main protein of high-density lipoprotein (HDL) and a principal mediator of the reverse cholesterol transfer pathway. Variants of apoA-I have been shown to be associated with hereditary amyloidosis. We previously characterized the G26R and L178H variants that both possess decreased stability and increased fibril formation propensity. Here we investigate the Milano variant of apoAI (R173C; apoAI-M), which despite association with low plasma levels of HDL leads to low prevalence of cardiovascular disease in carriers of this mutation. The R173C substitution is located to a region (residues 170 to 178) that contains several fibrillogenic apoA-I variants, including the L178H variant, and therefore we investigated a potential fibrillogenic property of the apoAI-M protein. Despite the fact that apoAI-M shared several features with the L178H variant regarding increased helical content and low degree of ThT binding during prolonged incubation in physiological buffer, our electron microscopy analysis revealed no formation of fibrils. These results suggest that mutations inducing secondary structural changes may be beneficial in cases where fibril formation does not occur.
Collapse
Affiliation(s)
- Jitka Petrlova
- Department of Experimental Medical Science, Lund University, Lund, Sweden
| | | | | | - Maria Lindahl
- Department of Experimental Medical Science, Lund University, Lund, Sweden
| | - Ewa Krupinska
- Department of Experimental Medical Science, Lund University, Lund, Sweden
| | - Karin G. Stenkula
- Department of Experimental Medical Science, Lund University, Lund, Sweden
| | - John C. Voss
- School of Medicine, University of California Davis, Davis, California, United States of America
| | - Jens O. Lagerstedt
- Department of Experimental Medical Science, Lund University, Lund, Sweden
- * E-mail:
| |
Collapse
|
19
|
Arouri A, Dathe M, Blume A. The helical propensity of KLA amphipathic peptides enhances their binding to gel-state lipid membranes. Biophys Chem 2013; 180-181:10-21. [DOI: 10.1016/j.bpc.2013.05.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2013] [Revised: 05/17/2013] [Accepted: 05/18/2013] [Indexed: 12/18/2022]
|
20
|
Turcu I, Mic M. Size Dependence of Molecular Self-Assembling in Stacked Aggregates. 2. Heat Exchange Effects. J Phys Chem B 2013; 117:9083-93. [DOI: 10.1021/jp403768x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ioan Turcu
- Department of Molecular and Biomolecular Physics, National Institute of Isotopic and Molecular Technology, 400293 Cluj-Napoca, Romania
| | - Mihaela Mic
- Department of Molecular and Biomolecular Physics, National Institute of Isotopic and Molecular Technology, 400293 Cluj-Napoca, Romania
| |
Collapse
|
21
|
Wong YQ, Binger KJ, Howlett GJ, Griffin MD. Identification of an amyloid fibril forming peptide comprising residues 46-59 of apolipoprotein A-I. FEBS Lett 2012; 586:1754-8. [DOI: 10.1016/j.febslet.2012.05.007] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Revised: 05/02/2012] [Accepted: 05/03/2012] [Indexed: 11/28/2022]
|