1
|
Oliva R, Winter R. Harnessing Pressure-Axis Experiments to Explore Volume Fluctuations, Conformational Substates, and Solvation of Biomolecular Systems. J Phys Chem Lett 2022; 13:12099-12115. [PMID: 36546666 DOI: 10.1021/acs.jpclett.2c03186] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Intrinsic thermodynamic fluctuations within biomolecules are crucial for their function, and flexibility is one of the strategies that evolution has developed to adapt to extreme environments. In this regard, pressure perturbation is an important tool for mechanistically exploring the causes and effects of volume fluctuations in biomolecules and biomolecular assemblies, their role in biomolecular interactions and reactions, and how they are affected by the solvent properties. High hydrostatic pressure is also a key parameter in the context of deep-sea and subsurface biology and the study of the origin and physical limits of life. We discuss the role of pressure-axis experiments in revealing intrinsic structural fluctuations as well as high-energy conformational substates of proteins and other biomolecular systems that are important for their function and provide some illustrative examples. We show that the structural and dynamic information obtained from such pressure-axis studies improves our understanding of biomolecular function, disease, biological evolution, and adaptation.
Collapse
Affiliation(s)
- Rosario Oliva
- Department of Chemistry and Chemical Biology, Physical Chemistry I, Biophysical Chemistry, TU Dortmund University, Otto-Hahn-Strasse 6, Dortmund44227, Germany
- Department of Chemical Sciences, University of Naples Federico II, Via Cintia 4, 80126Naples, Italy
| | - Roland Winter
- Department of Chemistry and Chemical Biology, Physical Chemistry I, Biophysical Chemistry, TU Dortmund University, Otto-Hahn-Strasse 6, Dortmund44227, Germany
| |
Collapse
|
2
|
Jansens KJA, Brijs K, Stetefeld J, Delcour JA, Scanlon MG. Ultrasonic Characterization of Amyloid-Like Ovalbumin Aggregation. ACS OMEGA 2017; 2:4612-4620. [PMID: 31457750 PMCID: PMC6641891 DOI: 10.1021/acsomega.7b00366] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/28/2017] [Accepted: 06/29/2017] [Indexed: 06/10/2023]
Abstract
Thermal processing conditions, pH, and salt content affect the formation of egg white ovalbumin amyloid, which was investigated using high-precision measurements of ultrasonic velocity and attenuation. These were related to fluorescence and particle size measurements. Fluorescence changes indicated the formation of amyloid-like aggregates that was enhanced by increasing time-temperature treatments. The ultrasonic velocity of ovalbumin after heating at neutral pH (60 min at 70 or 80 °C) was lower than that of unheated ovalbumin, whereas the attenuation was higher. The decrease in the velocity represents increased compressibility associated with a change in the compactness of the protein, whereas changes in attenuation are due to protein conformational changes. Heating ramp studies revealed transitions at approximately 58 and 73 °C. During heating at a constant temperature, the ultrasonic velocity decreased slowly with increasing heating time, indicating an increase in ovalbumin compressibility. It is suggested that the obtained amyloid-like ovalbumin aggregates contain a compact core surrounded by loosely packed protein segments.
Collapse
Affiliation(s)
- Koen J. A. Jansens
- Laboratory
of Food Chemistry and Biochemistry, Leuven
Food Science and Nutrition Research Centre (LFoRCe), KU Leuven Kasteelpark Arenberg 20, B-3001 Leuven, Belgium
| | - Kristof Brijs
- Laboratory
of Food Chemistry and Biochemistry, Leuven
Food Science and Nutrition Research Centre (LFoRCe), KU Leuven Kasteelpark Arenberg 20, B-3001 Leuven, Belgium
| | - Jörg Stetefeld
- Department
of Chemistry, University of Manitoba, Winnipeg, Canada R2T 2N2
| | - Jan A. Delcour
- Laboratory
of Food Chemistry and Biochemistry, Leuven
Food Science and Nutrition Research Centre (LFoRCe), KU Leuven Kasteelpark Arenberg 20, B-3001 Leuven, Belgium
| | - Martin G. Scanlon
- Department
of Food Science, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2
| |
Collapse
|
3
|
Jansens KJ, Brijs K, Delcour JA, Scanlon MG. Amyloid-like aggregation of ovalbumin: Effect of disulfide reduction and other egg white proteins. Food Hydrocoll 2016. [DOI: 10.1016/j.foodhyd.2016.07.015] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
4
|
Ratha BN, Ghosh A, Brender JR, Gayen N, Ilyas H, Neeraja C, Das KP, Mandal AK, Bhunia A. Inhibition of Insulin Amyloid Fibrillation by a Novel Amphipathic Heptapeptide: MECHANISTIC DETAILS STUDIED BY SPECTROSCOPY IN COMBINATION WITH MICROSCOPY. J Biol Chem 2016; 291:23545-23556. [PMID: 27679488 PMCID: PMC5095409 DOI: 10.1074/jbc.m116.742460] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2016] [Revised: 09/24/2016] [Indexed: 02/02/2023] Open
Abstract
The aggregation of insulin into amyloid fibers has been a limiting factor in the development of fast acting insulin analogues, creating a demand for excipients that limit aggregation. Despite the potential demand, inhibitors specifically targeting insulin have been few in number. Here we report a non-toxic and serum stable-designed heptapeptide, KR7 (KPWWPRR-NH2), that differs significantly from the primarily hydrophobic sequences that have been previously used to interfere with insulin amyloid fibrillation. Thioflavin T fluorescence assays, circular dichroism spectroscopy, and one-dimensional proton NMR experiments suggest KR7 primarily targets the fiber elongation step with little effect on the early oligomerization steps in the lag time period. From confocal fluorescence and atomic force microscopy experiments, the net result appears to be the arrest of aggregation in an early, non-fibrillar aggregation stage. This mechanism is noticeably different from previous peptide-based inhibitors, which have primarily shifted the lag time with little effect on later stages of aggregation. As insulin is an important model system for understanding protein aggregation, the new peptide may be an important tool for understanding peptide-based inhibition of amyloid formation.
Collapse
Affiliation(s)
| | | | - Jeffrey R Brender
- Radiation Biology Branch, National Institutes of Health, Bethesda, Maryland 20814
| | - Nilanjan Gayen
- Department of Molecular Medicine, Bose Institute, P-1/12 CIT Scheme VII (M), Kolkata 700054, India
| | | | - Chilukoti Neeraja
- TIFR Centre for Interdisciplinary Sciences (TCIS), Narsingi, Hyderabad 500075, India, and
| | - Kali P Das
- Department of Chemistry, 93/1 APC Road, Bose Institute, Kolkata 700009, India
| | - Atin K Mandal
- Department of Molecular Medicine, Bose Institute, P-1/12 CIT Scheme VII (M), Kolkata 700054, India
| | | |
Collapse
|
5
|
Grasso E, Oliveira R, Maggio B. Surface interactions, thermodynamics and topography of binary monolayers of Insulin with dipalmitoylphosphatidylcholine and 1-palmitoyl-2-oleoylphosphatidylcholine at the air/water interface. J Colloid Interface Sci 2016; 464:264-76. [DOI: 10.1016/j.jcis.2015.11.034] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2015] [Revised: 11/15/2015] [Accepted: 11/17/2015] [Indexed: 11/30/2022]
|
6
|
Rao Jampani S, Mahmoudinobar F, Su Z, Dias CL. Thermodynamics of Aβ16-21 dissociation from a fibril: Enthalpy, entropy, and volumetric properties. Proteins 2015; 83:1963-72. [PMID: 26264694 DOI: 10.1002/prot.24875] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Revised: 07/22/2015] [Accepted: 08/02/2015] [Indexed: 11/10/2022]
Abstract
Here, we provide insights into the thermodynamic properties of A β16-21 dissociation from an amyloid fibril using all-atom molecular dynamics simulations in explicit water. An umbrella sampling protocol is used to compute potentials of mean force (PMF) as a function of the distance ξ between centers-of-mass of the A β16-21 peptide and the preformed fibril at nine temperatures. Changes in the enthalpy and the entropic energy are determined from the temperature dependence of these PMF(s) and the average volume of the simulation box is computed as a function of ξ. We find that the PMF at 310 K is dominated by enthalpy while the entropic energy does not change significantly during dissociation. The volume of the system decreases during dissociation. Moreover, the magnitude of this volume change also decreases with increasing temperature. By defining dock and lock states using the solvent accessible surface area (SASA), we find that the behavior of the electrostatic energy is different in these two states. It increases (unfavorable) and decreases (favorable) during dissociation in lock and dock states, respectively, while the energy due to Lennard-Jones interactions increases continuously in these states. Our simulations also highlight the importance of hydrophobic interactions in accounting for the stability of A β16-21.
Collapse
Affiliation(s)
- Srinivasa Rao Jampani
- Department of Physics, New Jersey Institute of Technology, Newark, New Jersey, 07102-1982
| | - Farbod Mahmoudinobar
- Department of Physics, New Jersey Institute of Technology, Newark, New Jersey, 07102-1982
| | - Zhaoqian Su
- Department of Physics, New Jersey Institute of Technology, Newark, New Jersey, 07102-1982
| | - Cristiano L Dias
- Department of Physics, New Jersey Institute of Technology, Newark, New Jersey, 07102-1982
| |
Collapse
|
7
|
Tachibana H. Basic Equations in Statics and Kinetics of Protein Polymerization and the Mechanism of the Formation and Dissociation of Amyloid Fibrils Revealed by Pressure Perturbation. Subcell Biochem 2015; 72:279-299. [PMID: 26174387 DOI: 10.1007/978-94-017-9918-8_14] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Studies of the pressure-dissociation of several amyloid or amyloid-like fibrils have shown that the fibril state is considerably voluminous. Quantitative characterization of the protein fibrillation reaction with respect to volumetric parameters is necessary to elucidate mechanisms of amyloid fibrillation in molecular terms such as protein cavity and hydration. Here we discuss, firstly, basic equations in statics and kinetics of protein polymerization as employed to obtain thermodynamic, volumetric, and kinetic parameters. Equilibrium treatment of the reactions with the scheme such as one-step polymerization, linear-association polymerization, or nucleation-dependent polymerization, and kinetic treatment of seeded linear-polymerization or spontaneous nucleation-elongation polymerization are described. In particular we will detail kinetics of the dissociation of fibrils which have been produced under the linear-association mechanism and therefore the length-distribution of which conforms to a geometric sequence in the degree of polymerization with a common ratio r, which is less than, and usually very close to, unity. In this case, an observed macroscopic rate of dissociation is shown to be a product of the microscopic elementary dissociation rate constant and a factor (1-r), extremely reduced compared with the intrinsic elementary rate. Secondly, we discuss protein conformational states in fibrillogenesis with molecular and volumetric observations reported, such as the unfolded state responsible for the association with seeds and the extension of amyloid fibrils, the transition state in which protein cavity formation and dehydration occur to intermediate levels, and the fibril state in which they occur to final respective levels which, in some cases, depend on the maturity of the fibril.
Collapse
Affiliation(s)
- Hideki Tachibana
- Department of Biotechnological Science, School of Biology-Oriented Science and Technology, and High Pressure Protein Research Center, Institute of Advanced Technology, Kinki University, 930 Nishimitani, Kinokawa, 649-6493, Japan,
| |
Collapse
|
8
|
Wawer J, Krakowiak J, Szociński M, Lustig Z, Olszewski M, Szostak K. Inhibition of amyloid fibril formation of hen egg white lysozyme by trimethylamine N-oxide at low pH. Int J Biol Macromol 2014; 70:214-21. [DOI: 10.1016/j.ijbiomac.2014.06.057] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Revised: 06/20/2014] [Accepted: 06/30/2014] [Indexed: 10/25/2022]
|
9
|
Babenko V, Piejko M, Wójcik S, Mak P, Dzwolak W. Vortex-induced amyloid superstructures of insulin and its component A and B chains. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:5271-5278. [PMID: 23590193 DOI: 10.1021/la400612w] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Insulin is an amyloid-forming polypeptide built of two disulfide-linked chains (A and B), both themselves amyloidogenic. An interesting property of insulin is that agitation strongly influences the course of its aggregation, resulting in characteristic chiral superstructures of amyloid fibrils. Here, we investigate the self-assembly of these superstructures by comparing the quiescent and vortex-assisted aggregation of insulin and its individual A and B chains in the presence or absence of reducing agent tris(2-carboxyethyl)phosphine (TCEP). Our study shows that only the B chain in the presence of TCEP is converted into aggregates with morphology (according to atomic force microscopy) and optical activity (manifested as an extrinsic Cotton effect induced in bound thioflavin T) characteristic of amyloid superstructures that are normally formed by insulin in the absence of TCEP. In contrast to more rigid B-peptide fibrils, elongated aggregates of the A peptide become amorphous upon agitation. Moreover, the aggregation of equimolar mixture of both peptides does not produce highly ordered entities. Our results suggest that the dynamics of the B chain are the driving force for the assembly of superstructures, with the A chain being complicit as long as its own dynamics are controlled by the firm attachment to the B chain provided by the intact covalent structure of insulin.
Collapse
Affiliation(s)
- Viktoria Babenko
- Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
| | | | | | | | | |
Collapse
|
10
|
Pfeiffer H, Chatziathanasiou N, Verstraeten B, Meersman F, Glorieux C, Heremans K, Wevers M. In-situ spectroscopic investigation of ultrasonic assisted unfolding and aggregation of insulin. BIOCHIMICA ET BIOPHYSICA ACTA 2013; 1834:336-341. [PMID: 22921831 DOI: 10.1016/j.bbapap.2012.08.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2012] [Revised: 07/24/2012] [Accepted: 08/04/2012] [Indexed: 06/01/2023]
Abstract
It is well-known that fibrillogenesis of proteins can be influenced by diverse external parameters, such as temperature, pressure, agitation or chemical agents. The present preliminary study suggests that ultrasonic excitation at moderate intensities has a significant influence on the unfolding and aggregation behaviour of insulin. Irradiation with an average sound intensity of even as low as 70mW/cm(2) leads to a lowering of the unfolding and aggregation temperature up to 7K. The effect could be explained by an increase of the aggregation kinetics due to ultrasonically induced acoustic micro-streaming in the insulin solution that most probably enhances the aggregation rate. The clear and remarkable effect at relatively low sound intensities offers interesting options for further applications of ultrasound in biophysics and biochemistry. On the other hand, a process that causes a change of kinetics equivalent to 7K also gives a warning signal concerning the safety of those medical ultrasonic devices that work in this intensity range.
Collapse
Affiliation(s)
- Helge Pfeiffer
- Department of Metallurgy and Materials Engineering, Group Material Performance and Non-destructive Testing, Katholieke Universiteit Leuven, Kasteelpark Arenberg 44, B-3001 Leuven, Belgium.
| | | | | | | | | | | | | |
Collapse
|
11
|
Liu W, Johnson S, Micic M, Orbulescu J, Whyte J, Garcia AR, Leblanc RM. Study of the aggregation of human insulin Langmuir monolayer. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:3369-3377. [PMID: 22263642 DOI: 10.1021/la204201w] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The human insulin (HI) Langmuir monolayer at the air-water interface was systematically investigated in the presence and absence of Zn(II) ions in the subphase. HI samples were dissolved in acidic (pH 2) and basic (pH 9) aqueous solutions and then spread at the air-water interface. Spectroscopic data of aqueous solutions of HI show a difference in HI conformation at different pH values. Moreover, the dynamics of the insulin protein showed a dependence on the concentration of Zn(II) ions. In the absence of Zn(II) ions in the subphase, the acidic and basic solutions showed similar behavior at the air-water interface. In the presence of Zn(II) ions in the subphase, the surface pressure-area and surface potential-area isotherms suggest that HI may aggregate at the air-water interface. It was observed that increasing the concentration of Zn(II) ions in the acidic (pH 2) aqueous solution of HI led to an increase of the area at a specific surface pressure. It was also seen that the conformation of HI in the basic (pH 9) medium had a reverse effect (decrease in the surface area) with the increase of the concentration of Zn(II) ions in solution. From the compression-decompression cycles we can conclude that the aggregated HI film at air-water interface is not stable and tends to restore a monolayer of monomers. These results were confirmed from UV-vis and fluorescence spectroscopy analysis. Infrared reflection-absorption and circular dichroism spectroscopy techniques were used to determine the secondary structure and orientation changes of HI by zinc ions. Generally, the aggregation process leads to a conformation change from α-helix to β-strand and β-turn, and at the air-water interface, the aggregation process was likewise seen to induce specific orientations for HI in the acidic and basic media. A proposed surface orientation model is presented here as an explanation to the experimental data, shedding light for further research on the behavior of insulin as a Langmuir monolayer.
Collapse
Affiliation(s)
- Wei Liu
- Department of Chemistry, University of Miami, 1301 Memorial Drive, Cox Science Center, Coral Gables, Florida 33146, USA
| | | | | | | | | | | | | |
Collapse
|
12
|
Pérez-López S, Blanco-Vila N, Vila-Romeu N. Bovine Insulin–Phosphatidylcholine Mixed Langmuir Monolayers: Behavior at the Air–Water Interface. J Phys Chem B 2011; 115:9387-94. [DOI: 10.1021/jp2033627] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- S. Pérez-López
- Department of Physical Chemistry-Faculty of Sciences in Ourense, University of Vigo; Campus As Lagoas s/n 32004 Ourense, Spain
| | - N.M. Blanco-Vila
- Department of Physical Chemistry-Faculty of Sciences in Ourense, University of Vigo; Campus As Lagoas s/n 32004 Ourense, Spain
| | - N. Vila-Romeu
- Department of Physical Chemistry-Faculty of Sciences in Ourense, University of Vigo; Campus As Lagoas s/n 32004 Ourense, Spain
| |
Collapse
|
13
|
Evers F, Steitz R, Tolan M, Czeslik C. Reduced protein adsorption by osmolytes. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2011; 27:6995-7001. [PMID: 21568286 DOI: 10.1021/la2010908] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Osmolytes are substances that affect osmosis and are used by cells to adapt to environmental stress. Here, we report a neutron reflectivity study on the influence of some osmolytes on protein adsorption at solid-liquid interfaces. Bovine ribonuclease A (RNase) and bovine insulin were used as model proteins adsorbing at a hydrophilic silica and at a hydrophobic polystyrene surface. From the neutron reflectivity data, the adsorbed protein layers were characterized in terms of layer thickness, protein packing density, and adsorbed protein mass in the absence and presence of urea, trehalose, sucrose, and glycerol. All data point to the clear effect of these nonionic cosolvents on the degree of protein adsorption. For example, 1 M sucrose leads to a reduction of the adsorbed amount of RNase by 39% on a silica surface and by 71% on a polystyrene surface. Trehalose was found to exhibit activity similar to that of sucrose. The changes in adsorbed protein mass can be attributed to a decreased packing density of the proteins in the adsorbed layers. Moreover, we investigated insulin adsorption at a hydrophobic surface in the absence and presence of glycerol. The degree of insulin adsorption is decreased by even 80% in the presence of 4 M of glycerol. The results of this study demonstrate that nonionic cosolvents can be used to tune and control nonspecific protein adsorption at aqueous-solid interfaces, which might be relevant for biomedical applications.
Collapse
Affiliation(s)
- Florian Evers
- Fakultät Chemie, Technische Universität Dortmund, D-44221 Dortmund, Germany
| | | | | | | |
Collapse
|
14
|
Fan HY, Nazari M, Chowdhury S, Heerklotz H. Volume and expansivity changes of micelle formation measured by pressure perturbation calorimetry. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2011; 27:1693-1699. [PMID: 21226468 DOI: 10.1021/la1042487] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We present the application of pressure perturbation calorimetry (PPC) as a new method for the volumetric characterization of the micelle formation of surfactants. The evaluation is realized by a global fit of PPC curves at different surfactant concentration ranging, if possible, from below to far above the CMC. It is based on the knowledge of the temperature dependence of the CMC, which can for example be characterized by isothermal titration calorimetry. We demonstrate the new approach for decyl-β-maltopyranoside (DM). It shows a strong volume increase upon micelle formation of 16 ± 2.5 mL/mol (+4%) at 25 °C, and changes with temperature by -0.1 mL/(mol K). The apparent molar expansivity (E(S)) decreases upon micelle formation from 0.44 to 0.31 mL/(mol K) at 25 °C. Surprisingly, the temperature dependence of the expansivity of DM in solution (as compared with that of maltose) does not agree with the principal behavior described for polar (E(S)(T) decreasing) and hydrophobic (E(S)(T) increasing) solutes or moieties before. The results are discussed in terms of changes in hydration of the molecules and internal packing of the micelles and compared with the volumetric effects of transitions of proteins, DNA, lipids, and polymers.
Collapse
Affiliation(s)
- Helen Y Fan
- Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College St., Toronto, ON M5S 3M2, Canada
| | | | | | | |
Collapse
|
15
|
|
16
|
Unraveling the Pressure Effect on Nucleation Processes of Amyloidogenic Proteins. Chemphyschem 2010; 11:2016-20. [DOI: 10.1002/cphc.202000074] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
|
17
|
Evers F, Reichhart C, Steitz R, Tolan M, Czeslik C. Probing adsorption and aggregation of insulin at a poly(acrylic acid) brush. Phys Chem Chem Phys 2010; 12:4375-82. [DOI: 10.1039/b925134k] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
18
|
Pressure dependence of the apparent specific volume of bovine serum albumin: Insight into the difference between isothermal and adiabatic compressibilities. Biophys Chem 2009; 144:67-71. [PMID: 19632757 DOI: 10.1016/j.bpc.2009.06.008] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2009] [Revised: 06/24/2009] [Accepted: 06/24/2009] [Indexed: 11/23/2022]
Abstract
There are some theoretical arguments related to interpreting the adiabatic compressibility (beta(s)) of a protein determined from the sound velocity and the difference between beta(s) and isothermal compressibility (beta(T)). To address these problems experimentally, we constructed a high-pressure oscillating densitometer and used it to measure the apparent specific volume of bovine serum albumin as a function of pressure (0.1-78MPa) and temperature (5-35 degrees C). The beta(T) determined from plots of the apparent specific volume vs. pressure was slightly larger than beta(s) at all temperatures examined, with the difference between the two compressibilities increasing as the temperature was decreased. Only at room temperature did the observed beta(T) agree with those estimated from beta(s) using the heat capacity and the thermal expansibility of the protein, suggesting that there are significant as-yet-unknown mechanisms that affect protein compressibility.
Collapse
|
19
|
Jeworrek C, Hollmann O, Steitz R, Winter R, Czeslik C. Interaction of IAPP and insulin with model interfaces studied using neutron reflectometry. Biophys J 2009; 96:1115-23. [PMID: 19186147 DOI: 10.1016/j.bpj.2008.11.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2008] [Accepted: 11/05/2008] [Indexed: 10/21/2022] Open
Abstract
The islet amyloid polypeptide (IAPP) and insulin are coproduced by the beta-cells of the pancreatic islets of Langerhans. Both peptides can interact with negatively charged lipid membranes. The positively charged islet amyloid polypeptide partially inserts into these membranes and subsequently forms amyloid fibrils. The amyloid fibril formation of insulin is also accelerated by the presence of negatively charged lipids, although insulin has a negative net charge at neutral pH-values. We used water-polymer model interfaces to differentiate between the hydrophobic and electrostatic interactions that can drive these peptides to adsorb at an interface. By applying neutron reflectometry, the scattering-length density profiles of IAPP and insulin, as adsorbed at three different water-polymer interfaces, were determined. The islet amyloid polypeptide most strongly adsorbed at a hydrophobic poly-(styrene) surface, whereas at a hydrophilic, negatively charged poly-(styrene sulfonate) interface, the degree of adsorption was reduced by 50%. Almost no IAPP adsorption was evident at this negatively charged interface when we added 100 mM NaCl. On the other hand, negatively charged insulin was most strongly attracted to a hydrophilic, negatively charged interface. Our results suggest that IAPP is strongly attracted to a hydrophobic surface, whereas the few positive charges of IAPP cannot warrant a permanent immobilization of IAPP at a hydrophilic, negatively charged surface at an ionic strength of 100 mM. Furthermore, the interfacial accumulation of insulin at a hydrophilic, negatively charged surface may represent a favorable precondition for nucleus formation and fibril formation.
Collapse
Affiliation(s)
- Christoph Jeworrek
- Fakultät Chemie, Technische Universität Dortmund, D-44221 Dortmund, Germany
| | | | | | | | | |
Collapse
|
20
|
Reichhart C, Czeslik C. Native-like structure of proteins at a planar poly(acrylic acid) brush. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:1047-1053. [PMID: 19099523 DOI: 10.1021/la802905s] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Applying ATR-FTIR (attenuated total reflection Fourier transform infrared) and TIRF (total internal reflection fluorescence) spectroscopy, we have studied the secondary structure and aggregation properties of different proteins which are adsorbed at a poly(acrylic acid) (PAA) brush that covers a macroscopically large, planar surface. The PAA brush has been prepared on the surface of an ATR silicon crystal or a quartz plate. The preparation includes the deposition of a thin poly(styrene) film by spin-coating and the transfer of the diblock copolymer poly(styrene)-poly(acrylic acid) onto the hydrophobic film using the Langmuir-Schafer technique. It has been found that the proteins hen egg white lysozyme, bovine serum albumin, bovine alpha-lactalbumin, and bovine insulin adsorb spontaneously at a PAA brush at neutral pD values, albeit to different degrees. The secondary structure of the proteins was estimated from a decomposition of the amide I'-band in the observed ATR-FTIR spectra. Generally, the fractions of secondary structure elements recovered in this way were almost identical to those found when the proteins are native in solution. In addition, the tendency of insulin to form amyloid fibrils has also been tested when the protein is adsorbed at a planar PAA brush. Insulin is known to form amyloid fibrils in solution at low pH values and elevated temperatures. The experiments performed in this study suggest that a PAA brush does not promote fibril formation of insulin. Rather, insulin that is adsorbed at a PAA brush seems to be excluded from fibril formation pathways even at pD = 2 and 60 degrees C, where fibril formation of insulin is triggered in solution. Overall, the results of this study demonstrate that a planar PAA brush may serve as a mild environment for immobilized proteins.
Collapse
|
21
|
Mitra L, Oleinikova A, Winter R. Intrinsic Volumetric Properties of Trialanine Isomers in Aqueous Solution. Chemphyschem 2008; 9:2779-84. [DOI: 10.1002/cphc.200800553] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
|
22
|
Liang Y, Pingali SV, Jogalekar AS, Snyder JP, Thiyagarajan P, Lynn DG. Cross-Strand Pairing and Amyloid Assembly. Biochemistry 2008; 47:10018-26. [DOI: 10.1021/bi801081c] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Yan Liang
- Center for Fundamental and Applied Molecular Evolution, Departments of Chemistry and Biology, Emory University, Atlanta, Georgia 30322, and Advance Photon Source, Argonne National Laboratory, Argonne, Illinois 60439
| | - Sai Venkatesh Pingali
- Center for Fundamental and Applied Molecular Evolution, Departments of Chemistry and Biology, Emory University, Atlanta, Georgia 30322, and Advance Photon Source, Argonne National Laboratory, Argonne, Illinois 60439
| | - Ashutosh S. Jogalekar
- Center for Fundamental and Applied Molecular Evolution, Departments of Chemistry and Biology, Emory University, Atlanta, Georgia 30322, and Advance Photon Source, Argonne National Laboratory, Argonne, Illinois 60439
| | - James P. Snyder
- Center for Fundamental and Applied Molecular Evolution, Departments of Chemistry and Biology, Emory University, Atlanta, Georgia 30322, and Advance Photon Source, Argonne National Laboratory, Argonne, Illinois 60439
| | - Pappannan Thiyagarajan
- Center for Fundamental and Applied Molecular Evolution, Departments of Chemistry and Biology, Emory University, Atlanta, Georgia 30322, and Advance Photon Source, Argonne National Laboratory, Argonne, Illinois 60439
| | - David G. Lynn
- Center for Fundamental and Applied Molecular Evolution, Departments of Chemistry and Biology, Emory University, Atlanta, Georgia 30322, and Advance Photon Source, Argonne National Laboratory, Argonne, Illinois 60439
| |
Collapse
|
23
|
Fulara A, Wojcik S, Loksztejn A, Dzwolak W. De novo Refolding and Aggregation of Insulin in a Nonaqueous Environment: An Inside out Protein Remake. J Phys Chem B 2008; 112:8744-7. [DOI: 10.1021/jp8029727] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Aleksandra Fulara
- Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland, and Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
| | - Sławomir Wojcik
- Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland, and Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
| | - Anna Loksztejn
- Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland, and Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
| | - Wojciech Dzwolak
- Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw, Poland, and Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
| |
Collapse
|
24
|
Partial molar volumes and adiabatic compressibilities of unfolded protein states. Biophys Chem 2008; 134:185-99. [PMID: 18342425 DOI: 10.1016/j.bpc.2008.02.009] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2008] [Revised: 02/12/2008] [Accepted: 02/12/2008] [Indexed: 11/22/2022]
Abstract
We determined the partial molar volumes, V degrees , and adiabatic compressibilities, K degrees (S), of N-acetyl amino acids with neutralized carboxyl termini, N-acetyl amino acid amides, and N-acetyl amino acid methylamides between 18 and 55 degrees C. The individual compounds in the three classes have been selected so as to collectively cover the 20 naturally occurring amino acid side chains. We interpret our experimental results in terms of the volumetric contributions and hydration properties of individual amino acid side chains and their constituent atomic groups. We also conducted pH-dependent densimetric and acoustic measurements to determine changes in volume and compressibility accompanying protonation of the aspartic acid, glutamic acid, histidine, lysine, and arginine side chains. We use our resulting data to develop an additive scheme for calculating the partial molar (specific) volume and adiabatic compressibility of fully extended polypeptide chains as a function of pH and temperature. We discuss the differences and similarities between our proposed scheme and the reported additive approaches. We compare our calculated volumetric characteristics of the fully extended conformations of apocytochrome c and apomyoglobin with the experimental values measured in water (for apocytochrome c) or acidic pH (for apomyoglobin). At these respective experimental conditions, the two proteins are unfolded. However, the comparison between the calculated and experimental volumetric characteristics suggests that neither apocytochrome c nor apomyoglobin are fully unfolded and retain a sizeable core of solvent-inaccessible groups.
Collapse
|
25
|
Effect of cholesterol and ergosterol on the compressibility and volume fluctuations of phospholipid-sterol bilayers in the critical point region: a molecular acoustic and calorimetric study. Biophys J 2008; 94:3538-48. [PMID: 18199673 DOI: 10.1529/biophysj.107.122549] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Although sterol-phospholipid interactions have been of interest for many years now, a complete thermodynamic profile of these systems is still missing. To contribute to a better understanding of the thermodynamic functions of these systems, we determined isothermal compressibility coefficient data for dipalmitoylphosphocholine (DPPC) and DPPC-containing cholesterol and ergosterol vesicles by means of molecular acoustics (ultrasound velocimetry and densimetry) and differential scanning and pressure perturbation calorimetric techniques. A particular focus was on the influence of the differential structural properties of the two sterols on the thermodynamic properties of lipid bilayers, and on the nature of the critical point region of phospholipid-sterol systems by determining thermodynamic fluctuation parameters. Contrary to significant changes in conformational and dynamical properties of the DPPC-sterol membranes, no marked differences were found in the various thermodynamic properties studied, including the adiabatic (beta(S)(lipid)) and isothermal (beta(T)(lipid)) compressibility, as well as the volume fluctuations. Differences in beta(T)(lipid) and beta(S)(lipid) become dramatic in the gel-fluid transition region only, due to a significant degree of slow relaxational processes in the microsecond time range in the transition region. Our data show no evidence for the existence of a typical critical point phenomenon in the concentration and temperature range where a critical point in the DPPC-sterol phase diagram is expected to appear. Hence, on a macroscopic level, it seems more appropriate to describe the sterol-phospholipid binary mixtures in the liquid-ordered/liquid-disordered coexistence region as a phase region consisting essentially of small nanodomains only. Such small-domain dimensions, with a series of particular properties such as increased line energy, spontaneous curvature, and limited lifetime, seem also to be typical of raftlike domains in cell membranes.
Collapse
|
26
|
Revealing different aggregation pathways of amyloidogenic proteins by ultrasound velocimetry. Biophys J 2008; 94:3241-6. [PMID: 18192359 DOI: 10.1529/biophysj.107.123133] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In this work, we performed a detailed thermodynamic study, including ultrasound velocimetry, densimetry, calorimetry, and FTIR spectroscopy, of an aggregation-prone protein (insulin) under different salt-screening conditions to gain a deeper insight into the scenario of physicochemical events during its temperature-induced unfolding and aggregation reactions. Differences in aggregation and fibrillization pathways are reflected in changes of the partial molar volume, the coefficients of thermal expansion and compressibility, and the infrared spectral properties of the protein. Combining all experimental data allows setting up a scheme for the temperature-dependent insulin aggregation reaction in the presence and absence of NaCl. As revealed by complementary atomic force microscopy studies, under charge-screening conditions, a process involving structural reorganization, ripening, and formation of more compact nuclei from amorphous oligomers is involved in the formation of mature fibrillar morphologies. In this work, our focus was to put forward a comprehensive discussion of the use of ultrasound velocimetry in disentangling different aggregation pathways. In fact, ultrasound velocimetry proved to be very sensitive to changes in aggregation pathway, highlighting the importance of density and compressibility changes in the different aggregation and fibrillization reactions of the protein.
Collapse
|
27
|
Javid N, Vogtt K, Krywka C, Tolan M, Winter R. Capturing the interaction potential of amyloidogenic proteins. PHYSICAL REVIEW LETTERS 2007; 99:028101. [PMID: 17678264 DOI: 10.1103/physrevlett.99.028101] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2007] [Indexed: 05/16/2023]
Abstract
Experimentally derived static structure factors obtained for the aggregation-prone protein insulin were analyzed with a statistical mechanical model based on the Derjaguin-Landau-Verwey-Overbeek potential. The data reveal that the protein self-assembles into equilibrium clusters already at low concentrations. Furthermore, striking differences regarding interaction forces between aggregation-prone proteins such as insulin in the preaggregated regime and natively stable globular proteins are found.
Collapse
Affiliation(s)
- Nadeem Javid
- University of Dortmund, Department of Chemistry, Physical Chemistry I-Biophysical Chemistry, Otto-Hahn Strasse 6, D-44227 Dortmund, Germany
| | | | | | | | | |
Collapse
|
28
|
Grudzielanek S, Velkova A, Shukla A, Smirnovas V, Tatarek-Nossol M, Rehage H, Kapurniotu A, Winter R. Cytotoxicity of Insulin within its Self-assembly and Amyloidogenic Pathways. J Mol Biol 2007; 370:372-84. [PMID: 17521669 DOI: 10.1016/j.jmb.2007.04.053] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2006] [Revised: 04/06/2007] [Accepted: 04/20/2007] [Indexed: 01/17/2023]
Abstract
Solvational perturbations were employed to selectively tune the aggregational preferences of insulin at 60 degrees C in vitro in purely aqueous acidic solution and in the presence of the model co-solvent ethanol (EtOH) (at 40%(w/w)). Dynamic light scattering (DLS), thioflavin T (ThT)-fluorescence, Fourier transform infrared (FTIR) and atomic force microscopy (AFM) techniques were employed to characterize these pathways biophysically with respect to the pre-aggregational assembly of the protein, the aggregation kinetics, and finally the aggregate secondary structure and morphology. Using cell viability assays, the results were subsequently correlated with the cytotoxicity of the insulin species that form in the two distinct aggregation pathways. In the cosolvent-free solution, predominantly dimeric insulin self-assembles via the well-known amyloidogenic pathway, yielding exclusively fibrillar aggregates, whereas in the solution containing EtOH, the aggregation of predominantly monomeric insulin proceeds via a pathway that leads to exclusively non-fibrillar, amorphous aggregates. Initially present native insulin assemblies as well as partially unfolded monomeric species and low molecular mass oligomeric aggregates could be ruled out as direct and major cytotoxic species. Apart from the slower overall aggregation kinetics under amorphous aggregate promoting conditions, which is due to the chaotropic nature of high EtOH concentrations, however, both pathways were unexpectedly found to evoke insulin aggregates that were cytotoxic to cultured rat insulinoma cells. The observed kinetics of the decrease of cell viabilities correlated well with the results of the DLS, ThT, FTIR and AFM studies, revealing that the formation of cytotoxic species correlated well with the formation of large-sized, beta-sheet-rich assemblies (>500 nm) of both fibrillar and amorphous nature. These results suggest that large-sized, beta-sheet-rich insulin assemblies of both fibrillar and amorphous nature are toxic to pancreatic beta-cells. In the light of the ongoing discussion about putative cytotoxic effects of prefibrillar and fibrillar amyloid aggregates, our results support the hypothesis that, in the case of insulin, factors other than the specific secondary or quarternary structural features of the various different aggregates may define their cytotoxic properties. Two such factors might be the aggregate size and the aggregate propensity to expose hydrophobic surfaces to a polar environment.
Collapse
Affiliation(s)
- Stefan Grudzielanek
- University of Dortmund, Department of Chemistry, Otto-Hahn-Str. 6, D-44227 Dortmund, Germany
| | | | | | | | | | | | | | | |
Collapse
|
29
|
Kraineva J, Smirnovas V, Winter R. Effects of lipid confinement on insulin stability and amyloid formation. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2007; 23:7118-26. [PMID: 17523690 DOI: 10.1021/la700405y] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
We report on a study of insulin incorporation into cubic phases of mono-olein (MO), using synchrotron small-angle X-ray scattering and FT-IR spectroscopy. We studied the thermal stability and aggregation scenario of insulin as a function of protein concentration in the narrow water channels of the cubic lipid matrix and compared it with data for insulin unfolding and fibrillation in bulk water solutions. The concomitant effect of insulin entrapment on the structure and phase behavior of the lipid matrix itself was also examined. We show that the protein's unfolding behavior and stability are influenced by confinement due to geometrical limitations, and vice versa, the topological properties of the lipid matrix change as well. The addition of insulin already at concentrations as low as 0.1 wt % significantly alters the phase behavior of MO. Surprisingly, new cubic structures are induced by insulin incorporation into the lipid matrix. When insulin begins to partially unfold at higher temperatures, the structure of the new cubic phase changes and finally disappears around 60 degrees C, where the aggregation process sets in. The aggregation in cubo proceeds much faster and leads to the formation of medium-sized oligomers or clusters, while the formation of large fibrillar agglomerates, as observed for bulk insulin aggregation, is largely prohibited. Hence, the results yield valuable information about the use of cubic mesoporous lipid systems as a medium for long-term storage of insulin and aggregation-prone proteins in general. Furthermore, the results provide new insights into the effects of soft-matter confinement on protein aggregation and fibrillation, a situation usually met in natural cell environments.
Collapse
Affiliation(s)
- Julia Kraineva
- Department of Chemistry, Physical Chemistry I-Biophysical Chemistry, University of Dortmund, Otto-Hahn Strasse 6, D-44227 Dortmund, Germany
| | | | | |
Collapse
|
30
|
Grudzielanek S, Smirnovas V, Winter R. The effects of various membrane physical-chemical properties on the aggregation kinetics of insulin. Chem Phys Lipids 2007; 149:28-39. [PMID: 17603032 DOI: 10.1016/j.chemphyslip.2007.05.006] [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: 02/28/2007] [Revised: 04/21/2007] [Accepted: 05/14/2007] [Indexed: 11/17/2022]
Abstract
In a simplified approach to the in vivo situation, where pathogenic fibrillar protein deposits are often found associated with cellular membranes, the aggregation kinetics of insulin in the presence of various model biomembranes were investigated using the Thioflavin T (ThT) fluorescence assay. The lipid dynamics near the gel-fluid transition, the chain length of saturated lipids and the presence of DOPE or DOPS in DOPC-vesicles modulate the aggregation kinetics of insulin in an indifferent, an aggregation-accelerating or an aggregation-inhibiting manner, subtly depending on the pH-value and the presence of salt. The rate of insulin aggregation in bulk solution dominates the overall aggregation process in most cases at low pH, where the lipid additives exert no effect on the aggregation kinetics. The occurrence of dynamic line defects near the gel-fluid transition temperature of DSPC facilitates a partial membrane insertion of the protein, which in turn shields exposed hydrophobic protein patches from intermolecular association and hence inhibit aggregation. An exclusively aggregation-accelerating effect was observed in the presence of 0.1M NaCl for all lipid additives investigated, which is likely due to an enhanced surface accumulation of the protein. Apart from weak dipole-dipole, dipole-monopole and hydrogen bonding interactions, the release of curvature elastic stress in mixed DOPC/DOPE-membranes and preferred interactions of insulin with carboxylic groups in DOPC/DOPS-membranes favour an increased surface accumulation. At neutral pH, a partial insertion of insulin into the lipid bilayer is favoured, which accounts for the aggregation-inhibiting effect of all lipid bilayer systems studied except those containing DOPS. Generally, the extent of inhibition increases with the lipid chain length and the extent of curvature stress in mixed unsaturated lipid membranes and also when the gel-fluid transition temperature of pure phospholipids is approached. The accelerating effect of DOPS on the aggregation of insulin under net electrostatic repulsion at pH 7.4 remains to be elucidated, yet, it might result from increased surface accumulation and/or faster/more extensive unfolding of the protein without a subsequent membrane insertion. These results demonstrate that a delicate interplay between different physical and chemical properties of lipid membranes has to be taken into account in a detailed discussion of membrane-associated protein aggregation phenomena.
Collapse
Affiliation(s)
- Stefan Grudzielanek
- University of Dortmund, Department of Chemistry, Physical Chemistry I-Biophysical Chemistry, Otto-Hahn Str. 6, D-44227 Dortmund, Germany
| | | | | |
Collapse
|