Hydrophobicity scales

Last updated

Hydrophobicity scales are values that define the relative hydrophobicity or hydrophilicity of amino acid residues. The more positive the value, the more hydrophobic are the amino acids located in that region of the protein. These scales are commonly used to predict the transmembrane alpha-helices of membrane proteins. When consecutively measuring amino acids of a protein, changes in value indicate attraction of specific protein regions towards the hydrophobic region inside lipid bilayer.

Contents

The hydrophobic or hydrophilic character of a compound or amino acid is its hydropathic character, [1] hydropathicity, or hydropathy.

Hydrophobicity and the hydrophobic effect

Hydrogen bonds between molecules of liquid water Liquid water hydrogen bond.png
Hydrogen bonds between molecules of liquid water

The hydrophobic effect represents the tendency of water to exclude non-polar molecules. The effect originates from the disruption of highly dynamic hydrogen bonds between molecules of liquid water. Polar chemical groups, such as OH group in methanol do not cause the hydrophobic effect. However, a pure hydrocarbon molecule, for example hexane, cannot accept or donate hydrogen bonds to water. Introduction of hexane into water causes disruption of the hydrogen bonding network between water molecules. The hydrogen bonds are partially reconstructed by building a water "cage" around the hexane molecule, similar to that in clathrate hydrates formed at lower temperatures. The mobility of water molecules in the "cage" (or solvation shell) is strongly restricted. This leads to significant losses in translational and rotational entropy of water molecules and makes the process unfavorable in terms of free energy of the system. [2] [3] [4] [5] In terms of thermodynamics, the hydrophobic effect is the free energy change of water surrounding a solute. [6] A positive free energy change of the surrounding solvent indicates hydrophobicity, whereas a negative free energy change implies hydrophilicity. In this way, the hydrophobic effect not only can be localized but also decomposed into enthalpic and entropic contributions.

Types of amino acid hydrophobicity scales

A table comparing four different scales for the hydrophobicity of an amino acid residue in a protein with the most hydrophobic amino acids on the top Different hydrophobicity scales.png
A table comparing four different scales for the hydrophobicity of an amino acid residue in a protein with the most hydrophobic amino acids on the top

A number of different hydrophobicity scales have been developed. [3] [1] [7] [8] [9] The Expasy Protscale website lists a total of 22 hydrophobicity scales. [10]

There are clear differences between the four scales shown in the table. [11] Both the second and fourth scales place cysteine as the most hydrophobic residue, unlike the other two scales. This difference is due to the different methods used to measure hydrophobicity. The method used to obtain the Janin and Rose et al. scales was to examine proteins with known 3-D structures and define the hydrophobic character as the tendency for a residue to be found inside of a protein rather than on its surface. [12] [13] Since cysteine forms disulfide bonds that must occur inside a globular structure, cysteine is ranked as the most hydrophobic. The first and third scales are derived from the physiochemical properties of the amino acid side chains. These scales result mainly from inspection of the amino acid structures. [14] [1] Biswas et al., divided the scales based on the method used to obtain the scale into five different categories. [3]

Partitioning methods

The most common method of measuring amino acid hydrophobicity is partitioning between two immiscible liquid phases. Different organic solvents are most widely used to mimic the protein interior. However, organic solvents are slightly miscible with water and the characteristics of both phases change making it difficult to obtain pure hydrophobicity scale. [3] Nozaki and Tanford proposed the first major hydrophobicity scale for nine amino acids. [15] Ethanol and dioxane are used as the organic solvents and the free energy of transfer of each amino acid was calculated. Non liquid phases can also be used with partitioning methods such as micellar phases and vapor phases. Two scales have been developed using micellar phases. [16] [17] Fendler et al. measured the partitioning of 14 radiolabeled amino acids using sodium dodecyl sulfate (SDS) micelles. Also, amino acid side chain affinity for water was measured using vapor phases. [14] Vapor phases represent the simplest non polar phases, because it has no interaction with the solute. [18] The hydration potential and its correlation to the appearance of amino acids on the surface of proteins was studied by Wolfenden. Aqueous and polymer phases were used in the development of a novel partitioning scale. [19] Partitioning methods have many drawbacks. First, it is difficult to mimic the protein interior. [20] [21] In addition, the role of self solvation makes using free amino acids very difficult. Moreover, hydrogen bonds that are lost in the transfer to organic solvents are not reformed but often in the interior of protein. [22]

Accessible surface area methods

Hydrophobicity scales can also be obtained by calculating the solvent accessible surface areas for amino acid residues in the expended polypeptide chain [22] or in alpha-helix and multiplying the surface areas by the empirical solvation parameters for the corresponding types of atoms. [3] A differential solvent accessible surface area hydrophobicity scale based on proteins as compacted networks near a critical point, due to self-organization by evolution, was constructed based on asymptotic power-law (self-similar) behavior. [23] [24] This scale is based on a bioinformatic survey of 5526 high-resolution structures from the Protein Data Bank. This differential scale has two comparative advantages: (1) it is especially useful for treating changes in water-protein interactions that are too small to be accessible to conventional force-field calculations, and (2) for homologous structures, it can yield correlations with changes in properties from mutations in the amino acid sequences alone, without determining corresponding structural changes, either in vitro or in vivo.

Chromatographic methods

Reversed phase liquid chromatography (RPLC) is the most important chromatographic method for measuring solute hydrophobicity. [3] [25] The non polar stationary phase mimics biological membranes. Peptide usage has many advantages because partition is not extended by the terminal charges in RPLC. Also, secondary structures formation is avoided by using short sequence peptides. Derivatization of amino acids is necessary to ease its partition into a C18 bonded phase. Another scale had been developed in 1971 and used peptide retention on hydrophilic gel. [26] 1-butanol and pyridine were used as the mobile phase in this particular scale and glycine was used as the reference value. Pliska and his coworkers [27] used thin layer chromatography to relate mobility values of free amino acids to their hydrophobicities. About a decade ago, another hydrophilicity scale was published, this scale used normal phase liquid chromatography and showed the retention of 121 peptides on an amide-80 column. [28] The absolute values and relative rankings of hydrophobicity determined by chromatographic methods can be affected by a number of parameters. These parameters include the silica surface area and pore diameter, the choice and pH of aqueous buffer, temperature and the bonding density of stationary phase chains. [3]

Site-directed mutagenesis

This method use DNA recombinant technology and it gives an actual measurement of protein stability. In his detailed site-directed mutagenesis studies, Utani and his coworkers substituted 19 amino acids at Trp49 of the tryptophan synthase and he measured the free energy of unfolding. They found that the increased stability is directly proportional to increase in hydrophobicity up to a certain size limit. The main disadvantage of site-directed mutagenesis method is that not all the 20 naturally occurring amino acids can substitute a single residue in a protein. Moreover, these methods have cost problems and is useful only for measuring protein stability. [3] [29]

Physical property methods

Wimley-White whole-residue hydrophobicity scales Hydrophobicity scales2.gif
Wimley-White whole-residue hydrophobicity scales

The hydrophobicity scales developed by physical property methods are based on the measurement of different physical properties. Examples include, partial molar heat capacity, transition temperature and surface tension. Physical methods are easy to use and flexible in terms of solute. The most popular hydrophobicity scale was developed by measuring surface tension values for the naturally occurring 20 amino acids in NaCl solution. [30] The main drawbacks of surface tension measurements is that the broken hydrogen bonds and the neutralized charged groups remain at the solution air interface. [3] [1] Another physical property method involve measuring the solvation free energy. [31] The solvation free energy is estimated as a product of an accessibility of an atom to the solvent and an atomic solvation parameter. Results indicate the solvation free energy lowers by an average of 1 Kcal/residue upon folding. [3]

Whole-residue octanol-scale hydropathy plot for the L-subunit of the photosynthetic reaction center of Rhodobacter sphaeroides. Whole-Residue Hydropathy Plots.gif
Whole-residue octanol-scale hydropathy plot for the L-subunit of the photosynthetic reaction center of Rhodobacter sphaeroides.

Recent applications

Palliser and Parry have examined about 100 scales and found that they can use them for locating B-strands on the surface of proteins. [32] Hydrophobicity scales were also used to predict the preservation of the genetic code. [33] Trinquier observed a new order of the bases that better reflect the conserved character of the genetic code. [3] They believed new ordering of the bases was uracil-guanine-cystosine-adenine (UGCA) better reflected the conserved character of the genetic code compared to the commonly seen ordering UCAG. [3]

Wimley–White whole residue hydrophobicity scales

The Wimley–White whole residue hydrophobicity scales are significant for two reasons. First, they include the contributions of the peptide bonds as well as the sidechains, providing absolute values. Second, they are based on direct, experimentally determined values for transfer free energies of polypeptides.

Two whole-residue hydrophobicity scales have been measured:

The Stephen H. White website [34] provides an example of whole residue hydrophobicity scales showing the free energy of transfer ΔG(kcal/mol) from water to POPC interface and to n-octanol. [34] These two scales are then used together to make Whole residue hydropathy plots. [34] The hydropathy plot constructed using ΔGwoct − ΔGwif shows favorable peaks on the absolute scale that correspond to the known TM helices. Thus, the whole residue hydropathy plots illustrate why transmembrane segments prefer a transmembrane location rather than a surface one. [35] [36] [37] [38]

Amino acid Interface scale,
ΔGwif (kcal/mol)		Octanol scale,
ΔGwoct (kcal/mol)		Octanol − interface,
ΔGwoct − ΔGwif
Ile−0.31−1.12−0.81
Leu−0.56−1.25−0.69
Phe−1.13−1.71−0.58
Val0.07−0.46−0.53
Met−0.23−0.67−0.44
Pro0.450.14−0.31
Trp−1.85−2.09−0.24
His00.170.11−0.06
Thr0.140.250.11
Glu0−0.010.110.12
Gln0.580.770.19
Cys−0.24−0.020.22
Tyr−0.94−0.710.23
Ala0.170.500.33
Ser0.130.460.33
Asn0.420.850.43
Asp0−0.070.430.50
Arg+0.811.811.00
Gly0.011.151.14
His+0.962.331.37
Glu-2.023.631.61
Lys+0.992.801.81
Asp-1.233.642.41

Bandyopadhyay-Mehler protein structure based scales

Most of the existing hydrophobicity scales are derived from the properties of amino acids in their free forms or as a part of a short peptide. Bandyopadhyay-Mehler hydrophobicity scale was based on partitioning of amino acids in the context of protein structure. Protein structure is a complex mosaic of various dielectric medium generated by arrangement of different amino acids. Hence, different parts of the protein structure most likely would behave as solvents with different dielectric values. For simplicity, each protein structure was considered as an immiscible mixture of two solvents, protein interior and protein exterior. The local environment around individual amino acid (termed as "micro-environment") was computed for both protein interior and protein exterior. The ratio gives the relative hydrophobicity scale for individual amino acids. Computation was trained on high resolution protein crystal structures. This quantitative descriptor for microenvironment was derived from the octanol-water partition coefficient, (known as Rekker's Fragmental Constants) widely used for pharmacophores. This scale well correlate with the existing methods, based on partitioning and free energy computations. Advantage of this scale is it is more realistic, as it is in the context of real protein structures. [9]

Scale based on contact angle of water nanodroplet

Contact angles of a water nanodroplet on the artificial beta-sheets with various amino acid side chains Hydrophobicity scale based on contact angle.jpg
Contact angles of a water nanodroplet on the artificial beta-sheets with various amino acid side chains
The MD simulation system and the structure of artificial beta-folding 2D peptide network composed of unified R-side chains. Simulation system in hydrophobicity calculation.jpg
The MD simulation system and the structure of artificial beta-folding 2D peptide network composed of unified R-side chains.

In the field of engineering, the hydrophobicity (or dewetting ability) of a flat surface (e.g., a counter top in kitchen or a cooking pan) can be measured by the contact angle of water droplet. A University of Nebraska-Lincoln team recently devised a computational approach that can relate the molecular hydrophobicity scale of amino-acid chains to the contact angle of water nanodroplet. [39] The team constructed planar networks composed of unified amino-acid side chains with native structure of the beta-sheet protein. Using molecular dynamics simulation, the team is able to measure the contact angle of water nanodroplet on the planar networks (caHydrophobicity).

On the other hand, previous studies show that the minimum of excess chemical potential of a hard-sphere solute with respect to that in the bulk exhibits a linear dependence on cosine value of contact angle. [40] Based on the computed excess chemical potentials of the purely repulsive methane-sized Weeks–Chandler–Andersen solute with respect to that in the bulk, the extrapolated values of cosine value of contact angle are calculated(ccHydrophobicity), which can be used to quantify the hydrophobicity of amino acid side chains with complete wetting behaviors.

See also

Related Research Articles

In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent called the mobile phase, which carries it through a system on which a material called the stationary phase is fixed. Because the different constituents of the mixture tend to have different affinities for the stationary phase and are retained for different lengths of time depending on their interactions with its surface sites, the constituents travel at different apparent velocities in the mobile fluid, causing them to separate. The separation is based on the differential partitioning between the mobile and the stationary phases. Subtle differences in a compound's partition coefficient result in differential retention on the stationary phase and thus affect the separation.

<span class="mw-page-title-main">High-performance liquid chromatography</span> Technique in analytical chemistry

High-performance liquid chromatography (HPLC), formerly referred to as high-pressure liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify specific components in mixtures. The mixtures can originate from food, chemicals, pharmaceuticals, biological, environmental and agriculture, etc., which have been dissolved into liquid solutions.

In the physical sciences, a partition coefficient (P) or distribution coefficient (D) is the ratio of concentrations of a compound in a mixture of two immiscible solvents at equilibrium. This ratio is therefore a comparison of the solubilities of the solute in these two liquids. The partition coefficient generally refers to the concentration ratio of un-ionized species of compound, whereas the distribution coefficient refers to the concentration ratio of all species of the compound.

Salting out is a purification technique that utilizes the reduced solubility of certain molecules in a solution of very high ionic strength. Salting out is typically used to precipitate large biomolecules, such as proteins or DNA. Because the salt concentration needed for a given protein to precipitate out of the solution differs from protein to protein, a specific salt concentration can be used to precipitate a target protein. This process is also used to concentrate dilute solutions of proteins. Dialysis can be used to remove the salt if needed.

<span class="mw-page-title-main">Hydrophobic effect</span> Aggregation of non-polar molecules in aqueous solutions

The hydrophobic effect is the observed tendency of nonpolar substances to aggregate in an aqueous solution and to be excluded by water. The word hydrophobic literally means "water-fearing", and it describes the segregation of water and nonpolar substances, which maximizes the entropy of water and minimizes the area of contact between water and nonpolar molecules. In terms of thermodynamics, the hydrophobic effect is the free energy change of water surrounding a solute. A positive free energy change of the surrounding solvent indicates hydrophobicity, whereas a negative free energy change implies hydrophilicity.

Micellar electrokinetic chromatography (MEKC) is a chromatography technique used in analytical chemistry. It is a modification of capillary electrophoresis (CE), extending its functionality to neutral analytes, where the samples are separated by differential partitioning between micelles and a surrounding aqueous buffer solution.

<span class="mw-page-title-main">Paper chromatography</span> Separation of coloured chemicals on paper

Paper chromatography is an analytical method used to separate coloured chemicals or substances. It is now primarily used as a teaching tool, having been replaced in the laboratory by other chromatography methods such as thin-layer chromatography (TLC).

Lattice proteins are highly simplified models of protein-like heteropolymer chains on lattice conformational space which are used to investigate protein folding. Simplification in lattice proteins is twofold: each whole residue is modeled as a single "bead" or "point" of a finite set of types, and each residue is restricted to be placed on vertices of a lattice. To guarantee the connectivity of the protein chain, adjacent residues on the backbone must be placed on adjacent vertices of the lattice. Steric constraints are expressed by imposing that no more than one residue can be placed on the same lattice vertex.

<span class="mw-page-title-main">Ion chromatography</span> Separates ions and polar molecules

Ion chromatography is a form of chromatography that separates ions and ionizable polar molecules based on their affinity to the ion exchanger. It works on almost any kind of charged molecule—including small inorganic anions, large proteins, small nucleotides, and amino acids. However, ion chromatography must be done in conditions that are one pH unit away from the isoelectric point of a protein.

<span class="mw-page-title-main">Liquid–liquid extraction</span> Method to separate compounds or metal complexes

Liquid–liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds or metal complexes, based on their relative solubilities in two different immiscible liquids, usually water (polar) and an organic solvent (non-polar). There is a net transfer of one or more species from one liquid into another liquid phase, generally from aqueous to organic. The transfer is driven by chemical potential, i.e. once the transfer is complete, the overall system of chemical components that make up the solutes and the solvents are in a more stable configuration. The solvent that is enriched in solute(s) is called extract. The feed solution that is depleted in solute(s) is called the raffinate. Liquid–liquid extraction is a basic technique in chemical laboratories, where it is performed using a variety of apparatus, from separatory funnels to countercurrent distribution equipment called as mixer settlers. This type of process is commonly performed after a chemical reaction as part of the work-up, often including an acidic work-up.

<span class="mw-page-title-main">Solid-phase extraction</span> Process to separate compounds by properties

Solid-phase extraction (SPE) is a solid-liquid extractive technique, by which compounds that are dissolved or suspended in a liquid mixture are separated, isolated or purified, from other compounds in this mixture, according to their physical and chemical properties. Analytical laboratories use solid phase extraction to concentrate and purify samples for analysis. Solid phase extraction can be used to isolate analytes of interest from a wide variety of matrices, including urine, blood, water, beverages, soil, and animal tissue.

Chiral column chromatography is a variant of column chromatography that is employed for the separation of chiral compounds, i.e. enantiomers, in mixtures such as racemates or related compounds. The chiral stationary phase (CSP) is made of a support, usually silica based, on which a chiral reagent or a macromolecule with numerous chiral centers is bonded or immobilized.

<span class="mw-page-title-main">Hydrophilicity plot</span> Quantitative analysis of degree of hydrophobicity or hydrophilicity of amino acids of a protein

A hydrophilicity plot is a quantitative analysis of the degree of hydrophobicity or hydrophilicity of amino acids of a protein. It is used to characterize or identify possible structure or domains of a protein.

Reversed-phase liquid chromatography (RP-LC) is a mode of liquid chromatography in which non-polar stationary phase and polar mobile phases are used for the separation of organic compounds. The vast majority of separations and analyses using high-performance liquid chromatography (HPLC) in recent years are done using the reversed phase mode. In the reversed phase mode, the sample components are retained in the system the more hydrophobic they are.

<span class="mw-page-title-main">Hydrophilic interaction chromatography</span> Type of chromatography

Hydrophilic interaction chromatography is a variant of normal phase liquid chromatography that partly overlaps with other chromatographic applications such as ion chromatography and reversed phase liquid chromatography. HILIC uses hydrophilic stationary phases with reversed-phase type eluents. The name was suggested by Andrew Alpert in his 1990 paper on the subject. He described the chromatographic mechanism for it as liquid-liquid partition chromatography where analytes elute in order of increasing polarity, a conclusion supported by a review and re-evaluation of published data.

Implicit solvation is a method to represent solvent as a continuous medium instead of individual “explicit” solvent molecules, most often used in molecular dynamics simulations and in other applications of molecular mechanics. The method is often applied to estimate free energy of solute-solvent interactions in structural and chemical processes, such as folding or conformational transitions of proteins, DNA, RNA, and polysaccharides, association of biological macromolecules with ligands, or transport of drugs across biological membranes.

Protein precipitation is widely used in downstream processing of biological products in order to concentrate proteins and purify them from various contaminants. For example, in the biotechnology industry protein precipitation is used to eliminate contaminants commonly contained in blood. The underlying mechanism of precipitation is to alter the solvation potential of the solvent, more specifically, by lowering the solubility of the solute by addition of a reagent.

Micellar liquid chromatography (MLC) is a form of reversed phase liquid chromatography that uses an aqueous micellar solutions as the mobile phase.

Aqueous normal-phase chromatography (ANP) is a chromatographic technique that involves the mobile phase compositions and polarities between reversed-phase chromatography (RP) and normal-phase chromatography (NP), while the stationary phases are polar.

Chiral analysis refers to the quantification of component enantiomers of racemic drug substances or pharmaceutical compounds. Other synonyms commonly used include enantiomer analysis, enantiomeric analysis, and enantioselective analysis. Chiral analysis includes all analytical procedures focused on the characterization of the properties of chiral drugs. Chiral analysis is usually performed with chiral separation methods where the enantiomers are separated on an analytical scale and simultaneously assayed for each enantiomer.

References

  1. 1 2 3 4 Kyte, Jack; Doolittle, Russell F. (May 1982). "A simple method for displaying the hydropathic character of a protein". Journal of Molecular Biology. 157 (1). Elsevier BV: 105–32. CiteSeerX   10.1.1.458.454 . doi:10.1016/0022-2836(82)90515-0. PMID   7108955.
  2. ↑ Tanford, C., The hydrophobic effect(New York:Wiley.1980).
  3. 1 2 3 4 5 6 7 8 9 10 11 12 Biswas, Kallol M.; DeVido, Daniel R.; Dorsey, John G. (2003). "Evaluation of methods for measuring amino acid hydrophobicities and interactions". Journal of Chromatography A. 1000 (1–2). Elsevier BV: 637–655. doi:10.1016/s0021-9673(03)00182-1. ISSN   0021-9673. PMID   12877193.
  4. ↑ W . Kauzmann, Adv. Protein Chem. 14 (1959) 1.
  5. ↑ Charton, Marvin; Charton, Barbara I. (1982). "The structural dependence of amino acid hydrophobicity parameters". Journal of Theoretical Biology. 99 (4). Elsevier BV: 629–644. Bibcode:1982JThBi..99..629C. doi:10.1016/0022-5193(82)90191-6. ISSN   0022-5193. PMID   7183857.
  6. ↑ Schauperl, M; Podewitz, M; Waldner, BJ; Liedl, KR (2016). "Enthalpic and Entropic Contributions to Hydrophobicity". Journal of Chemical Theory and Computation. 12 (9): 4600–10. doi:10.1021/acs.jctc.6b00422. PMC   5024328 . PMID   27442443.
  7. ↑ Eisenberg D (July 1984). "Three-dimensional structure of membrane and surface proteins". Annu. Rev. Biochem. 53: 595–623. doi:10.1146/annurev.bi.53.070184.003115. PMID   6383201.
  8. ↑ Rose, G D; Wolfenden, R (1993). "Hydrogen Bonding, Hydrophobicity, Packing, and Protein Folding". Annual Review of Biophysics and Biomolecular Structure. 22 (1). Annual Reviews: 381–415. doi:10.1146/annurev.bb.22.060193.002121. ISSN   1056-8700. PMID   8347995.
  9. 1 2 Bandyopadhyay, D., Mehler, E.L. (2008). "Quantitative expression of protein heterogeneity: Response of amino acid side chains to their local environment". Proteins: Structure, Function, and Bioinformatics. 72 (2): 646–659. doi:10.1002/prot.21958. PMID   18247345. S2CID   20929779.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. ↑ "Expasy - ProtScale". web.expasy.org.
  11. ↑ "Hydrophobicity Scales".
  12. ↑ Janin, Joël (1979). "Surface and inside volumes in globular proteins". Nature. 277 (5696). Springer Science and Business Media LLC: 491–492. Bibcode:1979Natur.277..491J. doi:10.1038/277491a0. ISSN   0028-0836. PMID   763335. S2CID   4338901.
  13. ↑ Rose, G.; Geselowitz, A.; Lesser, G.; Lee, R.; Zehfus, M. (1985-08-30). "Hydrophobicity of amino acid residues in globular proteins". Science. 229 (4716). American Association for the Advancement of Science (AAAS): 834–838. Bibcode:1985Sci...229..834R. doi:10.1126/science.4023714. ISSN   0036-8075. PMID   4023714.
  14. 1 2 Wolfenden, R.; Andersson, L.; Cullis, P. M.; Southgate, C. C. B. (1981). "Affinities of amino acid side chains for solvent water". Biochemistry. 20 (4). American Chemical Society (ACS): 849–855. doi:10.1021/bi00507a030. ISSN   0006-2960. PMID   7213619.
  15. ↑ Y . Nozaki, C. Tanford, J. Biol. Chem. 246 (1971) 2211.
  16. ↑ Fendler, Janos H.; Nome, Faruk; Nagyvary, Joseph (1975). "Compartmentalization of amino acids in surfactant aggregates". Journal of Molecular Evolution. 6 (3). Springer Science and Business Media LLC: 215–232. Bibcode:1975JMolE...6..215F. doi:10.1007/bf01732358. ISSN   0022-2844. PMID   1206727. S2CID   2394979.
  17. ↑ Leodidis, Epaminondas B.; Hatton, T. Alan. (1990). "Amino acids in AOT reversed micelles. 2. The hydrophobic effect and hydrogen bonding as driving forces for interfacial solubilization". The Journal of Physical Chemistry. 94 (16). American Chemical Society (ACS): 6411–6420. doi:10.1021/j100379a047. ISSN   0022-3654.
  18. ↑ Sharp, Kim A.; Nicholls, Anthony; Friedman, Richard; Honig, Barry (1991-10-08). "Extracting hydrophobic free energies from experimental data: relationship to protein folding and theoretical models". Biochemistry. 30 (40). American Chemical Society (ACS): 9686–9697. doi:10.1021/bi00104a017. ISSN   0006-2960. PMID   1911756.
  19. ↑ Zaslavsky, B. Yu.; Mestechkina, N.M.; Miheeva, L.M.; Rogozhin, S.V. (1982). "Measurement of relative hydrophobicity of amino acid side-chains by partition in an aqueous two-phase polymeric system: Hydrophobicity scale for non-polar and ionogenic side-chains". Journal of Chromatography A. 240 (1). Elsevier BV: 21–28. doi:10.1016/s0021-9673(01)84003-6. ISSN   0021-9673.
  20. ↑ S . Damadoran, K.B. Song, J. Biol. Chem. 261 (1986) 7220.
  21. ↑ Ben-Naim, A. (1990-02-15). "Solvent effects on protein association and protein folding". Biopolymers. 29 (3). Wiley: 567–596. doi:10.1002/bip.360290312. ISSN   0006-3525. PMID   2331515. S2CID   25691137.
  22. 1 2 Chothia, Cyrus (1976). "The nature of the accessible and buried surfaces in proteins". Journal of Molecular Biology. 105 (1). Elsevier BV: 1–12. doi:10.1016/0022-2836(76)90191-1. ISSN   0022-2836. PMID   994183.
  23. ↑ Moret, M. A.; Zebende, G. F. (2007-01-19). "Amino acid hydrophobicity and accessible surface area". Physical Review E. 75 (1). American Physical Society (APS): 011920. Bibcode:2007PhRvE..75a1920M. doi:10.1103/physreve.75.011920. ISSN   1539-3755. PMID   17358197.
  24. ↑ Phillips, J. C. (2009-11-20). "Scaling and self-organized criticality in proteins: Lysozymec". Physical Review E. 80 (5). American Physical Society (APS): 051916. Bibcode:2009PhRvE..80e1916P. doi:10.1103/physreve.80.051916. ISSN   1539-3755. PMID   20365015.
  25. ↑ Hodges, Robert S.; Zhu, Bing-Yan; Zhou, Nian E.; Mant, Colin T. (1994). "Reversed-phase liquid chromatography as a useful probe of hydrophobic interactions involved in protein folding and protein stability". Journal of Chromatography A. 676 (1). Elsevier BV: 3–15. doi:10.1016/0021-9673(94)80452-4. ISSN   0021-9673. PMID   7921179.
  26. ↑ Aboderin, Akintola A. (1971). "An empirical hydrophobicity scale for α-amino-acids and some of its applications". International Journal of Biochemistry. 2 (11). Elsevier BV: 537–544. doi:10.1016/0020-711x(71)90023-1. ISSN   0020-711X.
  27. ↑ Pliška, Vladimir; Schmidt, Manfred; Fauchère, Jean-Luc (1981). "Partition coefficients of amino acids and hydrophobic parameters π of their side-chains as measured by thin-layer chromatography". Journal of Chromatography A. 216. Elsevier BV: 79–92. doi:10.1016/s0021-9673(00)82337-7. ISSN   0021-9673.
  28. ↑ Plass, Monika; Valko, Klara; Abraham, Michael H (1998). "Determination of solute descriptors of tripeptide derivatives based on high-throughput gradient high-performance liquid chromatography retention data". Journal of Chromatography A. 803 (1–2). Elsevier BV: 51–60. doi:10.1016/s0021-9673(97)01215-6. ISSN   0021-9673.
  29. ↑ Yutani, K.; Ogasahara, K.; Tsujita, T.; Sugino, Y. (1987-07-01). "Dependence of conformational stability on hydrophobicity of the amino acid residue in a series of variant proteins substituted at a unique position of tryptophan synthase alpha subunit". Proceedings of the National Academy of Sciences USA. 84 (13). Proceedings of the National Academy of Sciences: 4441–4444. Bibcode:1987PNAS...84.4441Y. doi: 10.1073/pnas.84.13.4441 . ISSN   0027-8424. PMC   305105 . PMID   3299367.
  30. ↑ Bull, Henry B.; Breese, Keith (1974). "Surface tension of amino acid solutions: A hydrophobicity scale of the amino acid residues". Archives of Biochemistry and Biophysics. 161 (2). Elsevier BV: 665–670. doi:10.1016/0003-9861(74)90352-x. ISSN   0003-9861. PMID   4839053.
  31. ↑ Eisenberg, David; McLachlan, Andrew D. (1986). "Solvation energy in protein folding and binding". Nature. 319 (6050). Springer Science and Business Media LLC: 199–203. Bibcode:1986Natur.319..199E. doi:10.1038/319199a0. ISSN   0028-0836. PMID   3945310. S2CID   21867582.
  32. ↑ Palliser, Christopher C.; Parry, David A. D. (2000). "Quantitative comparison of the ability of hydropathy scales to recognize surface ?-strands in proteins". Proteins: Structure, Function, and Genetics. 42 (2). Wiley: 243–255. doi:10.1002/1097-0134(20010201)42:2<243::aid-prot120>3.0.co;2-b. ISSN   0887-3585. PMID   11119649. S2CID   23839522.
  33. ↑ G . Trinquier, Y.-H. Sanejouand, Protein Eng. 11 (1998) 153.
  34. 1 2 3 White, Stephen (2006-06-29). "Experimentally Determined Hydrophobicity Scales". University of California, Irvine. Retrieved 2009-06-12.
  35. ↑ Wimley, William C.; White, Stephen H. (1996). "Experimentally determined hydrophobicity scale for proteins at membrane interfaces". Nature Structural & Molecular Biology. 3 (10). Springer Science and Business Media LLC: 842–848. doi:10.1038/nsb1096-842. ISSN   1545-9993. PMID   8836100. S2CID   1823375.
  36. ↑ Wimley, William C.; Creamer, Trevor P.; White, Stephen H. (1996). "Solvation Energies of Amino Acid Side Chains and Backbone in a Family of Host−Guest Pentapeptides". Biochemistry. 35 (16). American Chemical Society (ACS): 5109–5124. doi:10.1021/bi9600153. ISSN   0006-2960. PMID   8611495.
  37. ↑ White SH. & Wimley WC (1998). Biochim. Biophys. Acta 1376:339-352.
  38. ↑ White, Stephen H.; Wimley, William C. (1999). "MEMBRANE PROTEIN FOLDING AND STABILITY: Physical Principles". Annual Review of Biophysics and Biomolecular Structure. 28 (1). Annual Reviews: 319–365. doi:10.1146/annurev.biophys.28.1.319. ISSN   1056-8700. PMID   10410805.
  39. ↑ Zhu, Chongqin; Gao, Yurui; Li, Hui; Meng, Sheng; Li, Lei; Francisco, Joseph S; Zeng, Xiao Cheng (2016). "Characterizing hydrophobicity of amino acid side chains in a protein environment via measuring contact angle of a water nanodroplet on planar peptide network". Proceedings of the National Academy of Sciences. 113 (46): 12946–12951. Bibcode:2016PNAS..11312946Z. doi: 10.1073/pnas.1616138113 . PMC   5135335 . PMID   27803319.
  40. ↑ Godawat, R; Jamadagni, S. N; Garde, S (2009). "Characterizing hydrophobicity of interfaces by using cavity formation, solute binding, and water correlations". Proceedings of the National Academy of Sciences. 106 (36): 15119–15124. doi: 10.1073/pnas.0902778106 . PMC   2741215 . PMID   19706896.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.