Hydrophobicity of protein

Differences in surface hydrophobicity of proteins Separates proteins on the basis of their isolectric points Complex interactions between proteins and the calcium phosphate-based media not fully understood... 

Protein separation by hydrophobic interaction chromatography is dependent upon interactions between the protein itself, the gel matrix and the surrounding aqueous solvent. Increasing the ionic strength of a solution by the addition of a neutral salt (e.g. ammonium sulfate or sodium chloride) increases the hydrophobicity of protein molecules. This may be explained (somewhat simplistically) on the basis that the hydration of salt ions in solution results in an ordered shell of water molecules forming around each ion. This attracts water molecules away from protein molecules, which in turn helps to unmask hydrophobic domains on the surface of the protein. 

Ca2+ influx initiates protein and membrane associations by several different mechanisms. Allosteric regulation of the hydrophobicity of protein-binding surfaces frequently occurs. One of the best studied examples is the Ca2+-dependent binding of calmodulin to other proteins (Ch. 22). Annexins are a family of proteins that exhibit Ca2+-dependent associations with cell membranes through direct interaction with phospholipids, and conversely, interactions with phospholipids increase their affinities for Ca2+ [7]. 

Protein prenylation leads to an increased hydrophobicity of proteins, typically resulting in an increased affinity for membranes. In 2004 studies on the cellular location of prenylated RhoB proteins showed that RhoB can undergo farnesylation (RhoB-F) as well as geranylgeranylation (RhoB-GG). With the aid of specific prenyl transferase inhibitors, it was revealed that RhoB-GG is localized to multivesicular late endosomes. 

Hydrophobic chromatography studies of proteins intramolecularly crosslinked to minimize unfolding suggest that .. . the effective hydrophobicity of proteins is due in part to the extent to which buried hydrophobic residues are exposed by protein unfolding (Ref.83), p. 97). 

Cardamone, M. and Puri, K. 1992. Spec-trofluorimetric assessment of the surface hydrophobicity of proteins. Biochem. J. 282 589-593. 

ANS (see Basic Protocol 1) has been the most popular hydrophobic probe for the determination of surface hydrophobicity of proteins. Its dimeric form bis-ANS, which has a greater quantum yield in nonpolar environments by binding more strongly with proteins than the ANS monomer, is occasionally used for the same purpose (Das and Surewicz, 1995). These effects permit the observation of depolarization by energy transfer among the bound fluoropho-res, which can be used to estimate the distribution of the ligands among the protein molecules (Farris et al., 1978). 

Cardamone and Puri (1992) stated that ANS binding and resultant Ka measured by a Scatchard plot or Kloz plot (and to a lesser extent quantum yield) may be used as a measure of the relative surface hydrophobicity of proteins. Titration of protein solutions with increasing concentrations of the fluorescent probe can provide information on both the number and the affinity of binding sites. This may be useful in determining whether the high value of fluorescence resulted from the presence of many binding sites of only moderate hydrophilic character, or from the existence of a high-affinity site with considerable hydrophilic character. 

Lieske, B. and Konrad, G. 1994. A new approach to estimate surface hydrophobicity of proteins. Milchwissenschaft 49 663-666. 

Tsutsui, T., Li-Chan, E and Nakai, S. 1986. A simple fluorometric method for fat-binding capacity as an index of hydrophobicity of proteins. J. Food Sci. 51 1268-1272. 

Ethanol appeared to modify flavor binding phenomena and it seemed that ethanol affected the conformational state of proteins. The relationship between the surface hydrophobicity of protein which informs on the conformational state and the... 

The study of the surface hydrophobicity of protein in the presence of ethanol confirmed the above result. The apparent dissociation constants for BSA and ovalbumin increased from 1.5 to 1.9x10 M and 6.8 to 7.9x10" M respectively in the presence of ethanol in citrate buffer (21), while the number of binding sites decreased from 22 to 10 for BSA and fi-om 40 to 19 for ovalbumin. Therefore it clearly appears that ethanol leads to modifications in protein conformation which causes changes in surface hydrophobicity. This result is consistent with the decrease in the binding of aroma compounds to proteins in the presence of ethanol... 

The hydrophobic effect refers to the favorable interactions between nonpolar surfaces immersed in water. These interactions are considered to provide the driving force for protein folding (44) and to make a major contribution to the stability of protein tertiary stractures. The hydrophobic effect also plays an important role in protein interactions (45). The hydrophobicity of protein surfaces has been studied experimentally by affinity partitioning of proteins (46). Theoretical studies have shown that the presence of hydrophobic patches on the surfaces of proteins correlates with protein binding sites (47 9). 

No direct investigation of the proposed first step—unfolding of the proteins at low temperatures—has appeared. Indirect evidence in favor of this occurrence is the reported decrease in hydrophobicity of proteins during hardening (see below). In opposition, however, is the fact that evaporative dehydration can apparently lead to the second step (aggregation) without the first. Conditions of this experiment seem to eliminate 0-5°... 

The common way to determine the hydrophobicity of a given molecule is based on its solubility in a polar or nonpolar medium. As most proteins are not soluble in nonpolar solvents, there was a need to use other methods to describe quantitatively the hydrophobicity of proteins. Because there is no standard method, we shall describe briefly some of the most common ones [4]. 

Gu X., Hewett-Emmett D., Li W.H. (1998). Directional mutational pressure alfects the amino acid composition and hydrophobicity of proteins in bacteria. Genetica 102/103 383-391. 

BER Berggren, K., Johansson, H.-O., and Tjemeld, F., Effects of salts and the surface hydrophobicity of proteins on partitioning in aqueous two-phase systems containing thermoseparating ethylene oxide-propylene oxide copolymers, J. Chromatogr. A, 718, 67, 1995. 

Bigelow, C. C. 1967. On the average hydrophobicity of proteins and the relation between it and protein structure. Journal ofTheoretical Biology 16 187-211. 

Giovambattista N, Lopez CF, Rossky PJ, Debenedetti PG (2008) Hydrophobicity of protein surfaces separating geometry from chemistry. Proc Natl Acad Sci 105(7) 2274—2279... 

Because of these restrictions, novel strategies for the predictable, controlled delivery of proteins are required. The high molecular weight and hydrophobicity of proteins cause the release rates obtained by predominantly diffusional processes to frequently be too slow in synthetic hydrophobic polymers to allow practical application. Significant current research activity therefore centers around the achievement of enhanced release by erosional breakdown of the polymer matrix. 

The importance of hydrophobic interactions in determining the spatial conformation of proteins and minimizing the free energy of their aqueous solutions has been stressed above. Formation and disruption of internal hydrophobic bonds is also essential for understanding denaturation phenomena of proteins and the mechanisms of their biological activity. The hydrophobicity of proteins and peptides affects their physicochemical behavior and may be of great value for their cosmetic effects and properties. 

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