Proteins hydrophobic effect

Water-soluble globular proteins usually have an interior composed almost entirely of non polar, hydrophobic amino acids such as phenylalanine, tryptophan, valine and leucine witl polar and charged amino acids such as lysine and arginine located on the surface of thi molecule. This packing of hydrophobic residues is a consequence of the hydrophobic effeci which is the most important factor that contributes to protein stability. The molecula basis for the hydrophobic effect continues to be the subject of some debate but is general considered to be entropic in origin. Moreover, it is the entropy change of the solvent that i... 

Fig. 5. Protein folding. The unfolded polypeptide chain coUapses and assembles to form simple stmctural motifs such as -sheets and a-hehces by nucleation-condensation mechanisms involving the formation of hydrogen bonds and van der Waal s interactions. Small proteins (eg, chymotrypsin inhibitor 2) attain their final (tertiary) stmcture in this way. Larger proteins and multiple protein assembhes aggregate by recognition and docking of multiple domains (eg, -barrels, a-helix bundles), often displaying positive cooperativity. Many noncovalent interactions, including hydrogen bonding, van der Waal s and electrostatic interactions, and the hydrophobic effect are exploited to create the final, compact protein assembly. Further stmctural...

Prevost, M. Wodak, S. J. Tidor, B. Karplus, M., Contribution of the hydrophobic effect to protein stability — analysis based on simulations of the Ile-96- Ala mutation in barnase, Proc. Natl Acad. Sci. USA 1991, 88,10880-10884. 

Protein molecules contain both polar and apolar groups. For proteins dissolved in water, these apolar groups tend to be buried in the interior of the globular structure, as a result of expulsion by the surrounding water. However, other interactions, as well as geometrical constraints, interfere with the hydrophobic effect, so that a minor fraction of the water-accessible surface of the protein molecule may be apolar. Protein molecules that do not spontaneously aggregate in water do not have pronounced apolar patches at their surfaces. 

Szleifer I (1997) Protein adsorption on surfaces with grafted polymers a theoretical approach. Biophys J 72 595-612 Tanford C (1973) The hydrophobic effect. John Wiley Sons, Inc., Hoboken Van Dulm P, Norde W, Lyklema J (1981) Ion participation in protein adsorption at solid surfaces. J Colloid Interf Sci 82 77-82 Zoungrana T, Findenegg GH, Norde W (1997) Structure, stability and activity of adsorbed ensymes. J Colloid Interf Sci 190 437-448 Zoungrana T, Norde W (1997) Thermal stability and enzymatic activity of a-chymotrypsin adsorbed on polystyrene surfaces. Colloid Surf B 9 157-167... 

When the hydrophobic effect brings atoms very close together, van der Waals interactions and London dispersion forces, which work only over very short distances, come into play. This brings things even closer together and squeezes out the holes. The bottom line is a very compact, hydrophobic core in a protein with few holes. 

Hydrophobic interactions are the single most important stabilizing influence of protein native structure. The hydrophobic effect refers to the tendency of non-polar substances to minimize contact with a polar solvent such as water. Non-polar amino acid residues constitute a significant proportion of the primary sequence of virtually all polypeptides. These polypeptides will fold in such a way as to maximize the number of such non-polar residue side chains buried in the polypeptide s interior, i.e. away from the surrounding aqueous environment. This situation is most energetically favourable. 

Biological membranes consist of a bilayer of phospholipids in which membrane proteins are either embedded (integral proteins) or simply adsorbed (boundary proteins) (1) (Figure 1.). These systems fulfill a variety of functions oT basic importance. One of the most significant is the compartimentation via the formation of cells and cell subunits based on the self organization of membranes (hydrophobic effect (2j). 

Physical properties of the protein structure should be considered in designing strategies to achieve stable formulations because they can often yield clues about which solution environment would be appropriate for stabilization. For example, the insulin molecule is known to self-associate via a nonspecific hydrophobic mechanism66 Stabilizers tested include phenol derivatives, nonionic and ionic surfactants, polypropylene glycol, glycerol, and carbohydrates. The choice of using stabilizers that are amphiphilic in nature to minimize interactions where protein hydrophobic surfaces instigate the instability is founded upon the hydro-phobic effect.19 It has already been mentioned that hydrophobic surfaces prefer... 

The native conformation of proteins is stabilized by a number of different interactions. Among these, only the disulfide bonds (B) represent covalent bonds. Hydrogen bonds, which can form inside secondary structures, as well as between more distant residues, are involved in all proteins (see p. 6). Many proteins are also stabilized by complex formation with metal ions (see pp. 76, 342, and 378, for example). The hydrophobic effect is particularly important for protein stability. In globular proteins, most hydrophobic amino acid residues are arranged in the interior of the structure in the native conformation, while the polar amino acids are mainly found on the surface (see pp. 28, 76). 

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