Hydrophobic interactions globular proteins

It is clear that hydrophobic interactions are essential to the formation of the native structure of globular proteins. Again, thermodynamic studies [20] on such systems plus the analysis of protein crystal structures [30] are strong evidence for the essential role of these hydrophobic interactions. Globular proteins in their native conformation do have their hydrophobic atoms on the inside , away from the water, and the addition of non-aqueous solvents to the water tends to destabilize this structure, since the exposure of non-polar groups is not so energetically costly in e.g., mixed alcohol/water solvents as it is in pure water. 

The subunits of an oligomeric protein typically fold into apparently independent globular conformations and then interact with other subunits. The particular surfaces at which protein subunits interact are similar in nature to the interiors of the individual subunits. These interfaces are closely packed and involve both polar and hydrophobic interactions. Interacting surfaces must therefore possess complementary arrangements of polar and hydrophobic groups. 

The main contributions to AadsG for a globular protein are from electrostatic, dispersion, and hydrophobic forces and from changes in the structure of the protein molecule. Although in this section these contributions are discussed individually, strict separation of the influence of these forces on the overall adsorption process of a protein is not possible. For instance, adsorption-induced alteration of the protein structure affects the electrostatic and hydrophobic interaction between the protein and the surface. When the sorbent surface is not smooth but is covered with (polymeric)... 

Figure 11.5 Globular proteins. The folding of a polypeptide chain in a globular form is stabilized by hydrophobic interactions and some covalent bonding, particularly the disulphide bond between cysteine residues. The polypeptide chain shows some sections which are regular and helical in nature and other sections, particularly at bends and folds, where the conformation of the chain is distorted.

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). 

The structure and function of enzymes is determined by both the amino acid sequence and the surrounding solvent. The overall stability of proteins is characterized by a subtle balance of into- and inter-molecular interactions. The basic principle of the structure (and of the stability) of the proteins is related to the nature of its normal enviromnent for (water) soluble globular proteins this is the minimization of the hydrophobic surface area, whereas the contrary is the case for membrane proteins (Jaenicke, 1991). 

Protein structure is stabilized by multiple weak interactions. Hydrophobic interactions are the major contributors to stabilizing the globular form of most soluble proteins hydrogen bonds and ionic interactions are optimized in the specific structures that are thermodynamically most stable. 

Hydrophobic Effects. Hydrogen bonds and van der Waals forces are of major importance in determining the secondary structures formed by fibrous proteins. To understand the complex folded structures found in globular proteins additional types of interactions between amino acid side chains... 

The hydrophobic amino acid side chains on the exterior of the integral membrane protein interact with the hydrophobic lipid of the membrane exterior and are stable in the nonaqueous environment. These residues pack in the interior, hydrophobic environment of globular proteins. 

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