Hydrophobic interactions in proteins

Size Isomers. In solution, hGH is a mixture of monomer, dimer, and higher molecular weight oligomers. Furthermore, there are aggregated forms of hGH found in both the pituitary and in the circulation (16,17). The dimeric forms of hGH have been the most carefully studied and there appear to be at least three distinct types of dimer a disulfide dimer connected through interchain disulfide bonds (8) a covalent or irreversible dimer that is detected on sodium dodecylsulfate- (SDS-)polyacrylamide gels (see Electroseparations, Electrophoresis) and is not a disulfide dimer (19,20) and a noncovalent dimer which is easily dissociated into monomeric hGH by treatment with agents that dismpt hydrophobic interactions in proteins (21). In addition, hGH forms a dimeric complex with ( 2). Scatchard analysis has revealed that two ions associate per hGH dimer in a cooperative... 

These bulky groups of distinctive shapes participate in hydrophobic interactions in protein interiors and in forming binding sites of specific shapes. 

In addition to the use of micelles as models for hydrophobic interactions in protein systems, information concerning the dilferent binding sites of protein molecules can be obtained by studying the elFects of surfactants on the properties of proteins and related compounds. The ensuing discussion is centered on these two applications of amphiphilic systems. 

Baldwin, R. L., Temperature dependence of the hydrophobic interaction in protein folding. Proc. Natl. Acad. Sci. USA 83, 8069-8072 (1986). 

A further indication of the potential for hydrophobic interactions in protein purification was given by Er-El, Zaidenzaig and Shaltiel [163]. A homologous series of hydrocarbon Sepharose derivatives were prepared with varying length alkyl side chains, viz. Sepharose-NH(CH2)nH. These... 

The molecular interpretation of thermodynamic data of temperature and pressure effects on proteins and their reactions is based on the data obtained from small molar mass model compounds in water. Weber and Drickamer [75] have pointed out the role of mechanical effects on the volume of association of molecular complexes by introducing molecular spacers that prevent molecules to get in close contact. As can be seen from Table 2, these mechanical effects can show up considerably in the volume changes, ft is clear that such effects should also influence hydrophobic interactions in proteins. 

For reasons discussed in detail by Singer (1971) the current concept of membrane structure is that of a lipid bilayer intercalated with proteins, referred to as the fluid mosaic model (Fig. 11). It is based primarily on thermodynamic arguments (Tanford, 1973) concerned with the fact that it is energetically favorable for the ionic portion of an amphipathic substance to be in direct contact with water while its hydrophobic tail is sequestered from water and interacts with other nonpolar molecules. The role of hydrophobic interactions in protein conformation was first emphasized by Kauzman (1959). It is not our purpose here to review the area of membrane structure (see articles by Singer, 1971 Tanford, 1973), but certain points are important to the discussion of effector functions. 

In chloroplasts of higher plants the ferredoxin-thioredoxin system links light-triggered events in thylakoid membranes with the regulation of enzymes in the stroma (1,2). If the conformation of enzymes changes because of modulators action then the surface exposed to the solvent will be different from the native state (3). As a consequence, interactions of modified enzymes with supramolecular structures (membranes, protein complexes) will differ respect to native forms. Since thylakoid membranes are complex structures they are not adequate for uncovering molecular mechanisms that participate in protein interactions(4). In thfe respect, the well-defined structure of micelles of non-ionic detergents constitute model compounds for the analysis of hydrophobic interactions in proteins (5,6). We report herein that chloroplast fructose-1,6-bisphosphatase interacts with micelles of Triton X-114 in a pH-dependent process. 

Proteins contain many nonpolar side chains. These side chains are repelled by water and tend to associate with one another on the inside of a folded protein molecule, out of contact with water. The tendency of nonpolar side chains to collect out of contact with the solvent is called the hydrophobic effect. The hydrophobic interactions in proteins are similar to those in the micelle of a soap (Section 21.5) or the bilayer of lipids in membranes. Hydrophobic interactions among nonpolar side chains in proteins are weak, but abundant, and are primarily responsible for maintaining the folded conformation of a protein. 

Tilton, R.D., Robertson, C.R., Gast, A.P., 1991. Manipulation of hydrophobic interactions in protein adsorption. Langmuir 7,2710. 

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