Hydrophobic protein stability

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... 

Kellis, J.T., et al. Contribution of hydrophobic interactions to protein stability. Nature 333 784-786, 1988. 

With a knowledge of the methodology in hand, let s review the results of amino acid composition and sequence studies on proteins. Table 5.8 lists the relative frequencies of the amino acids in various proteins. It is very unusual for a globular protein to have an amino acid composition that deviates substantially from these values. Apparently, these abundances reflect a distribution of amino acid polarities that is optimal for protein stability in an aqueous milieu. Membrane proteins have relatively more hydrophobic and fewer ionic amino acids, a condition consistent with their location. Fibrous proteins may show compositions that are atypical with respect to these norms, indicating an underlying relationship between the composition and the structure of these proteins. 

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. 

The following protocol for passive adsorption is based on methods reported for use with hydrophobic polymeric particles, such as polystyrene latex beads or copolymers of the same. Other polymer particle types also may be used in this process, provided they have the necessary hydrophobic character to promote adsorption. For particular proteins, conditions may need to be optimized to take into consideration maximal protein stability and activity after adsorption. Some proteins may undergo extensive denaturation after immobilization onto hydrophobic surfaces therefore, covalent methods of coupling onto more hydrophilic particle surfaces may be a better choice for maintaining native protein structure and long-term stability. 

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). 

No cysteine residues are found for alpha(sl) and P-caseins do. If any S-S bonds occur within the micelle, they are not the driving force for stabilization. Caseins are among the most hydrophobic proteins, and there is some evidence to suggest that they play a role in the stability of the micelle. It must be remembered that hydrophobic interactions are very temperature sensitive. 

Membranes are composed of lipids and proteins in varying combinations particular to each species, cell type, and organelle. The fluid mosaic model describes features common to all biological membranes. The lipid bilayer is the basic structural unit. Fatty acyl chains of phospholipids and the steroid nucleus of sterols are oriented toward the interior of the bilayer their hydrophobic interactions stabilize the bilayer but give it flexibility. 

T4 lysozyme 33,497 helix stability of 528, 529 hydrophobic core stability of 533, 544 Tanford j8 value 544, 555, 578, 582-Temperature jump 137, 138, 541 protein folding 593 Terminal transferase 408,410 Ternary complex 120 Tertiary structure 22 Theorell-Chance mechanism 120 Thermodynamic cycles 125-131 acid denaturation 516,517 alchemical steps 129 double mutant cycles 129-131, 594 mutant cycles 129 specificity 381, 383 Thermolysin 22, 30,483-486 Thiamine pyrophosphate 62, 83 - 84 Thionesters 478 Thiol proteases 473,482 TNfn3 domain O-value analysis 594 folding kinetics 552 Torsion angle 16-18 Tbs-L-phenylalanine chloromethyl ketone (TPCK) 278, 475 Transaldolase 79 Tyransducin-o 315-317 Transit time 123-125 Transition state 47-49 definition 55... 

The residues at positions a and d make up the hydrophobic core (Scheme 2). A portion of the buried surface area also comes from residues at positions e and g. Thus, interchain electrostatic attractions, for example, Lys at position g forming an i to i + 5 interaction with Glu at position e, cross the hydrophobic core, further burying these residues. The hydro-phobic interface includes residues a, d, e, and g (Scheme 2). An excellent colored spacefilling model of a two-stranded coiled coil showing these features is shown in a published review.114 These interchain and intrachain electrostatic attractions have been shown to contribute to protein stability (refs125,29,301 and references cited therein). 

Experimental studies of protein stabilities are numerous and there are still points of serious disagreement concerning the conclusions to be drawn from these studies. Areas of discord include the extent to which thermal denaturation corresponds to denaturation by chemical agents and the extent to which hydrophobic, van der Waals, and/or hydrogen bonds stabilize the native state. In this discussion, we will focus on the work of Peter L. Privalov.k Privalov has developed much of the microcalorimetric instrumentation that has made the calorimetric studies of proteins feasible. He has also published numerous review articles that summarize experimental data and formulate general observations concerning protein denaturation. His 1995 paper in Advances in Protein Chemistry9 presents a recent, comprehensive, review of the experimental results... 

Lu, S. M., and Hodges, R. S. (2004). Defining the minimum size of a hydrophobic cluster in two-stranded alpha-helical coiled-coils Effects on protein stability. Prot. Sci. 13, 714-726. 

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