Protein stability intrinsic

The protein s intrinsic properties (size, molecular weight, 3-D structure, surface site density, conformational stability) are all very important and must be fully characterized and understood in order to interpret adsorption data. 

The term thermal stability (also thermostability) refers to the resistance of a protein to adverse intrinsic and extrinsic environmental influences, i.e., the thermal characteristic of the protein to remain steady against the dena-turation of its molecular integrity and inactivation of its biologic activity on facing high temperatures or other deleterious agents (6). One of the most important indices to measure protein stability is the decimal reduction time, or D-value, the time required to reduce 90% of the initial protein concentration exposed to the reference temperature. The D-value was used... 

Sarmento, M.R., Oliveira, J.C., Slatner, M. and Boulton, R.B. (2000) Influence of intrinsic factors on conventional wine protein stability tests, Food Control, 11, 423-432. 

Many proteins, particularly those of eukaryotic origin, require an interacting protein partner for correct folding and stability.190-193 Often, these proteins contain intrinsically disordered domains that mediate the protein interaction. Frequently, proteins with unstructured domains cannot be expressed solubly in E. coli. In some cases, coexpression of the interacting protein has improved the stability and solubility of the protein of interest.194-197 As an example, the yield of inducible nitric oxide synthase (iNOS) was 20—25 times greater when coexpressed with its natural partner, calmodulin, than in the absence of calmodulin. Additionally, soluble iNOS could be isolated when expressed without calmodulin but it was deficient in heme and flavins and almost completely inactive.198 Methods for coexpression in both prokaryotic and eukaryotic hosts have been recently reviewed.1... 

Because protein-ba sed foams depend upon the intrinsic molecular properties (extent and nature of protein-protein interactions) of the protein, foaming properties (formation and stabilization) can vary immensely between different proteins. The intrinsic properties of the protein together with extrinsic factors (temperature, pH, salts, and viscosity of the continuous phase) determine the physical stability of the film. Films with enhanced mechanical strength (greater protein-protein interactions), and better rheological and viscoelastic properties (flexible residual tertiary structure) are more stable (12,15), and this is reflected in more stable foams/emulsions (14,33). Such films have better viscoelastic properties (dilatational modulus) ( ) and can adapt to physical perturbations without rupture. This is illustrated by -lactoglobulin which forms strong viscous films while casein films show limited viscosity due to diminished protein-protein (electrostatic) interactions and lack of bulky structure (steric effects) which apparently improves interactions at the interface (7,13 19). 

TABLE IV Strategies for Intrinsic Protein Stabilization Gained from Crystal Structure of TmLDH" ... 

The key question we want to answer is what are the intrinsic sequence dependent factors tliat not only detennine tire folding rates but also tire stability of tire native state It turns out tliat many of tire global aspects of tire folding kinetics of proteins can be understood in tenns of tire equilibrium transition temperatures. In particular, we will show tliat tire key factor tliat governs tire foldability of sequences is tire single parameter... 

In Figure 7b, the data are plotted as AG yielding a linear function. Extrapolation to 2ero denaturant provides a quantitative estimate of the intrinsic stability of the protein, AG, which in principle is the free energy of unfolding for the protein in the absence of denaturant. Comparison of the AG values between mutant and wild-type proteins provides a quantitative means of assessing the effects of point mutations on the stability of a protein. 

In the native protein these less stable ds-proline peptides are stabilized by the tertiary structure but in the unfolded state these constraints are relaxed and there is an equilibrium between ds- and trans-isomers at each peptide bond. When the protein is refolded a substantial fraction of the molecules have one or more proline-peptide bonds in the incorrect form and the greater the number of proline residues the greater the fraction of such molecules. Cis-trans isomerization of proline peptides is intrinsically a slow process and in vitro it is frequently the rate-limiting step in folding for those molecules that have been trapped in a folding intermediate with the wrong isomer. 

The enrichments and depletions displayed in Figure 1 are concordant with what would be expected if disorder were encoded by the sequence (Williams et al., 2001). Disordered regions are depleted in the hydrophobic amino acids, which tend to be buried, and enriched in the hydrophilic amino acids, which tend to be exposed. Such sequences would be expected to lack the ability to form the hydrophobic cores that stabilize ordered protein structure. Thus, these data strongly support the conjecture that intrinsic disorder is encoded by local amino acid sequence information, and not by a more complex code involving, for example, lack of suitable tertiary interactions. 

L. Zheng and J.D. Brennan, Measurement of intrinsic fluorescence to probe the conformational flexibility and thermodynamic stability of a single tryptophan protein entrapped in a sol-gel derived glass matrix. Analyst 123, 1735-1744 (1998). 

Antiapoptotic proteins. There are many different intracellular proteins that can prevent apoptosis by inhibiting specific steps in the cell death process. These include Bcl-2 family members such as Bcl-2 and Bcl-xL which can stabilize (mitochondrial, ER and plasma) membranes (Bcl-2 may also have intrinsic antioxidant activity). Other proteins, IAPs such as XIAP (X-linked) and NIAP (neuronal), which can directly inhibit caspases [31]. Additional examples of antiapoptotic proteins include protease inhibitors such as calpastatin, and protein chaperones such as GRP-78 and heat shock protein (HSP)-70. 

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