Proteins aggregation

The above analyses are based on equilibrium thermodynamics and require the experimental heat capacity data to accurately reflect the equilibrium protein unfolding [154]. It must be nevertheless recognized that, in many cases, the overall process that takes place during the DSC run is irreversible, as shown by the lack of thermal effect on reheating. 

Irreversible denaturation of simple proteins is often thought to involve at least two steps (i) reversible unfolding of the native protein (N), (ii) irreversible alteration of the unfolding protein (U) to yield a final state (F) that is unable to fold back to the native conformation [215,216] 

The two- step nature of the irreversible denaturation can be schematically described by the Lumry and Euring model [217] N --- U----- F. 

The importance of knowledge of these pH effects is particularly relevant in terms of food processing. For example a food area for which pH changes many impact food protein processing is the dairy industry. Although k-casein does not denature or show a DSC transition when heated up to 120 °C, other milk proteins 

Alkaline conditions destabilize the p-lactoglobulin protein. This was first observed using differential thermal analysis (DTA) where transition temperatures dropped from 81.5 to 66.5 °C as the pH was increased from 5.0 to 9.0 [227]. 

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A salient feature of natural surfaces is tliat tliey are overwhelmingly electron donors [133]. This is tlie basis for tlie ubiquitous hydrophilic repulsion which ensures tliat a cell can function, since massive protein-protein aggregation and protein-membrane adsorjition is tliereby prevented. In fact, for biomolecule interactions under typical physiological conditions, i.e. aqueous solutions of moderately high ionic strengtli, tlie donor-acceptor energy dominates. 

Before protein molecules attain their native folded state they may expose hydrophobic patches to the solvent. Isolated purified proteins will aggregate during folding even at relatively low protein concentrations. Inside cells, where there are high concentrations of many different proteins, aggregation could therefore occur during the folding process. This is prevented by... 

Petanate, A.M. and Glatz, C.E., 1983. Isoelectric precipitation of soy protein. I. Factors affecting particle size distributions. II. Kinetics of protein aggregate growth and breakage. Biotechnology and Bioengineering, 25, 3049. 

Column is clogged due to the presence of protein aggregates and/or insoluble residuals from biological samples... 

Molecular shape of the protein is not globular protein aggregates... 

ATP synthase actually consists of two principal complexes. The spheres observed in electron micrographs make up the Fj unit, which catalyzes ATP synthesis. These Fj spheres are attached to an integral membrane protein aggregate called the Fq unit. Fj consists of five polypeptide chains named a, j3, y, 8, and e, with a subunit stoichiometry ajjSaySe (Table 21.3). Fq consists of three hydrophobic subunits denoted by a, b, and c, with an apparent stoichiometry of ajbgCg.ig- Fq forms the transmembrane pore or channel through which protons move to drive ATP synthesis. The a, j3, y, 8, and e subunits of Fj contain 510, 482, 272, 146, and 50 amino acids, respectively, with a total molecular mass... 

Some ice creams contain sodium citrate to decrease the tendency of fat globules to coalesce, and to decrease protein aggregation. This results in a wetter ice cream. The citrates and phosphates are both used for this effect. Calcium and magnesium salts have the opposite effect, making a dryer ice cream. 

Coacervation occurs in tropoelastin solutions and is a precursor event in the assembly of elastin nanofibrils [42]. This phenomenon is thought to be mainly due to the interaction between hydro-phobic domains of tropoelastin. In scanning electron microscopy (SEM) picmres, nanofibril stmc-tures are visible in coacervate solutions of elastin-based peptides [37,43]. Indeed, Wright et al. [44] describe the self-association characteristics of multidomain proteins containing near-identical peptide repeat motifs. They suggest that this form of self-assembly occurs via specific intermolecular association, based on the repetition of identical or near-identical amino acid sequences. This specificity is consistent with the principle that ordered molecular assembhes are usually more stable than disordered ones, and with the idea that native-like interactions may be generally more favorable than nonnative ones in protein aggregates. 

The transmissible spongiform encephalopathies, or prion diseases, are fatal neurodegenerative diseases characterized by spongiform changes, astrocytic gliomas, and neuronal loss resulting from the deposition of insoluble protein aggregates in neural cells. They include Creutzfeldt-Jakob disease in humans, scrapie in... 

Hydrophobic interaction chromatograph (HIC), while very attractive in principle, has proved difficult to scale up for processing. A recent series of articles explores some of the unique problems associated with process-scale HIC. Load sample preparation20 must be carefully examined to prevent protein aggregate formation in the presence of the relatively high salt concentrations used in this technique. Successful scale-up also requires the setting of wide specifications to accomodate routine variations in the feed.21 The effect of the salt concentration on capacity may be somewhat more... 

Patapoff, T. W., Mrsny, R. J., and Lee, W. A., The application of size exclusion chromatography and computer simulation to study the thermodynamic and kinetic parameters for short-lived dissociable protein aggregates, Anal. Bio-chem., 212, 71, 1993. 

Loss of the native conformation of a protein generally exposes hydrophobic amino acid residues that are normally buried on the inside of the self-associated structure and are shielded from the aqueous environment. This leads to association between the exposed hydrophobic residues of neighboring proteins (aggregation) or between these exposed residues and hydrophobic surfaces that the protein may encounter either in the manufacturing process or in the primary package. 

Although ionic surfactants are often associated with denaturation of proteins [104], the nonionic surfactant polysorbate 80 has been included in several marketed formulations and serves to inhibit protein aggregation. The mechanism may be the greater tendency of the surfactant molecules to align themselves at the liquid/ air interface, excluding the protein from the interface and inhibiting surface denaturation. 

Ferrone F. Analysis of protein aggregation kinetics. Methods Enzymol 1999 309 256-274. 

Tomiyama T, Shoji A, Kataoka K, Suwa Y, Asano S, Kaneko H, Endo N. Inhibition of amyloid beta protein aggregation neurotoxicity by rifampicin. Its possible function as a hydroxyl radical scavenger. J Biol Chem 1996 271 6839-6844. 

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